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With the advent of personalized medical approaches, precise and tailored treatments are expected to become widely accepted for the prevention and treatment of diabetes. Paper-based colorimetric sensors that function in combination with smartphones have been rapidly developed in recent years because it does not require additional equipment and is inexpensive and easy to perform. In this study, we developed a portable, low-cost, and wearable sweat-glucose detection device for in situ detection. The sensor adopted an integrated biomimetic nanoenzyme of glucose oxidase (GOx) encapsulated in copper 1, 4-benzenedicarboxylate (CuBDC) (GOx@CuBDC) through a biomimetic mineralization process. CuBDC exhibited a peroxide-like effect, cascade catalytic effect with the encapsulated GOx, and increased the enzyme stability. GOx@CuBDC and 3,3,5,5-tetramethylbenzidine were combined to form a hybrid membrane that achieved single-step paper-based glucose detection. This GOx@CuBDC-based colorimetric glucose sensor was used to quantitatively analyze the sweat-glucose concentration with smartphone readings. The sensor exhibited a good linear relationship over the concentration range of 40–900 μM and a limit of detection of 20.7 μM (S/N = 3). Moreover, the sensor performed well in situ monitoring and in evaluating variations based on the consumption of foods with different glycemic indices. Therefore, the fabricated wearable sweat-glucose sensors exhibited optimal practical application performance. GOx@CuBDC synthesis, sensor fabrication, sweat glucose induced colorimetric signal generation and smartphone readout. [Display omitted] • A wearable sweat glucose colorimetric sensors based on self-assembly of cascade nanozyme. • The biomimetic nanozyme can catalyzes the glucose cascade reaction then produced color changes. • A simple production, cost-effective sensing platform with good sensitivity and strong stability. • The variation tendency of sweat glucose concentration was detected in subjects after different meals ingested. [ABSTRACT FROM AUTHOR]

The monitoring of biomarkers in wound exudate is of great importance for wound care and treatment, and electrochemical biosensors with high sensitivity are potentially useful for this purpose. However, conventional electrochemical biosensors always suffer from severe biofouling when performed in the complex wound exudate. Herein, an antifouling electrochemical biosensor for the detection of involucrin in wound exudate was developed based on a wound dressing, oxidized bacterial cellulose (OxBC) and quaternized chitosan (QCS) composite hydrogel. The OxBC/QCS hydrogel was prepared using an in-situ chemical oxidation and physical blending method, and the proportion of OxBC and QCS was optimized to achieve electrical neutrality and enhanced hydrophilicity, therefore endowing the hydrogel with exceptional antifouling and antimicrobial properties. The involucrin antibody SY5 was covalently bound to the OxBC/QCS hydrogel to construct the biosensor, and it demonstrated a low limit of detection down to 0.45 pg mL−1 and a linear detection range from 1.0 pg mL−1 to 1.0 μg mL−1, and it was capable of detecting targets in wound exudate. Crucially, the unique antifouling and antimicrobial capability of the OxBC/QCS hydrogel not only extends its effective lifespan but also guarantees the sensing performance of the biosensor. The successful application of this wound dressing, OxBC/QCS hydrogel for involucrin detection in wound exudate demonstrates its promising potential in wound healing monitoring. An antifouling and antibacterial electrochemical biosensor was constructed for the detection of Involucrin (IVL) in wound exdaute. [Display omitted] • An electrochemical biosensor with both antifouling and antimicrobial capabilities was developed. • Oxidized bacterial cellulose and quaternized chitosan were used to prepare composite hydrogel. • The antifouling biosensor was able to detect involucrin in wound exudate with acceptable accuracy. [ABSTRACT FROM AUTHOR]

Non-invasive indirect blood glucose monitoring can be realized by detecting low concentrations of glucose (0.05–5 mM) in tears, but sensitive optical indicators are required. The intensity of the phosphorescence of a candidate optical indicator, palladium hematoporphyrin monomethyl ether (Pd-HMME), is increased by oxygen consumption under sealed conditions in the presence of glucose and glucose oxidase. However, the glucose detection limit based on this mechanism is high (800 μM) because the phosphorescence is completely quenched under ambient oxygen conditions and hence a large amount of glucose is required to reduce the oxygen levels such that the phosphorescence signal is detectable. To improve the glucose detection limit of Pd-HMME phosphorescence-based methods, the triplet protector imidazole was introduced, and strong phosphorescence was observed under ambient oxygen conditions. Detectable phosphorescence enhancement occurred at low glucose concentrations (<200 μM). Linear correlation between the phosphorescence intensity and glucose concentration was observed in the range of 30–727 μM (R 2 = 99.9 %), and the detection limit was ∼10 μM. The glucose sensor has a fast response time (∼90 s) and excellent selectivity for glucose. These results indicate the potential of the developed optical indicator for fast, selective, and reliable low-concentration glucose sensing. The triplet protector imidazole was introduced to a metalloporphyrin solution and strong phosphorescence was observed under ambient oxygen conditions. Obvious phosphorescence enhancement occurred in the presence of low concentrations of glucose, and a much-reduced detection limit was obtained. [Display omitted] • Imidazole is an effective triplet protector for Pd-porphyrin. • The glucose detection limit of Pd-porphyrin is improved by imdazole • A lower glucose detection limit of ∼10 μM was achieved. • Phosphorescence intensity and glucose concentration were linearly correlated. [ABSTRACT FROM AUTHOR]

Diabetes is a significant health threat, with its prevalence and burden increasing worldwide indicating its challenge for global healthcare management. To decrease the disease severity, the diabetic patients are recommended to regularly check their blood glucose levels. The conventional finger-pricking test possesses some drawbacks, including painfulness and infection risk. Nowadays, smartphone has become a part of our lives offering an important benefit in self-health monitoring. Thus, non-invasive wearable sweat glucose sensor connected with a smartphone readout is of interest for real-time glucose detection. Wearable sweat glucose sensing device is fabricated for self-monitoring of diabetes. This device is designed as a body strap consisting of a sensing strip and a portable potentiostat connected with a smartphone readout via Bluetooth. The sensing strip is modified by carbon nanotubes (CNTs)-cellulose nanofibers (CNFs), followed by electrodeposition of Prussian blue. To preserve the activity of glucose oxidase (GOx) immobilized on the modified sensing strip, chitosan is coated on the top layer of the electrode strip. Herein, machine learning is implemented to correlate between the electrochemical results and the nanomaterial content along with deposition cycle of prussian blue, which provide the highest current response signal. The optimized regression models provide an insight, establishing a robust framework for design of high-performance glucose sensor. This wearable glucose sensing device connected with a smartphone readout offers a user-friendly platform for real-time sweat glucose monitoring. This device provides a linear range of 0.1–1.5 mM with a detection limit of 0.1 mM that is sufficient enough for distinguishing between normal and diabetes patient with a cut-off level of 0.3 mM. This platform might be an alternative tool for improving health management for diabetes patients. [Display omitted] • A body strap sweat glucose sensor connected to a smartphone for real-time glucose detection is fabricated. • The sensing strip of wearable glucose sensor is modified by PB/CNTs-CNFs nanocomposite. • The key experimental parameters affecting the response signal are optimized and confirmed by ML. • This device is able to detect sweat glucose at a cut-off value for indicating diabetes prone patients. [ABSTRACT FROM AUTHOR]

Salmonella Typhimurium poses a serious threat to human health worldwide, necessitating the development of a rapid, sensitive, and convenient method for S. Typhimurium detection. Nanozymes are considered ideal signal report elements, which are extensively used for developing colorimetric methods. However, single-component nanozymes display low catalytic activity, and colorimetric methods are susceptible to environmental interference, reducing the sensitivity and accuracy of detection results. To address these drawbacks, this study constructed a dual-mode composite nanozyme-based cascade colorimetric-fluorescence aptasensor for S. Typhimurium detection in food. In this study, the composite Fe 3 O 4 @MIL-100(Fe) nanozymes were successful synthesized and demonstrated substantial peroxide-like activity, with 4.76-fold higher specificity activity (SA) than that of Fe 3 O 4 nanozymes. Then, a glucose oxidase (GOx)-Fe 3 O 4 @MIL-100(Fe) cascade reaction was developed for colorimetric detection via an aptamer to facilitate the formation of Fe 3 O 4 @MIL-100(Fe)/ S. Typhimurium/carboxylated g-C 3 N 4 (CCN)-GOx sandwich complexes. Meanwhile, the fluorescence mode was achieved by measuring the fluorescence intensity of the sandwich complexes. In optimum conditions, the dual-mode detection limits (LOD) were 1.8 CFU/mL (colorimetric mode) and 1.2 CFU/mL (fluorescence mode), respectively, with the S. Typhimurium concentration ranging from 10 CFU/mL to 107 CFU/mL. Finally, the feasibility of the dual-mode colorimetric-fluorescence method was validated via three actual samples, yielding recovery rates of 77.32 % to91.17 % and 82.17 % to 103.7 %, respectively. This study successfully develops a composite nanozyme-based cascade colorimetric and fluorescence dual-mode aptasensor for S. Typhimurium detection. It presents several distinct benefits, such as a broader linear range (10–107 CFU/mL), a lower LOD value (1.2 CFU/mL), and more accurate results. More importantly, the proposed dual-mode method displays a low LOD in colorimetric mode, demonstrating considerable potential for S. Typhimurium on-site detection in food. [Display omitted] • A nanozyme cascade reaction was developed to improve the sensitivity of results. • The fluorescence method was introduced to improve the accuracy of results. • This dual-mode detection limits for bacteria were 1.8 and 1.2 CFU/mL, respectively. [ABSTRACT FROM AUTHOR]

Recently, various techniques have been developed to accurately and sensitively detect tumor biomarkers for the early diagnosis and effective therapy of cancer. The electrochemiluminescence (ECL) method holding outstanding features including high sensitivity, ease of operation, and spatiotemporal controllability exhibited great potential for DNA/RNA detection, immunoassay, cancer cell detection, and environmental analysis. However, a glaring problem of ECL approaches is that the layer-by-layer modification on the electrode leads to poor stability and sensitivity of the sensors. Therefore, new simple and efficient methods for electrode modification which can effectively improve the ECL signal have attracted more and more research interests. Based on the dual amplification strategy of target-induced CHA and nanocomposite probes leading to self-generated co-reactant (H 2 O 2), we proposed a highly sensitive miRNA-ECL detection system. The introduction of the target miRNA-21 triggers the CHA cycle amplification of DNA1 and biotin-modified DNA2, releasing the target miRNA-21 sequence for the target cycle reaction. After the reaction, the newly introduced DNA2 was combined with Au NPs modified with SA and Glucose oxidase (GOD). In the presence of oxygen, glucose was decomposed by GOD to produce H 2 O 2 , and then H 2 O 2 was immediately catalyzed by the Hemin/G-quadruplex at the double-stranded end of the CHA product to produce a large amount of O 2 −•. As a co-reactant of luminol, the ECL signal was significantly enhanced, thereby achieving highly sensitive detection of miRNA-21 content and obtaining a low detection limit of 0.65 fM. The high specificity of the ECL biosensor was also proved by base mismatch. Compared with other current detection methods, this sensor can achieve quantitative analysis of other target analytes by flexibly changing the probe DNA sequence, and provide a new feasible solution for the detection of tumor-associated markers. Benefiting from the improved sensitivity and selectivity, the proposed biosensing platform is expected to provide a new strategy for biomarkers analysis and outstanding prospect for further clinical application. We designed a highly sensitive miRNA-ECL detection system based on self-generating coreactants and isothermal amplification. [Display omitted] • A highly sensitive ECL detection method was designed for detection of miRNA based on self-generated coreactant. • Au nanosucculents films was electrodeposited on FTO electrode to improve the conductivity of the sensing interfaces. • The catalyzed hairpin assembly (CHA) reaction leaded to drastic signal amplification. [ABSTRACT FROM AUTHOR]

In vitro screening strategies based on the inhibition of α-glucosidase (GAA) activity have been widely used for the discovery of potential antidiabetic drugs, but they still face some challenges, such as poor enzyme stability, non-reusability and narrow range of applicability. To overcome these limitations, an in vitro screening method based on GAA@GOx@Cu-MOF reactor was developed in our previous study. However, the method was still not satisfactory enough in terms of construction cost, pH stability, organic solvent resistance and reusability. Thence, there is still a great need for the development of in vitro screening methods with lower cost and wider applicability. A colorimetric sensing strategy based on GAA/(Au–Au/IrO 2)@Cu(PABA) cascade catalytic reactor, which constructed through simultaneous encapsulating Au–Au/IrO 2 nanozyme with glucose oxidase-mimicking and peroxidase-mimicking activities and GAA in Cu(PABA) carrier with peroxidase-mimicking activity, was innovatively developed for in vitro screening of GAA inhibitors in this work. It was found that the reactor not only exhibited excellent thermal stability, pH stability, organic solvent resistance, room temperature storage stability, and reusability, but also possessed cascade catalytic performance, with approximately 12.36-fold increased catalytic activity compared to the free system (GAA + Au–Au/IrO 2). Moreover, the in vitro GAA inhibitors screening method based on this reactor demonstrated considerable anti-interference performance and detection sensitivity, with a detection limit of 4.79 nM for acarbose. Meanwhile, the method owned good reliability and accuracy, and has been successfully applied to the in vitro screening of oleanolic acid derivatives as potential GAA inhibitors. This method not only more effectively solved the shortcomings of poor stability, narrow scope of application, and non-reusability of natural enzymes in the classical method compared with our previous work, but also broaden the application scope of Au–Au/IrO 2 nanozyme with glucose oxidase and peroxidase mimicking activities, and Cu(PABA) carrier with peroxidase mimicking activity, which was expected to be a new generation candidate method for GAA inhibitor screening. [Display omitted] • A GAA/(Au–Au/IrO 2)@Cu(PABA) cascade catalytic reactor was developed for in vitro screening of GAA inhibitors. • The reactor exhibits excellent stabilities, reusability and catalytic activity. • A low detection limit of 4.79 nM was obtained for acarbose. • The reactor was successfully applied for the screening of oleanolic acid derivatives as potential GAA inhibitors. [ABSTRACT FROM AUTHOR]

Enzyme cascade with high specificity and catalytic efficiency has significant applications for developing efficient bioanalysis methods. In this work, a sensitive and selective aptasensor was constructed based on the DNA-induced assembly of biocatalytic nanocompartments. Different from the conventional co-immobilization in one pot, the cascade enzymes of glucose oxidase (GOX) and horseradish peroxidase (HRP) were separately encapsulated in ZIF-90 nanoparticles. After conjugating complementary DNA or aptermer on enzyme@ZIF-90, DNA hybridization drove enzyme@ZIF-90 connected into clusters or linked on other DNA modified biocatalytic nanocompartment (such as invertase loaded Fe 3 O 4 @SiO 2). Owing to the shortened distance between enzymes, the catalytic efficiency of connected clusters was significantly enhanced. However, the specifically interaction between the substrate molecule and aptermer sequence would lead to the disassembly of DNA duplexes, resulting in the gradual "switching-off" of cascade reactions. With aflatoxin B1 (AFB1) as the model substrate, the compartmentalized three-enzyme nanoreactors showed good analytical performance in the linear range from 0.01 ng mL−1 to 50 ng mL−1 with a low detection limit (3.3 pg mL−1). In addition, the proposed aptasensor was applied to detect AFB1 in corn oil and wheat powder samples with total recoveries ranging from 94 % to 109 %. As a result, this DNA-induced strategy for enzyme cascade nanoreactors opens new avenues for stimuli-responsive applications in biosensing. [Display omitted] • Catalytic nanocompartments were assembled by DNA-induced strategy. • The catalytic efficiency of connected nanocompartments was largely increased. • The cascade nanoreactors can be switched off after the destroy of DNA duplexes. • DNA-induced assembly was flexible in constructing cascade nanoreactors. • The developed nanoreactors have good analytical performance for aptasensing. [ABSTRACT FROM AUTHOR]

G-quadruplex (G4)/hemin DNAzymes with conversion of substrates into colorimetric readouts are well recognized as convenient biocatalysis tools in sensor development. However, the previously developed colorimetric G4/hemin DNAzymes are diffusive substrate-based DNAzymes (DSBDs). The current colorimetric DSBDs have several drawbacks including high dosage (∼mM) of diffusive substrates (DSs), colorimetric product toxicity, and single colorimetric readout without tolerance to fluctuation of experimental factors and background. In addition, the usage of high-dosage DSs can smear the G4 foldings and their discard is more harmful to environment. Therefore, exploring alternative DNAzymes with potential to overcome these drawbacks of DSBDs is urgently needed. We herein developed associative substrate-based DNAzymes (ASBDs). Cyanine dyes were selected as associative substrates (ASs) due to their binding competency with G4/hemin DNAzymes. With respect to DSBDs, ASBDs needed only low dosage (∼10 μM) of ASs to be able to cause a rapid and visible substrate conversion. In addition, since cyanine dyes are NIR dyes with high extinction coefficients and their conversion products have absorption bands at shorter wavelength. Therefore, a colorimetric ratio response can be developed to follow activities of G4/hemin DNAzymes with competency to tolerate fluctuation of experimental factors and background. In particular, herein developed ASBDs can endure somewhat concentration fluctuation of H 2 O 2. ASBDs are able to cowork with other enzymes (for example, glucose oxidase) to realize cascade sensing. The developed ASBDs can operate at low dosage of substrates with a colorimetric ratio response and can overcome the drawbacks met in DSBDs. We expect that, by designing ASs with fruitful color panel in the future, our work will inspire more interesting in developing environment-benign and low-carbon G4/hemin DNAzymes and desired colorful high-performance sensors. [Display omitted] • G-quadruplex/hemin DNAzymes operating at low-dosage associative substrates (∼μM) is developed. • A ratiometric response of DNAzymes can be achieved using cyanine dyes as the associative substrates. • The developed DNAzymes can be used to monitor the in situ produced low-content H 2 O 2. [ABSTRACT FROM AUTHOR]

This paper reports the development of a highly sensitive and selective electrochemical peptide-based biosensor for the detection of the inflammatory disease biomarker, interleukin-1beta (IL-1β). To this end, flower-like Au–Ag@MoS 2 -rGO nanocomposites were used as the signal amplification platform to achieve a label-free biosensor with a high sensitivity and selectivity. First, a high-affinity peptide for IL-1β was identified through biopanning with M13 random peptide libraries, and was newly designed by incorporating cysteine at the C-terminus. An IL-1β specific binding peptide was used as the bio-receptor, and the interaction between the IL-1β binding peptide and IL-1β was confirmed via enzyme-linked immunosorbent assay and various physicochemical and electrochemical analyses. Under optimal conditions, the biosensor achieved an ultrasensitive and specific IL-1β detection in a wide linear concentration range of 0–250 ng/mL with a picomolar-level detection limit (∼2.4 pM), low binding constant (∼0.62 pM), and a low coefficient of variation (<1.65 %). The biosensor was successfully utilized for IL-1β determination in the serum of Crohn's disease patients with a good correlation coefficient. In addition, the detection performance was comparable to that of commercially available IL-1β ELISA kit. This indicates that the electrochemical peptide-based biosensor may offer a potentially valuable platform for the clinical diagnosis of various inflammatory disease biomarkers. [Display omitted] • A novel affinity peptide-tethered Au–Ag–MoS 2 -rGO nanocomposite electrode for the detection of IL-1β. • The peptide-tethered Au–Ag–MoS 2 -rGO nanocomposite electrode exhibited good conductivity and improved electrochemical activity. • The proposed biosensor has a good linear range with a picomolar detection limit and low coefficient variation. • The detection ability of the developed sensor is comparable to that of a commercial IL-1β ELISA kit. [ABSTRACT FROM AUTHOR]

Recently, the enzymatic cascade reactions during the cellular process are widely used for fabricating robust biosensors and they have attracted extensive attention in analyzing various clinical biomarkers. The enzymatic cascades analysis is commonly based on the peroxidase (POD)/oxidase coupled system. However, the requirement of harsh acidic environment, poor stability and interference from the oxidase further limit their analytical practicability. Herein, novel chromogenic nanomaterials with H 2 O 2 sensitive features are urgently required to replace the POD nanozyme in enzymatic cascades based bioanalysis. Herein, oxygen deficient MoO 3-x with H 2 O 2 sensitive features and near-infrared (NIR) absorption band have been ultra-fast synthesized and utilized for the enzymatic cascades analysis of α-Glucosidase's activity, and inhibitors screening. With the addition of 4-nitrophenyl-α- d -glucopyranoside, the simultaneous presence of α-Glucosidase and glucose oxidase (GO x) would fade their dark blue color and decrease the NIR absorption. The α-Glucosidase's activity can be analyzed by the absorption at 770 nm, and their limit of detection is 8 × 10−5 U/mL, indicating the superior performance of the proposed colorimetric assay. Moreover, this proposed α-Glucosidase assay is further utilized for inhibitors screening. Moreover, the activity of α-Glucosidase can also be analyzed by the smartphone and microplate reader through the agarose-based colorimetric portable kit. This MoO 3-x involved enzymatic cascades assay would facilitate for the development of bio-analysis related to H 2 O 2 generation or consumption. Moreover, this bio-analysis strategy will contribute to the development of other H 2 O 2 sensitive chromogenic nanomaterials for the analysis of certain biomolecules and biological enzymes. [Display omitted] • The ultra-fast synthesis of NAC capped MoO 3-x nanomaterials have been realized. • The α-Glucosidase's activity can be detected by NAC-MoO 3-x with extremely low LOD. • This proposed α-Glucosidase assay can be utilized for screening inhibitors. • NAC-MoO 3-x hold potential for the colorimetric bioanalysis involved with H 2 O 2. [ABSTRACT FROM AUTHOR]

Maillard reaction involves the polymerization, condensation, and other reactions between compounds containing free amino groups and reducing sugars or carbonyl compounds during heat processing. This process endows unique flavors and colors to food, while it can also produce numerous hazards. Acrylamide (AAm) is one of Maillard's hazards with neurotoxicity and carcinogenicity, these effects can trigger mutations and alternations in gene expression in human cells and accelerate organ aging. An accurate and reliable acrylamide detection method with high sensitivity and specificity for future regulatory activities is urgently needed. Herein, we constructed a colorimetric aptasensor with the hybridization of MIL-glucose oxidase (MGzyme)-cDNA and magnetic nanoparticle-aptamer (MNP-Apt) to specifically detect AAm. The incorporation of MB-Apt and AAm released MGzyme-cDNA in the supernatant, took the supernatant out, with the addition of glucose and TMB, MGzyme would oxidize glucose, the resulting •OH facilitated the oxidation of colorless TMB to blue ox-TMB. The absorbance value at 652 nm, which indicates the characteristic absorption peak of ox-TMB, exhibited a proportion to the concentration of AAm. MGzyme avoided the addition of harmful intermediate H 2 O 2 and created an acid microenvironment for the catalytic reaction. MNP-Apt possessed the advantages of high specificity and simplified separation. Under optimal conditions, this method displayed a linear range of 0.01–100 μM with the limit of detection of 1.53 nM. With the spiked analysis data cross-verified by ELISA kit, this aptasensor was proven to specifically detect AAm at low concentrations. This colorimetric aptasensor was the integration of aptamer and the enzyme-cascade system, which could broaden the applicable range of enzyme-cascade system, break the limits of specific detection of substrates, eliminate the need for harmful intermediates, improve the reaction efficiency, implement the specific detection, whilst enabling the accurate detection of AAm. Given these remarkable performances, this method has shown significant potential in the field of food safety inspection. [Display omitted] • Enzyme-cascade system was constructed with GOx and MIL to construct MGzyme-cDNA. • MGzyme-cDNA avoided the addition of H 2 O 2 , MNP-Apt simplified the separation. • Aptamer of AAm made the aptasensor highly specific and interference-resistant. • The method could be applied to real samples like artificial meat, biscuits, etc. [ABSTRACT FROM AUTHOR]

Coronary artery disease (CAD) is the leading cause of death worldwide. Earlier detection of CAD improves treatment outcomes and secondary prevention. The circulating fetuin-B protein is considered to be a promising biomarker for the early detection of CAD. However, a facile and reliable clinical test for fetuin-B is still lacking. Herein, we describe a reliable fluorescent biosensor for detecting fetuin-B in plasma that combines quantum dots-doped polystyrene nanoparticles with an immunochromatographic assay strip (QNPs-ICAS). The QNPs served as detection signals in the QNPs-ICAS sensor system, which was based on a double-antibody sandwich structure. Under optimum experimental conditions, the biosensor exhibited a broad linear range of 1–200 ng mL−1 and a low detection limit of 0.299 ng mL−1. Furthermore, the proposed immunosensor demonstrated high sensitivity, satisfactory selectivity, good reproducibility, and excellent recovery. Finally, the performance and applicability of our QNPs-based ICAS system were validated in clinical samples using a commercial ELISA kit with excellent correlations (r = 0.98451, n = 116). To conclude, the proposed sensor served as a rapid, sensitive, and accurate method for detecting fetuin-B in actual clinical samples, thereby demonstrating its potential for preliminary CAD screening and diagnosis. A reliable fluorescent biosensor for detecting fetuin-B in plasma that combines quantum dots-doped polystyrene nanoparticles with an immunochromatographic assay strip (QNPs-ICAS). The QNPs served as detection signals in the QNPs-ICAS sensor system, which was based on a double-antibody sandwich structure. [Display omitted] • A rapid and sensitive QNPs-ICAS was established for detection of fetuin-B. • The QNPs was used to enhance fluorescence signals and improve detection limit. • A linear dynamic concentration range of 1–200 ng mL−1 with a detection limit of 0.299 ng mL−1 for fetuin-B. • The proposed method exhibited satisfactory selectivity, reproducibility, and recovery. • The sensor was feasible for fetuin-B determination in real samples. [ABSTRACT FROM AUTHOR]

Wearable biosensors have gained huge interest due to their potential for real-time physiological information. The development of a non-invasive blood glucose device is of great interests for health monitoring in reducing the diabetes incidence. Here, we report a sandwich-structured biosensor that is designed for glucose levels detection by using sweat as the means of monitoring. The Prussian blue nanoparticles (PBNPs) and carboxylated carbon nanotubes (MWCNT-COOH) were self-assembled on the electrode to improve the electrochemical performance and as the sensor unit, glucose oxidase (GOx) was immobilized by chitosan (CS) as the reaction catalysis unit, and finally encapsulated with Nafion to ensure a stable performance. As a result, the GOx/PBNPs/MWCNT-COOH sensor displays a low detection limit (7.0 μM), high sensitivity (11.87 μA mM−1 cm−2), and excellent interference resistance for a full sweat glucose application range (0.0–1.0 mM) for both healthy individuals and diabetic patients. Additionally, the glucose sensor exhibits stable stability for two weeks and can be successfully applied to screen-printed carbon electrodes (SPCE), demonstrating its great potential for personalized medical detection and chronic disease management. [Display omitted] • Construction of an intercalated structure biosensor for non-invasive blood glucose monitoring. • Self-assembly technique ensures that sensors advantage of easy batch preparation, low cost and fast detection. • The sensitivity of the sensor was 11.87 μA mM−1 cm−2 with a detection limit as low as 7.0 μM. • This work paving the way for promising prospects in future health monitoring. [ABSTRACT FROM AUTHOR]

It is of great interest and necessity to develop a nonenzymatic, simple but highly sensitive biosensor for early diagnosis of oral cancer. Present here is an electrochemical DNA biosensor which integrates a target-triggered, entropy-driven, nonenzymatic and isothermal amplification strategy with gold nanoparticles/zeolitic imidazolate frameworks-8 (AuNPs@ZIF-8) nanocomposites for ultra-sensitive detection of oral cancer-related biomarker (ORAOV 1) in saliva. It is worth noting that the nuclease is not involved in the whole reaction process, which is simple and flexible in design only using a series of linear single-stranded DNA, avoiding undesired secondary structure interference. Meanwhile, due to the synergistic effect of AuNPs and ZIF-8, AuNPs@ZIF-8 nanocomposites display high stability, excellent electrical conductivity and exceptional electrocatalytic activity, further enhancing the electrochemical signal and avoiding labeling electrochemical signal probes. Experimental results demonstrate that this electrochemical DNA biosensor has a wide linear range (1 fM ∼1 nM), a low limit of detection (163 aM), excellent specificity, superior reproducibility and stability to ORAOV 1. More importantly, the actual application of the newly developed electrochemical biosensor is exemplified in human saliva with satisfactory recoveries. Therefore, the newly developed electrochemical biosensor has a broad application prospect in the nondestructive and early screening of oral cancer. An attomolar-level electrochemical DNA biosensor based on target-triggered and entropy-driven catalytic amplification integrated with AuNPs@ZIF-8 nanocomposites for ultra-sensitive detection of ORAOV 1 in saliva. [Display omitted] • A nonenzymatic and ultra-sensitive electrochemical biosensor for oral cancer overexpressed 1 was established. • A target-triggered and entropy-driven catalytic amplification was employed to amplify the output signals. • Nucleases were not involved, but the limit of detection was as low as 163 aM. • AuNPs@ZIF-8 nanocomposites with excellent electrocatalytic activity were introduced to further enhance signals. [ABSTRACT FROM AUTHOR]

The substrates of oxidase are biologically essential substances that are closely associated with human physiological health. However, current biosensing methods suffer from tough recyclability and undesired denaturation of enzyme due to impurity interference. Herein, we have developed a visual and reusable biosensor for detecting substrate using glucose oxidase (GOx) as a model oxidase. GOx was immobilized onto gold nanoparticles (AuNPs) at −20 °C in one step without additional reagents. The resulting nano-enzyme generated coloimetric signals by coupling with horseradish peroxidase (HRP) using TMB as the substrate. Our results demonstrated that the immobilized GOx exhibited satisfactory sensitivity (0.68 μM) for glucose detection and higher inherent stability than free GOx under harsh conditions, enabling reliable detection of glucose in complex fluids (colored beverages and saliva). Furthermore, the nano-enzyme retained 80 % activity even after four cycles of catalytic oxidation. This strategy constructs a universal biosensor for substrates with nano-enzyme which rely only on intrinsic cysteine within the oxidase while avoiding functional handle modification. A visual and resuable nano-enzyme biosensor was constructed for sensing oxidase substrate, its construction is easy and general through only freezing without requirement of additional reagent, satisfactory activity and good stability were exhibited for substrate sensing. [Display omitted] • A visual and resuable biosensor was developed for sensing oxidase substrate by the construction of nano-enzyme complex. • Oxidase could be immobilized onto AuNPs under freezing condition with just one step and no requirement of additional reagent. • The immobilized oxidase exhibited satisfactory activity and good stability, enabling substrate biosensing in complex fluids. [ABSTRACT FROM AUTHOR]

Development of artificial enzymes, including nanozymes as an alternative for non-stable and expensive natural enzymes, is a booming field of modern Biosensorics and Biofuel Technology. In this study, we describe fabrication and characterization of sensitive biosensors for the detection of ethanol and glucose based on new micro/nanocomposite electrodes with peroxidase-like activity (nanozyme) coupled with microbial oxidases: alcohol oxidase (AOX) and glucose oxidase (GOX). The nanozyme was synthesized by modification of carbon microfibers (CF) by hemin (H) and gold (Au) nanoparticles. The formation of gold nanoparticles on the surface of hemin-modified carbon microfibers has been confirmed by the UV–Vis and X-ray spectroscopy as well by the SEM analysis. Compared to hemin-only modified electrodes, the resulting micro/nanocomposite CF-H-Au electrodes exhibit a higher specific catalytic activity and a better affinity for H 2 O 2 in solution. The H 2 O 2 -sensitive CF-H-Au-modified electrodes showed a higher sensitivity (1.3–2.6-fold) compared with the nearest carbon-derived analogs and were used for the construction of highly sensitive ethanol and glucose biosensors. To eliminate diffusion limitation for substrates, AOX or GOX were fixed on the CF-H-Au-modified electrodes using a highly porous Nafion membrane. The main biosensors' characteristics have been investigated. The developed biosensors were tested for ethanol and glucose analysis in the real samples of both grape must and wine. The results are in good agreement with the results obtained using enzymatic kits as reference approaches. Image 1 • A new micro/nanocomposite with peroxidase-like activity was synthesized. • The nanozyme is based on carbon microfibers modified by hemin and gold nanoparticles. • It was used for construction of highly sensitive ethanol and glucose biosensors. • The biosensors were tested for ethanol and glucose analysis in the real beverages. • The obtained results have a high correlation with the reference approaches. [ABSTRACT FROM AUTHOR]

The tenfold lowering in binding energy for TU-Tyrosine in immobilized urease (K b : 4.7 × 103) with respect to the native enzyme (K b : 6.5 × 104) begets easy desorption of thiourea (TU) by glucose (GL) with an eventual formation of a more strong TU- GL adduct; that rejuvenates the kit-material ready for the subsequent cycle(s). The sorption-desorption heeds fluorescence turn-off and turn-on in DCM for selective sensing of TU- GL pair at their respective linear range of concentration 2.5–26.1 ppm and 2.36–11.57 ppm. The process was found to be static (K SV ≥ 2.25 × 103 L mol−1), exothermic (ΔH: -0.08 kJ mol−1), spontaneous (ΔG: -21.1 kJ mol−1) and marginally entropy gaining (ΔS: 0.07 kJ mol−1 K−1). The 'bulk material' (200 ± 20 μm) brilliantly preconcentrates TU with an enrichment factor of 106.2 after its selective extraction at near-neutral pH from a large volume sample (800 mL) of low concentration (30 ppm). A very dilute solution (0.05 mmol L−1) of GL at minimum volume (6 mL) acts as a stripping agent and provides a longer life (200 cycles with good extraction efficiency) to the material. The method was found to be efficient in the analysis of fruit juice as a real sample. Sorption-desorption heeds fluorescence 'turn off – turn on' performance at 'Urease immobilized single kit' for micro level detection of Thiourea-Glucose pair. Image 1 [ABSTRACT FROM AUTHOR]

Background: Fluorescence immunoassays are commonly employed for the detection of pathogenic bacteria as a means of ensuring food safety and preserving public health. However, the challenges such as poor photostability and background interference have limited their sensitivity and accuracy. The emergence of metal-organic frameworks (MOFs) as a label probe offers a promising solution for advancing fluorescence immunoassays owing to their tunable nature. Nonetheless, the low fluorescence efficiency of MOFs and the potential risk of dye leakage pose obstacles to achieving high detection sensitivity. Therefore, there exists a pressing need to fully utilize the potential of MOF composites in fluorescence immunoassays., Results: We explored the potential of glucose oxidase-encapsulated zeolitic imidazole framework-90 (GOx@ZIF-90) as a label probe to construct a time-resolved fluorescence immunoassay with amplified detection signal. This immunoassay involved functionalizing Fe 3 O 4 nanoparticle with porcine antibody to specifically capture and separate the target bacteria, Staphylococcus aureus (S. aureus). The captured S. aureus was then bound by GOx@ZIF-90 modified with vancomycin, resulting in a fluorescence response in the europium tetracycline (EuTc). The encapsulation of GOx in ZIF-90 provided a confinement effect that significantly enhanced the catalytic activity and stability of GOx. This led to a highly efficient conversion of glucose to H 2 O 2 , amplifying the fluorescence signal of EuTc. The immunoassay demonstrated a high sensitivity in detecting S. aureus, with a detection limit of 2 CFU/mL. We also obtained satisfactory results in milk samples. Attractively, the time-resolved detection mode of EuTc allowed the immunoassay to eliminate background fluorescence and enhance accuracy., Significance: This study not only presented a new method for detecting foodborne pathogens but also highlighted the potential of enzyme-encapsulated MOF composites as label probes in immunoassays, providing valuable insights for the design and fabrication of MOF composites for various applications., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2023 Elsevier B.V. All rights reserved.)

Enzyme cascade reactions can greatly improve catalytic efficiency and achieve selective and sensitive detection of targets. This paper presents a novel strategy for colorimetric sensing of targets by loading natural enzymes into a hemin-doped G-quadruplex (G4-hemin) biohydrogel to form a flexible enzyme cascade sensing (FECS) platform. The biohydrogel has advantages of biocompatibility, printability and flexibility. The biohydrogel not only participates in the cascade reaction as the mimic enzyme but also provides a mild microenvironment for the natural enzyme. The FECS platform has a linear range from 0.4 μM to 120 μM and a detection limit of 3.6 × 10−6 M for hydrogen peroxide detection. Additionally, the FECS platform has a low detection limit and wide linear range for glucose and xanthine by loading xanthine oxidase (XOD) and glucose oxidase (GOD) into the biohydrogel, respectively. These results indicate that the novel FECS platform is an effective detection platform that can detect multiple targets and is expected to be widely used in flexible sensing. Image 1 • A flexible enzyme cascade sensing (FECS) platform for targets sensing. • FECS platform is based on G4-hemin biohydrogel and natural enzyme. • The biohydrogel has peroxidase-like activity and biocompatibility. • The biohydrogel has network porous structure for loading enzyme. • H 2 O 2 , xanthine and glucose can be detected with great performances. [ABSTRACT FROM AUTHOR]

Point-of-care (POC) diagnostic devices play significant roles in delivering vital surveillance information and providing proper and timely care to patients. There is a challenge in the development of new diagnostic tools to overcome their current shortcomings in terms of cost issues, accuracy and performance. Herein, a highly efficient paper-based analytical device based on a 2D metal-organic framework (MOF) has been reported for the colorimetric/fluorometric monitoring of glucose. Because of the inherent bifunctional activity of cobalt-terephthalate MOF (CoMOF) nanosheets, great improvements were made to the stability and performance of glucose oxidase (GOX) and to its catalytic effect on the reaction of o-phenylenediamine (OPD) and H 2 O 2. The exceptional behavior of 2D CoMOF, along with a precise smartphone readout, led to the rapid and sensitive colorimetric/fluorometric detection of glucose in biological samples. Paper modified by CoMOF and GOX was stable for a long time, and a yellow-brown color and a high fluorescence emission were observed after the addition of a low volume of sample and OPD solutions. The probe showed a wide linear effectiveness range of 50 μM-15 mM, with colorimetric and fluorometric detection limits of 16.3 and 3.2 μM, respectively. Despite its great simplicity, the developed probe showed high performance and accuracy for the quantification of glucose. Image 1 • Exceptional bifunctional activity of 2D cobalt metal-organic framework (CoMOF). • Notable enhancement of the stability and performance of GOX on the paper by CoMOF. • Superb catalyzing effect of CoMOF on the dissociation of H 2 O 2 to hydroxyl radicals. • Development of paper-based diagnostic assay for glucose monitoring in blood. • Recording of colorimetric/fluorometric signals by smartphone readout. [ABSTRACT FROM AUTHOR]

In this research, microfluidic paper distance-based systems for the quantification of redox species are proposed. For the preparation of the sensing zone a Prussian Blue (PB) (convertible to Prussian White (PW)) layer was deposited in the channel manufactured by wax-printing technique. According to the chemical properties of PB/PW system, it is possible to develop optical sensors sensitive to both oxidizing and reducing agents. The created systems were evaluated for the determination of ascorbic acid and hydrogen peroxide, which were chosen and used as model analytes. The final versions of the proposed systems exhibited a linear response from 0.25 mmol L−1 to 4.0 and 2.0 mmol L−1 for ascorbic acid and H 2 O 2, respectively. The analytical utility of the paper systems was confirmed by measuring the levels of ascorbic acid in dietary supplements. Results correlation obtained for the described systems and the reference method was over 0.98 (Pearson's R-coefficient). All measurements were characterized by satisfactory reproducibility and acceptable uncertainty (RSD (%) < 6%). Finally, it was demonstrated that the modification of the PW-strip systems with oxidoreductase led to an enzymatic assay for glucose up to 10 mmol L−1 range. Practical utility of the developed bio-strips was confirmed by quantifying glucose in drinks and dietary supplement samples. Image 1 • Distance-based μPADs sensitive to ascorbic acid and hydrogen peroxide are introduced. • Prussian Blue sensing layer was used as a chemoreceptor in working area of the μPADs. • Biomodification of systems with glucose oxidase leads to sensor for glucose. • A successful determination of glucose and ascorbic acid in real samples are performed. • Obtained results for quantification of analytes of interests highly correlates with reference methods. [ABSTRACT FROM AUTHOR]

Colorimetric sandwich-type biosensors that can both provide sensitivity competitive with fluorescence-based approaches, and leverage reagents that are cost-effective, widely available and as safe as possible, are highly sought after. Herein, we demonstrate an alternative highly-sensitive colorimetric method for paper-based sandwich-type biosensing that uses starch–iodide complexation to simplify practical biosensing using ubiquitous reagents. Targeting the mycotoxin ochratoxin A (OTA), a covalently-immobilised OTA antibody on a cellulose surface captures OTA and forms a sandwich with OTA aptamer-conjugated glucose oxidase. Adding the chromogenic reagents at an optimized concentration, a distinct blue color develops within 30 min, offering excellent contrast with the clear/white of the negative sample. With a sampling volume down to just 5 μL, the assay exhibits concentration limits of detection and quantitation of 20 and 320 pg mL−1, respectively, and a linear range from 10−1 to 105 ng mL−1 (R2 = 0.997). The method displays excellent selectivity against related mycotoxins, excellent %recovery (95–117%) and robust operation in complex matrices (beer, urine and human serum), with no significant difference versus gold-standard liquid chromatography. Along with its excellent analytical performance, this assay benefits from non-toxic and extremely cheap reagents that can be safely disposed of in the field, and presents an attractive alternative to toxic dyes and nanoparticles. Image 1 • Novel colorimetric antibody-aptamer sandwich assay using starch-iodine complexation. • Central composite design for fast and efficient sensor optimization. • Ultrasensitive detection of OTA using PADs with LoD of 20 pg mL−1 using 5 μL. • Applied for OTA detection in beverages, urine and human serum. [ABSTRACT FROM AUTHOR]

In the review, the principles and main purposes of using multienzyme systems in electrochemical biosensors are analyzed. Coupling several enzymes allows an extension of the spectrum of detectable substances, an increase in the biosensor sensitivity (in some cases, by several orders of magnitude), and an improvement of the biosensor selectivity, as showed on the examples of amperometric, potentiometric, and conductometric biosensors. The biosensors based on cascade, cyclic and competitive enzyme systems are described alongside principles of function, advantages, disadvantages and practical use for real sample analyses in various application areas (food production and quality control, clinical diagnostics, environmental monitoring). The complications and restrictions regarding the development of multienzyme biosensors are evaluated. The recommendations on the reasonability of elaboration of novel multienzyme biosensors are given. Image 1 • Biosensors based on cascade, cyclic and competitive enzyme systems are described. • Advantages and limitations of multienzyme electrochemical biosensors are analyzed. • Multienzyme systems allow an extension of the spectrum of detectable substances. • An improvement of the biosensor sensitivity and selectivity is possible. [ABSTRACT FROM AUTHOR]

Blood glucose measurement plays a very important role in clinical diagnosis and fluorescence analysis has attracted extensive attention. A novel ratiometric fluorescent system with aggregation induced emission (AIE) property for the detection of glucose was established in this work. In this system, bovine serum albumin-stabilized Au nanoclusters (BSA-AuNCs) served both as the fluorescent detection probe and the AIE inducer. An AIE molecule, named sodium 1,2-bis [4-(3-sulfonatopropoxyl) phenyl]-1,2-diphenylethene (BSPOTPE), served as fluorescent reference probe. In the presence of H 2 O 2 , the fluorescence intensity of BSPOTPE/BSA-Au NCs at 680 nm progressively decreased while that at 490 nm remained constant. Glucose can be catalyzed by glucose oxidase (GOx) and produces H 2 O 2. Therefore, glucose detection can be conveniently achieved by the proposed strategy. The fluorescence intensity change ratio increased linearly with the glucose concentration in the range 1–8 mM. Moreover, the proposed method exhibits a consecutive fluorescence color change ("from red to cyan") to glucose concentration in the range of 1–8 mM under a 365 nm UV lamp and exhibits bright "red" or bright "cyan" in lower glucose concentrations (lower than 3 mM) or high glucose concentrations (higher than 7 mM), respectively. The work offers an ideal rapid clinical diagnostic method for both normal and abnormal blood glucose screening. Image 1 • An ratiometric fluorescent probe based on BSA-AuNCs induced AIE was fabricated. • BSA-AuNCs and BSPOTPE served as detection and reference probe, respectively. • Due to H 2 O 2 -induced oxidation on AuNCs, the probe was applied for sensing of H 2 O 2. • By detecting the production H 2 O 2 , Glucose can be detected through GOx catalyzing. • A rapid screening method of glucose was established based on the color change. [ABSTRACT FROM AUTHOR]

A novel 3D paper-based microfluidic screen-printed electrode (SPE) composed of two layers was constructed by photolithography and screen-printing technology. Aldehyde functionalized hydrophilic zone of the counter and reference electrodes layer was prepared for glucose oxidase immobilization. Highly conductive prussian blue deposited reduced graphene oxide-tetraethylene pentamine (rGO-TEPA/PB) modified paper working electrode layer can be used as an electrochemical sensitive membrane for quantitative detection of hydrogen peroxide (H 2 O 2), which was the enzyme-catalyzed reaction product. Therefore, this 3D paper-based microfluidic electrochemical biosensor can be used for quantitative detection of glucose. Under optimum conditions, the proposed biosensor can be used for quantitative determination of glucose over a wide linear range of 0.1 mM–25 mM with detection limit of 25 μM. Finally, the 3D paper-based microfluidic electrochemical biosensor was applied to determine glucose in human sweat and blood, and the obtained results were in good consistency with values measured by Roche's blood glucose meter. In addition, the proposed 3D paper-based electrochemical device showed good repeatability, stability, and anti-interference, which would be of great potential to monitor glucose in complex biological fluids. A novel 3D paper-based microfluidic screen-printed electrode composed of two layers was constructed by photolithography and screen printing technology. Aldehyde functionalized hydrophilic zone of the counter and reference electrodes layer was prepared for glucose oxidase immobilization. Highly conductive Prussian blue deposited reduced graphene oxide-tetraethylene pentamine modified paper working electrode layer can be used as an electrochemical sensitive membrane for quantitative detection of H 2 O 2 , which was the enzyme-catalyzed reaction product. Therefore, this 3D paper-based microfluidic electrochemical biosensor can be used for quantitative detection of glucose. Under optimum conditions, the proposed biosensor can be used for quantitative determination of glucose over a wide linear range of 0.1 mM–25 mM with detection limit of 25 μM. Image 1 • A paper based electrochemical approach for the determination of glucose is presented. • Enhanced stability, good selectivity, outstanding simplicity and low-cost biosensor. • Validation with the determination of glucose in human sweat and blood shows very good results. [ABSTRACT FROM AUTHOR]

In this paper, horseradish peroxidase (HRP) was successfully immobilized on heated Au disk electrode (HAuDE) by biotin-streptavidin specific interaction through HS-ssDNA-biotin self-assembled on HAuDE for investigation the electrocatalytic activity of HRP. With elevated electrode temperature, the significant temperature effect of the electrocatalytic activity of HRP for H 2 O 2 reduction was demonstrated by using this bio-sensing platform. With an electrode temperature of 40 °C, a detection limit of 1.5 × 10−6 mol L−1 for H 2 O 2 reduction could be obtained, which was more than one magnitude lower than that with an electrode temperature of 0 °C. Because HRP can be widely used as an enzyme label for amplification detection, this sensing platform can be broadly applied to analytical chemistry such as nucleic acid detection, and aptamer-based biosensors. Image 1 • HRP was immobilized on HAuDE by biotin-streptavidin specific interaction. • The temperature effect of the electrocatalytic activity of HRP was demonstrated. • With an electrode temperature of 40 °C, the detection limit for H 2 O 2 was more than one magnitude lower than that with 0 °C. • This method can be broadly applied to analytical chemistry because HRP can be used as an enzyme label. [ABSTRACT FROM AUTHOR]

Herein we present a general and turn-on strategy for enzymatic bioassays on the basis of redox state dependent emission of gold nanoclusters (AuNCs). The photoluminescence of AuNCs was quenched obviously by the oxidative ferricyanide while unaffected by its corresponding reduced state, i.e., ferrocyanide. The distinctive quenching abilities for AuNCs by the redox couple (ferricyanide/ferrocyanide) enabled their utility as new fluorescent sensing platforms to detect redox-related phenomena. The proposed protocols were conducted by using the model oxidoreductases of glucose oxidase (GOx) and the enzyme cascade of lactate dehydrogenase (LDH)/diaphorase to catalytically convert ferricyanide to ferrocyanide, which switched on fluorescence of the detection systems. The detection limit for glucose and lactate was found to be as low as 0.12 and 0.09 μM, respectively. This work features the first use of the redox couple of ferricyanide/ferrocyanide in fluorescent bioanalysis, which enables versatile, signal on and highly sensitive/selective detections as compared to the state of the art fluorescently enzymatic sensing platforms. Importantly, considering the significance of ferricyanide/ferrocyanide involves in numerous other oxidoreductases mediated biocatalysis, this protocol has wide versatility that enables combination with oxidoreductases related reactions for biosensing. Image 1 • The redox couple of ferricyanide/ferrocyanide is firstly applied to fluorescent bioanalysis. • This work enables signal on detections as compared to other quenched enzymatic bioassays. • It has generality and wide versatility for various enzyme-mediated bioanalysis. [ABSTRACT FROM AUTHOR]

Efficient strategies in enhancing sensitivity are pivotal to ultrasensitive detection of tumor markers. In this work, based on the strategy of label-assisted chemical adsorption triggered conversion of electroactivity of sensing interface, a Ag/AgCl process was achieved to enhance sensitivity of the constructed sandwich-type amperometric immunosensor for ultrasensitive detection of carbohydrate antigen 19–9 (CA19-9). Briefly, polydopamine-Ag nanoparticles (PDA-Ag NPs), as signal precursor, combined with labeling antibody were served as labels and graphene oxide-melamine (GO-MA) substrate with chemical absorption capacity was applied as smart sensing interface. After successfully incubating labels, there was primitively no current response due to the poor conductivity between labels and electrode. However, in the presence of H 2 O 2 , Ag NPs from labels can be etched into Ag ions, which were adsorbed by GO-MA to form GO-MA-Ag as electroactive substrate. Then, the substrate exhibited a sharp and stable electrochemistry peak of solid-state Ag/AgCl process in the buffer containing KCl. The sensitivity toward detection of CA19-9 was notably enhanced based on the appearance of sharp peak. Under optimum conditions, the designed immunosensor demonstrated a wide working range from 0.0001 to 100 U mL−1 and an ultralow detection limit 0.032 mU mL−1. Thus, utilizing this strategy to construct immunosensor was highly promising in clinical diagnosis for ultrasensitive detection of tumor makers. Image 1 • GO-MA composite for chemosorption of Ag+ was used as smart sensing interface. • Ag/AgCl electrochemical process was realized via label-assisted chemosorption. • The immunosensor showed ultralow limit of detection 0.032 mU mL−1 for CA19-9. [ABSTRACT FROM AUTHOR]

By using PbS–Au heterodimers as the signal quencher, TiO 2 /BiOI as matrix, a novel sandwich-type photoeletrochemical (PEC) biosensor for sensitive determination of amyloid β-protein (Aβ, ∼4 KDa) was developed. BiOI was attached to the surface of TiO 2 and formed a heterogeneous structure (p-n junction), which enlarged the light harvest range and enhanced the electron transfer rate of TiO 2. In order to quench the PEC signal, PbS–Au heterodimers were used as the labels to combine with Aβ. Owing to the competitively light energy harvesting and electron donor consuming effect of PbS–Au heterodimers, less light energy and electron donor arrived at TiO 2 /BiOI. In addition, Au directly contacted with PbS could enhance the electron seperation and transfer rate, and lead to improved competitiveness consumption of the electron donor. PbS–Au integrated with secondary antibodies formed PbS–Au-Ab 2 bioconjugate, which would further obstruct the electron transfer and impede the interreaction between electron donor and photoelectrode surfaces. Owing to the unique PbS–Au heterodimer structure and the quenching effect of PbS–Au-Ab 2 bioconjugate, the fabricated immunosensor for Aβ detection exhibited good stability, high sensitivity, and a low detection limit of 0.028 pg/mL (S/N = 3). Image 1 • PbS–Au heterodimers were used as novel signal quencher to quench the PEC signal of TiO 2 /BiOI heterostructure (p-n). • The Au in PbS–Au heterodimers could expedite the electron separation/transfer process and connected with Ab 2. • The biosensor showed a low LOD of 0.028 pg/mL and a wide detection range of 0.0001–500 ng/mL. [ABSTRACT FROM AUTHOR]

Nanozymes have emerged as promising alternatives to overcome the high cost and low stability issues of natural enzymes. Particularly, those with peroxidase-like activities have been extensively studied to construct versatile biosensors. In this article, we demonstrate that the modification of the graphitic carbon nitride nanosheets (g-C 3 N 4 nanosheets) by plasmonic gold nanoparticles (AuNPs) greatly enhances its catalytic performance as peroxidase mimetic. In the presence of H 2 O 2 , the AuNPs@g-C 3 N 4 nanosheets can catalyze the redox reaction of 3,3′,5,5′- tetramethylbenzidine (TMB) to produce a blue color. Based on the observation, a colorimetric sensing method for glucose is further developed with the assistance of glucose oxidase (GOx). The linear range for glucose is from 5 to 100 μmol L−1 (R2 = 0.9967) and the limit of detection (LOD) is 1.2 μmol L−1. The LOD can be further lowered down to 0.75 μmol L−1 by using H 2 SO 4 as termination agent and measuring the absorbance of the yellow product at λ = 451 nm. Moreover, the practical usefulness of AuNPs@g-C 3 N 4 nanosheets as a peroxidase nanozyme for glucose determination in human serum and urine is also demonstrated. • A hybrid catalyst consisting of "naked" Au-NPs grown in situ on g-C 3 N 4 nanosheets was constructed. • Based on its peroxidase-like activity, a sensitive glucose detection method was developed. • The catalytic activity of the AuNPs modified g-C 3 N 4 nanosheets is higher than that of either g-C 3 N 4 nanosheets or AuNPs. [ABSTRACT FROM AUTHOR]

Considering the high incidence level and mortality rate of ovarian cancer, particularly among the European female population, the carbohydrate antigen 125 (CA-125) was selected as the protein target for this study for the development of a MIP-based biosensor. This work presents the development of molecular imprinting polymers (MIPs) on gold electrode surface for CA-125 biomarker recognition. The preparation of the CA-125 imprinting was obtained by electropolymerization of pyrrole (Py) monomer in a gold electrode using cyclic voltammetry (CV) in order to obtain highly selective materials with great molecular recognition capability. The quantification of CA-125 biomarker was made through the comparison of two methods: electrochemical (square wave voltammetry -SWV) and optical transduction (surface plasmon resonance -SPR). SWV has been widely used in biological molecules analysis since it is a fast and sensitive technique. In turn, SPR is a non-destructive optical technique that provides high-quality analytical data of CA-125 biomarker interactions with MIP. Several analytical parameters, such as sensitivity, linear response interval, and detection limit were determined to proceed to the performance evaluation of the electrochemical and optical transduction used in the development of the CA-125 biosensor. The biosensor based in the electrochemical transduction was the one that presented the best analytical parameters, yielding a good selectivity and a detection limit (LOD) of 0.01 U/mL, providing a linear concentration range between 0.01 and 500 U/mL. This electrochemical biosensor was selected for the study and it was successfully applied in the CA-125 analysis in artificial serum samples with recovery rates ranging from 91 to 105% with an average relative error of 5.8%. Image 1 • MIP@AuSPE biosensor for fast CA-125 detection in point-of-care. • Comparison between electrochemical and optical (SPR) sensor. • MIP sensor for a low detection limit of biomolecules with high molecular weight. • Determination of CA-125 in serum at clinically relevant levels (LOD = 0.1 U/mL). [ABSTRACT FROM AUTHOR]

In this work, we found that polyethyleneimine (PEI), a widely applied organic high-molecular polymer, could act as a new co-reactant to obviously improve the electrochemiluminescence (ECL) of S 2 O 8 2−-O 2 system. And owing to its abundant amine groups in the polymeric structure, PEI was further used to covalently crosslink with massive L -cysteine (L -Cys), an effective co-reactant of S 2 O 8 2−-O 2 ECL system, to obtain a new co-reactive high-molecular polymer (PEI- L -Cys) with higher co-reaction efficiency. As loading platform, hierarchically branched Au/Pd dendrimers (Au/Pd DRs G 2) were prepared to immoblize the obtained PEI- L -Cys, detection antibody, and bolocking reagent glucose oxidase (GOD). With the existence of target carcinoembryonicantigen (CEA), an ECL immunosensor was constructed through the sandwiched immunoreaction between the capture antibody on the electrode and the bioconjugate based on Au/Pd DRs G 2. Besides the high enhancement of PEI- L -Cys, the ECL signal was also greatly increased by the dual catalysis to generate O 2 in situ around the electrode induced by the synergistic effect of GOD and Au/Pd DRs G 2 in presence with D -glucose. Especially, due to the special hierarchically branched bimetallic structure, the Au/Pd DRs G 2 had more excellent catalytic effect to H 2 O 2 decomposition in this process. As a result, the proposed ECL immunosensor realized the ultrasensitive detection of CEA, which could provide meaningful reference to the prevention and treatment of related disease. Image 1 • PEI was used as a new co-reactant to obviously improve the ECL of S 2 O 8 2−-O 2 system. • The prepared high-molecular polymer PEI- L -Cys had more outstanding co-reactive efficiency. • The dual catalysis to generate O 2 in situ induced by GOD and Au/Pd DRs G 2 enhanced the sensitivity. • The immunosensor realized the measurement of CEA with ultra-sensitivity. [ABSTRACT FROM AUTHOR]

Ultrathin two-dimensional (2D) metal-organic framework (MOF) nanosheets have attracted numerous attention due to their unparalleled advantages such as unique structures, large surface areas, good stability and high catalytic efficiency. In this paper, 2D Cu(bpy) 2 (OTf) 2 nanosheets (Cu-MOF, bpy = 4,4-bipyridine, OTf = trifluoromethanesulfonate) are first utilized to achieve the fluorescent detection for H 2 O 2 and glucose with their intrinsic peroxidase-like activity. The fluorescent biosensor Cu-MOF nanosheets were achieved by the efficient catalysis of non-fluorescent thiamine (TH) to strong fluorescent thiochrome in the presence of H 2 O 2. With the combination of glucose oxidase, highly selective and sensitive fluorescent detection for glucose could be established with a detection limit of 0.41 μM and two separate linear ranges of 10–100 μM and 100–1000 μM, respectively. Furthermore, the developed method has been applied to human serum for the quantitative determination of glucose as a clinical diagnosis indicator of diabetes mellitus. Image 1 • Two-Dimensional Cu(bpy) 2 (OTf) 2 metal-organic framework nanosheets are first utilized to achieve the fluorescent detection for H 2 O 2 and glucose with their intrinsic peroxidase-like activity. • Non-fluorescent thiamine is converted to intense fluorescent thiochrome by Cu(bpy) 2 (OTf) 2 nanosheets in the presence of H 2 O 2 for selective and sensitive detection of glucose with the combination of glucose oxidase. • The fluorescent biosensor 2-D Cu(bpy) 2 (OTf) 2 nanosheets is developed with detection limit as low as 0.32 μM for H 2 O 2 and 0.41 μM for glucose, respectively. • Quantitative determination of glucose for human serum is established for the diabetic and healthy serum samples. [ABSTRACT FROM AUTHOR]

Development of high-precision human epidermal growth factor receptor 2 (HER2) assay is essential for the early diagnostic and prevention of breast cancer. In this work, an innovative Fe/Mn bimetallic nanozyme at the edge of N-doped carbon defects (FeMn-NC edge) with abundant active sites was prepared through the hydrothermal synthetic method. FeMn-NC edge nanozyme displayed excellent peroxidase-like activity relative to the H 2 O 2 -catalyzed 3,3′,5,5′-tetramethylbenzidine (TMB) system for generation of the oxidized TMB (oxTMB). As a proof-of-concept application, we constructed an electrochemical immunoassay for the detection of HER2 based on the unique merits of FeMn-NC edge. Initially, a sandwiched immunoreaction was carried out in the microtiter plate coated with monoclonal anti-HER2 capture antibodies using glucose oxidase (GOx)-labeled anti-HER2 as detection antibody. The carried GOx could catalyze glucose to produce H 2 O 2 , thus resulting in the formation of oxTMB with the assistance of TMB and FeMn-NC edge nanozyme. The produced oxTMB could be determined on the electrode by the chronoamperometry at an applied potential of +10 mV. Experimental results revealed that the steady-state current increased with the increasing HER2 concentration in the sample, and gave a good linear relationship within the dynamic range of 0.01–10 ng/mL at a limit of detection of 5.4 pg/mL HER2. In addition, good reproducibility, high specificity and acceptable accuracy were acquired for the measurement of human serum samples. Importantly, this method can be extended for quantitative monitoring other disease-related proteins by changing the corresponding antibodies. [Display omitted] • An amplified electrochemical immunoassay was designed to detect human epidermal growth factor receptor 2. • Edge-generated N-doped mesoporous carbon for supporting dual metal active sites. • Bimetallic Fe/Mn edged N-doped carbon used as the nanozyme. • Etching of N-doped carbon using H 2 O 2 to form defect edges with abundant active sites. • Synergistic interaction between bimetals to improve the catalytic performance of nanozymes. [ABSTRACT FROM AUTHOR]

Development of highly sensitive and accurate biosensors still faces a great challenge. Herein, glucose oxidase (GOx) is efficiently immobilized on the AuCu hydrogels owing to their porous structure and interfacial interaction, demonstrating enhanced catalytic activity, satisfactory stability and recyclability. Besides, by integration of AuCu@GOx and electrochromic material of Prussian blue, a sensitive and stable biosensing platform based on the excellent electrochromic property of Prussian blue and the enhanced enzyme activity of AuCu@GOx is developed, which enables the electrochemical and visual dual-mode detection of glucose. The as-constructed biosensing platform possesses a wide linear range, and good selectivity for glucose detection with a limit of detection of 0.82 μM in visual mode and 0.84 μM in electrochemical mode. This easy-to-operate biosensing platform opens a door for the practical application of the multi-mode strategy for glucose detection. [Display omitted] • AuCu hydrogels with porous structure can immobilize glucose oxidase with enhanced catalytic activity and stability. • A biosensing platform is developed based on the electrochromic property and enhanced enzyme activity • An electrochemical and visual detection strategy is used for glucose biosensing. [ABSTRACT FROM AUTHOR]

Biomarkers are the most sensitive reactants and early indicators of many kinds of diseases. The development of highly sensitive and simple techniques to quantify them is challenging. In this study, based on rolling cycle amplification (RCA) and the Nicked PAM/CRISPR-Cas12a system (RNPC) as a signal reporter, a sandwich-type method was developed using antibody@magnetic beads and aptamer for the high-sensitive detection of the C-reactive protein (CRP). The antibody-antigen (target)-aptamer sandwich-like reaction was coupled to RCA, which can produce hundreds of similar binding sites and are discriminated by CRISPR/Cas12a for signal amplification. The ultrasensitivity is achieved based on the dual-signal enhancing strategy, which involves the special recognition of aptamers, RCA, and trans -cleavage of CRISPR/Cas12a. By incorporating the CRISPR/Cas12a system with cleaved PAM, the nonspecific amplification of the RCA reaction alone was greatly reduced, and the dual signal output of RCA and Cas12a improved the detection sensitivity. Our assay can be performed only in two steps. The first step takes only 20 min of target capture, followed by a one-pot reaction, where the target concentration can be obtained by fluorescence values as long as there are 37 °C reaction conditions. Under optimal conditions, this system detected CRP with high sensitivity. The fabricated biosensor showed detection limits of 0.40 pg/mL in phosphate-buffered saline and 0.73 pg/mL in diluted human serum and a broad linear dynamic range of 1.28 pg/mL to 100 ng/mL within a total readout time of 90 min. The method could be used to perform multi-step signal amplification, which can help in the ultrasensitive detection of other proteins. Overall, the proposed biosensor might be used as an immunosensor biosensor platform. [Display omitted] • The clever combination of magnetic beads, aptamers and rolled loop amplification improves sensitivity. • Three Designed ssDNA are combined with RCA products to bring the split PAM together to Initiate Cas12a activity. • High sensitivity, high specificity, short detection time, simple operation. • The detection limit in buffer is 0.40 pg/mL. The detection limit in serum is 0.73 pg/mL. [ABSTRACT FROM AUTHOR]

The self-powered sensor (SPS) is a sensor method that does not require the external power source and has the potential for portable detection of environmental contaminants. In this work, for the first time, a biomolecule-free SPS for detection of ultra-trace triazine endocrine disruptor atrazine (ATZ) with high sensitivity and selectivity is constructed using a glucose oxidase (GOD)-like cobalt metal-organic framework (Co-MOF) nanozyme-modified high-performance anode and a molecularly imprinted cathode. By modulating the size and morphology of the prepared materials, Co-MOF nanozyme with superior GOD-like property (Michaelis constant K m = 15.8 mM) has been obtained and modified at the anode to catalyze glucose oxidation with high efficiency and provide energy continuously and stably for the SPS. The separation mode of anodic energy supply-cathodic recognition ensures the recognition effect without affecting the catalytic characteristic of Co-MOF and the output signal of the SPS. The designed SPS has a wide linear range of 1 pM–100 nM and a detection limit as low as 0.65 pM, as well as superior selectivity and good stability. The present work provides a promising approach for the design of self-powered sensors which can be extended to detection of a wider range of environmental pollutants. The glucose oxidase-like Co-MOF nanozyme has been obtained and applied to the anode with molecularly imprinted cathode as the recognition element, thus the biomolecule-free self-powered sensor has been successfully constructed for sensitive and selective detection of atrazine. [Display omitted] • The Co-MOF nanozyme with superior glucose oxidase-like catalytic activity has been obtained. • The biomolecule-free self-powered sensor has outstanding stability and suitability. • The self-powered sensor achieves highly sensitive and selective detection of atrazine. • The biomolecule-free self-powered sensor has excellent detection performance in actual water sample. • This research provides an efficient design of self-powered sensors. [ABSTRACT FROM AUTHOR]

Diabetes and diabetic wound management have always been urgent issues for global healthcare. In the demand for blood glucose monitoring and wound management, phenylboronic acid (PBA)-based glucose biosensors are effective assistance due to their excellent glucose specificity, high sensitivity, and response stability. Nevertheless, PBA-based glucose biosensors still have challenges in terms of wide linearity and large deformation requirements. Therefore, it is necessary to develop PBA-based glucose biosensors with satisfactory mechanical properties, high response sensitivity, excellent stability, and wide linearity. In this work, a glucose-responsive PBA-based biosensor was successfully synthesized for the first time. The sensor materials exhibited excellent mechanical properties with an elongation at break reached up to 1000%, and the healing efficiency was over 90% within 30 min at 45 °C. Furthermore, the biosensor exhibited exceptional electromechanical responsiveness, stability, high sensitivity, and wide linearity due to the specificity of phenylboronic acid to glucose and the construction of a special HCNT/PEDOT:PSS dual conductive structure. In addition, the assembled biosensor displayed remarkable glucose, pH and temperature responses, exhibiting a linear response to glucose concentration range from 0.20 mM to 2.0 mM, with a sensitivity coefficient of 47.11 mA mM−1 and regression coefficient of 0.942. Moreover, the sensor materials showed satisfactory cytocompatibility, hemocompatibility, and antibacterial properties against Escherichia coli and Staphylococcus aureus. For the first time, a dual conductive structural glucose biosensor based on PBA-based copolymer was synthesized. In addition to excellent glucose sensitivity and response stability, the biosensor has a wide linearity range, excellent self-healing property, and satisfactory mechanical performance. As a promising substitute for non-enzymatic glucose biosensors, this new material with special structure and characteristics would also be beneficial to wound management in diabetic patients. [Display omitted] • The prepared PBA-based PEA copolymers are specific to glucose. • A dual-conductive structure was constructed in the PEA copolymer. • The biosensor possessed linear response to glucose and temperature. • The biosensor exhibited a lower limit of detection. • The biosensor exhibited outstanding biocompatibility and antibacterial property. [ABSTRACT FROM AUTHOR]

The ultrasensitive bioassays are increasingly demanded for disease diagnosis and environmental monitoring. The combined unique natures of the components in nanocomposites have led to their wide applications in bioanalysis. In the current study, a simple strategy for preparing polyethyleneimine-functionalized reduced graphene oxide-hemin-bovine serum albumin (PEI-rGO-Hemin-BSA) nanocomposites as peroxidase mimetics was demonstrated. The developed nanocomposites of PEI-rGO-Hemin-BSA showed an excellent peroxidase-like activity. Importantly, through the glutaradelhyde crosslinking, PEI-rGO-Hemin-BSA could be further simply combined with various oxidases such as glucose oxidase, cholesterol oxidase, lactate oxidase and choline oxidase for the detection and quantitative measurement of multiple metabolites including glucose, cholesterol, l -lactate, and choline. The developed detection strategy, which is sensitive, convenient, low-costed, and in tiny sample consumption, could be expected wide applications in the disease diagnosis and management of metabolite disorders. Image 1 • PEI-rGO-Hemin-BSA nanocomposites were fabricated via π-π interactions. • The PEI-rGO-Hemin-BSA demonstrated high peroxidase-like catalytic activity. • The PEI-rGO-Hemin-BSA can combine further with an oxidase to detect its substrate. • Glucose, cholesterol, l -lactate, and choline were detected sensitively and easily. • The strategy could find an application in multiple metabolites detection. [ABSTRACT FROM AUTHOR]

Abstract This paper describes the development of two microfluidic paper-based analytical devices (μPADs), one well-based and the other based on a lateral flow assay (LFA) configuration, to detect glucose via a colorimetric assay using the solid metal-organic framework (MOF) Zr-PCN-222(Fe), to encapsulate glucose oxidase (GOx). The well-based platform consisted of laminate sheets and multiple layers of wax-printed chromatography paper. Solutions of KI and glucose placed into the well flowed through the device and reacted with the GOx@MOF species sandwiched between the paper layers realizing a yellow-brown color. The LFA platform consisted of chromatography paper between parafilm and polyvinyl acetate (PVA) layers. GOx@MOFs spotted on the paper subjected to solutions of KI and glucose yielded a brown color. The devices were then dried, scanned, and analyzed yielding a correlation between average inverse yellow intensity and glucose concentrations. The development of these devices employing MOFs as biomimetic catalysts should further expand the applications of microfluidic technologies for sensors a variety of analytes. Graphical abstract Image 1 Highlights • Paper-based microfluidic devices employing a metal-organic framework detect glucose. • Metal-organic frameworks are effective encapsulating species for enzymes. • Sensors constructed from paper are easy to fabricate and are low-cost. [ABSTRACT FROM AUTHOR]

Detecting bacterial cells at low levels is critical in public health, the food industry and first response. Current processes typically involve laborious cell lysis and genomic DNA extraction to achieve 100–1000 CFU mL −1 levels for detecting gram-positive bacteria. As an alternative to DNA-based methods, cell wall binding domains (CBDs) derived from lysins having a modular structure with an N-terminal catalytic domain and a C-terminal CBD, can be used to detect bacterial pathogens as a result of their exceptionally specific binding to target bacteria with great avidity. We have developed a highly sensitive method for multiplex detection of whole bacterial cells using self-assembled CBD complexes. Self-assembled CBD-SA-reporter complexes were generated using streptavidin (SA), biotin-CBDs, and biotinylated reporters, such as glucose oxidase (GOx) and specific DNA sequences. The simultaneous detection of three test bacteria, Staphylococcus aureus, Bacillus anthracis-Sterne, and Listeria innocua cells in PBS could be accomplished with a 96-well plate-based sandwich method using CBD-SA-GOx complex-coupled spectrophotometric assay to achieve a detection limit of >100 CFU mL −1 . To achieve greater detection sensitivity, we used CBD-SA-DNA complexes and qPCR of specific DNA barcodes selectively bound to the surface of target bacterial cells, which resulted in a detection sensitivity as low as 1–10 CFU mL −1 without cross-reactivity. This sensitive multiplex detection of bacterial pathogens using both CBD-SA-GOx and CBD-SA-DNA complexes has the potential to be quickly combined with point-of-care compatible diagnostics for the rapid detection of pathogens in test samples. [ABSTRACT FROM AUTHOR]

In this study, a cathodic photoelectrochemical (PEC) bioanalysis for sensitive determination of microRNA (miRNA) has been constructed based on CRISPR/Cas12a trans -cleavage mediated [(C6) 2 Ir(dcbpy)]+PF 6 − (C6 represents coumarin-6 and dcbpy represents 4,4′-dicarboxyl-2,2′-bipyridine)-sensitized NiO photocathode and p-n heterojunction quenching mode. The [(C6) 2 Ir(dcbpy)]+PF 6 −-sensitized NiO photocathode exhibits a stable and dramatically improved photocurrent signal due to highly effective photosensitization of [(C6) 2 Ir(dcbpy)]+ PF 6 −. Then Bi 2 S 3 quantum dots (Bi 2 S 3 QDs) is captured on the photocathode, resulting in markedly quenching of the photocurrent. When target miRNA is specifically recognized by the hairpin DNA to stimulate the trans -cleavage activity of CRISPR/Cas12a, leading to the leave of the Bi 2 S 3 QDs. The photocurrent is gradually recovered with the increasing target concentration. Thus, the quantitative signal response to target is achieved. Benefiting from excellent performance of NiO photocathode, intense quenching effect of p-n heterojunction and accurate recognition ability of CRISPR/Cas12a, the cathodic PEC biosensor shows a wider linear range over 0.1 fM–10 nM, with a low detection limit of 36 aM. Also, the biosensor exhibits satisfying stability and selectivity. [Display omitted] • Employing iridijum complex-sensitized NiO photocathode for photoelectrochemical biosensor. • Using p-n heterojunction signal quenching mode to improve detection sensitivity. • Proposing the trans -cleavage activity of CRISPR/Cas12aT to regulate signal. • Achieving a wide linear range and a low detection limit for microRNA detection. [ABSTRACT FROM AUTHOR]

The zwitterionic peptides, especially those composed of glutamic (E) and lysine (K) groups have drawn enormous attention as antifouling biomaterials owing to their strong hydration capability and biocompatibility. However, the susceptibility of α-amino acid K to the proteolytic enzymes in human serum limited the broad application of such peptides in biological media. Herein, a new multifunctional peptide with favorable stability in human serum was designed, and it was composed of three sections with immobilizing, recognizing and antifouling capabilities, respectively. The antifouling section was composed of alternating E and K amino acids, but the enzymolysis-susceptive amino acid α-K was replaced by the unnatural β-K. Compared with the conventional peptide composed of all α-amino acids, the α/β-peptide exhibited significantly enhanced stability and longer antifouling performance in human serum and blood. The electrochemical biosensor based on the α/β-peptide showed a favorable sensitivity to its target IgG, with a quite wide linear range from 100 pg mL−1 to 10 μg mL−1 and a low detection limit (33.7 pg mL−1, S/N = 3), and it was promising for the detection of IgG in complex human serum. The tactic of designing antifouling α/β-peptides offered an efficient way to develop low-fouling biosensors with robust operation in complex body fluids. A stable and low-fouling electrochemical biosensor based on designed α/β-peptide was developed for the detection of biomarker in complex human serum. [Display omitted] • A stable and low fouling electrochemical biosensor was prepared based on α/β-peptide. • α/β-peptides with anti-enzymolysis and antifouling capabilities were designed. • The α/β-peptide based biosensor was capable of assaying biomarkers in complex serum. [ABSTRACT FROM AUTHOR]

Poly(5-hydroxytryptamine) (poly(5-HT)) is exploited as a new and efficient enzyme-immobilization matrix for amperometric and biofuel cell (BFC)-based biosensing. A GOx-poly(5-HT)-Pd nanoparticles (PdNPs) bionanocomposite is prepared by Na 2 PdCl 4 -initiated oxidized polymerization of 5-hydroxytryptamine (5-HT) in a neutral aqueous solution containing glucose oxidase (GOx), and this bionanocomposite and then chitosan (CS) are cast-coated on a Pd-plated Au electrode to yield a CS/GOx-poly(5-HT)-PdNPs/Pd plate /Au enzyme electrode. Scanning/transmission electron microscopy, UV–vis spectrophotometry and electrochemical quartz crystal microbalance are employed for material characterization and/or process monitoring. Under optimized conditions, the amperometric response of the enzyme electrode is linear with glucose concentration from 2.0 μM to 6.66 mM with a sensitivity of 110 μA mM −1  cm −2 , a limit of detection of 0.2 μM, and excellent operation/storage stability in the first-generation biosensing mode. The sensitivity is larger than those of some conventional electrodes under identical conditions. The enzyme electrode also works well in the second-generation biosensing mode. By using the enzyme electrode as the anode for glucose oxidation and a Pd plate /Au electrode as the cathode for KMnO 4 reduction, a monopolar BFC is constructed as a self-powered biosensor, the current response of which is linear with glucose concentration from 50 μM to 34.5 mM. Experiments also show that poly(5-HT) is a physical and chemical dual-immobilization matrix of enzyme, since the abundant amino groups in poly(5-HT) can be used for chemical bonding of GOx. [ABSTRACT FROM AUTHOR]

For analyte detection in raw fruits, the conventional sample pretreatment method usually involves mashing (blending or homogenization), extraction, and dilution. This process is time-consuming, solvent-intensive and laborious. Usually, there is also a lot wastage with multiple fruits being combined into composite samples. In this work, a new micro-sampling approach based on a syringe needle is developed; it was coupled with micro liquid-phase extraction to determine and quantify d -glucose in bananas. This sampling and extraction approach was quick, easy and required only minimal use of solvent. The d -glucose in the extracted banana flesh was first oxidized enzymatically with glucose oxidase. The resulting peroxide was then detected colorimetrically via oxidation of 3,3′,5,5′-tetramethylbenzidine in the presence of a catalyst. The latter, consisting of an iron (III)–nickel (II) layered double hydroxide (LDH[Ni II -Fe III ]) was synthesized in this work for the purpose. The results of this new detection method for d -glucose in fruits provided low limits of detection (0.025 μg/mL), wide linear range (0.1–3000 μg/mL) and good linearity ( r 2 = 0.9998). Quantification of d -glucose using this approach was applied to banana samples over a period of 10 days. The results showed that the d -glucose levels in bananas increased as the fruits ripened, as expected. This work demonstrated a new and interesting approach for easy and efficient detection of analytes in raw fruit samples. [ABSTRACT FROM AUTHOR]

The present work deals with the development of a non-invasive optical glucose biosensor using saliva samples and a smartphone. The sensor was fabricated with a simple methodology by immobilization of Glucose oxidase enzyme along with a pH responsive dye on a filter paper based strip. The strip changes color upon reaction with glucose present in saliva and the color changes were detected using a smartphone camera through RGB profiling. This standalone biosensor showed good sensitivity and low interference while operating within 20 s response time. We used various means for improvements such as the use of slope method instead of differential response; use of a responsive pH indicator and made numerous tweaks in the smartphone app. Calibration with spiked saliva samples with slopes for (R + G + B) pixels revealed an exponentially increasing calibration curve with a linear detection range of 50–540 mg/dL, sensitivity of 0.0012 pixels sec −1 /mg dL −1 and LOD of 24.6 mg/dL. The biosensor was clinically validated on both healthy and diabetic subjects divided into several categories based on sex, age, diabetic status etc. and correlation between blood and salivary glucose has been established for better standardization of the sensor. Correlation of 0.44 was obtained between blood and salivary glucose in healthy individuals whereas it was 0.64 and 0.94 in case of prediabetic and diabetic patients respectively. The developed biosensor has the potential to be used for mass diagnosis of diabetes especially in such areas where people remain prohibited from routine analysis due to high healthcare cost. Apart from that, a smartphone would be the only device the user needs for this measurement, along with a disposable low cost test strip. [ABSTRACT FROM AUTHOR]

Fluorescence-based visual assays have sparked tremendous attention in on-site detection due to their obvious color gradient changes and high sensitivity. In this study, a novel emission wavelength shift-based visual sensing platform is constructed to detect glucose based on the oxidation of Rhodamine B (RhB). MnO 2 nanosheets (MnO 2 NS) with strong oxidizing properties were introduced to oxidize RhB, which resulted in a blue shift in the emission wavelength, and a visual color changed of the fluorescence from orange-red to green. The oxidation reaction could be inhibited via reducing and destroying MnO 2 NS by H 2 O 2 , which was produced by the oxidizing procedure of glucose in the presence of glucose oxidase (GOx). A series of wavelength shifts and fluorescence color variations appeared with the addition of various amounts of glucose. A ratiometric fluorescence glucose sensor with a lowest recorded concentration of 0.25 μM was developed. Meanwhile, test paper-based assays integrated with the smartphone platform were established for the sensing of glucose by means of the significant fluorescence color changes, offering a reliable, sensitive, and portable on-site assay of glucose. [Display omitted] • A fluorescence-based visual assays based on the oxidation of Rhodamine B was developed. • The method exhibited obvious color gradient change, and didn't require additional luminescence reference. • Smartphone combined with test paper for on-site monitoring of glucose. • Highly sensitive and selective sensing of glucose in human serum. [ABSTRACT FROM AUTHOR]

A simple tactic for electrochemical determination of a typical biomarker for breast cancer, human epidermal growth factor receptor 2 (HER2), was presented via the construction of a low fouling sensing interface functionalized with polyethylene glycol (PEG) and peptide. The HER2 biosensor was developed based on an electrode modified by the conducting polymer poly(3,4-ethylenedioxythiophene) (PEDOT) and Au nanoparticles (AuNPs) as the sensing substrate, and followed by the immobilization of an antifouling PEG and a peptide with both recognizing and antifouling properties. Thanks to the combined antifouling effect of the PEG and peptide, and the specific recognizing ability of the peptide to the target HER2, the developed electrochemical biosensor exhibited strong antifouling performances in complex biofluids, such as human blood and serum, and it was capable of assaying target HER2 within a very wide linear range (1.0 pg mL−1 to 1.0 μg mL−1), with an ultralow limit of detection (0.44 pg mL−1). The combination of two kinds of antifouling biomaterials (PEG and peptide) offered an effective strategy for the development of low fouling sensing platforms suitable for practical assay in complex biotic environments. A low-fouling electrochemical biosensor based on two kinds of antifouling materials, designed recognizing peptide and PEG was developed for the HER2 detection in complex media. [Display omitted] • An ultralow fouling biosensor for the detection of HER2 in complex biological media was developed. • The Electrochemical biosensor was constructed based on two kinds of antifouling biomaterials. • Enhanced antifouling capability was achieved through the conjugation of PEG and peptide. [ABSTRACT FROM AUTHOR]