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Stable detection of diazinon (DZN) residues in vegetables is important for food safety. In this work, an electrochemiluminescence (ECL) aptasensor with dual-catalytic glucose in-situ production of H 2 O 2 was constructed for the stable detection of DZN in vegetables. Firstly, MWCNTs@MB was prepared using π-π stacking interactions between methylene blue (MB) and multi-walled carbon nanotubes (MWCNTs) to enhance the loading of MB on an electrode and thus catalyze the generation of H 2 O 2 from glucose. Secondly, Cu 2 O@AuNPs was formed by loading AuNPs on the surface of Cu 2 O through spontaneous reduction reaction, which improved the interfacial charge transfer, Cu 2 O nano-enzyme had glucose oxidase mimicking activity and could further catalyze the production of more H 2 O 2 from glucose. MWCNTs@MB and Cu 2 O@AuNPs played a key role in the in-situ generation of co-reacting reagent H 2 O 2 , which solved the problem of unstable detection caused by the easy decomposition of the H 2 O 2 solution added to the luminescence system. In addition, the aptamer was immobilized on the electrode surface by forming Au–S bonds with Cu 2 O@AuNPs. As a result, the ECL aptasensor performed good linearity in 1.00 pg mL−1-1.00 μg mL−1 and a low limit of detection (LOD) to 0.39 pg mL−1 (S/N = 3). This work provided an effective method for the accurate and stable detection of DZN residues in vegetables, which was of great significance in ensuring food safety and assessing the environmental risk of DZN. [Display omitted] • By generating H 2 O 2 in-situ to participate in the electrochemiluminescence reaction of luminol. • This work solved the problem that additional H 2 O 2 was unstable and easy to decompose. • The synthesized MWCNTs@MB and Cu 2 O@AuNPs exerted a dual-catalytic effect on the in situ production of H 2 O 2. • The ECL aptasensor was constructed for the stable detection of diazinon in vegetables. [ABSTRACT FROM AUTHOR]

This study presents a modified screen-printed carbon electrode (SPCE) to determine glucose in a custom-built flow injection system. The biosensor was constructed by immobilizing glucose oxidase on porous platinum nanoparticles decorated on multi-walled carbon nanotubes (GOx@PPtNPs@MWCTNs). The fabrication of the biosensor was completed by coating the GOx@PPtNPs@MWCTNs nanocomposite on an SPCE modified with a nanocomposite of poly(3,4-ethylenedioxythiophene) and Prussian blue (GOx@PPtNPs@MWCTNs/PEDOT@PB/SPCE). The fabricated electrode accurately measured hydrogen peroxide (H 2 O 2), the byproduct of the GOx-catalyzed oxidation of glucose, and was then applied as a glucose biosensor. The glucose response was amperometrically determined from the PB-mediated reduction of H 2 O 2 at an applied potential of −0.10 V in a flow injection system. Under optimal conditions, the developed biosensor produced a linear range from 2.50 μM to 1.250 mM, a limit of detection of 2.50 μM, operational stability over 500 sample injections, and good selectivity. The proposed biosensor determined glucose in human plasma samples, achieving recoveries and results that agreed with the hexokinase-spectrophotometric method (P > 0.05). Combining the proposed biosensor with the custom-built sample feed, a portable potentiostat and a smartphone, enabled on-site glucose monitoring. [Display omitted] • MWCNTs were decorated with synthesized porous PtNPs for the first time. • The GOx@PPtNPs@MWCTNs and PEDOT@PB were combined in a glucose biosensor. • The modified electrode was highly electrocatalytic towards H 2 O 2. • Blood glucose was measured by smartphone-coupled flow injection amperometry. • The developed device was operationally stable for 500 injections. [ABSTRACT FROM AUTHOR]

The development of photoelectrochemical (PEC) biosensors plays a critical role in enabling timely intervention and personalized treatment for cardiac injury. Herein, a novel approach is presented for the fabrication of highly sensitive PEC biosensor employing Bi 2 O 3 /MgIn 2 S 4 heterojunction for the ultrasensitive detection of heart fatty acid binding protein (H-FABP). The Bi 2 O 3 /MgIn 2 S 4 heterojunction, synthesized through in-situ growth of MgIn 2 S 4 on Bi 2 O 3 nanoplates, offers superior attributes including a larger specific surface area and more homogeneous distribution, leading to enhanced sensing sensitivity. The well-matched valence and conduction bands of Bi 2 O 3 and MgIn 2 S 4 effectively suppress the recombination of photogenerated carriers and facilitate electron transfer, resulting in a significantly improved photocurrent signal response. And the presence of the secondary antibody marker (ZnSnO 3) introduces steric hindrance that hinders electron transfer between ascorbic acid and the photoelectrode, leading to a reduction in photocurrent signal. Additionally, the competition between the ZnSnO 3 marker and the Bi 2 O 3 /MgIn 2 S 4 heterojunction material for the excitation light source further diminishes the photocurrent signal response. After rigorous repeatability and selectivity tests, the PEC biosensor exhibited excellent performance, and the linear detection range of the biosensor was determined to be 0.05 pg/mL to 100 ng/mL with a remarkable detection limit of 0.029 pg/mL (S/N = 3). For TOC graphic only. [Display omitted] • A novel PEC biosensor formed with Bi 2 O 3 /MgIn 2 S 4 photoelectrode was first reported. • ZnSnO 3 as the signal quenching source achieves multiple signal amplification effect. • Photoelectrodes provide powerful photocurrent response. • The PEC biosensor shows broad linear range with low detection limit for H-FABP. [ABSTRACT FROM AUTHOR]

Implementing the concept of turning waste into treasure, the conversion of biomass waste into high-value carbon materials, especially carbon dots (CDs), has pointed out a new direction for disease diagnosis, tumor treatment, and other aspects. In this work, we have reported the GL-CDs(Fe) via a simple synthesis route exploiting Ganoderma lucidum waste as the precursor. Thanks to their excellent optical property and peroxidase mimetic activity, a novel GL-CDs(Fe)-based ratio fluorescence/colorimetric/smartphone triple mode sensing platform is cleverly fabricated for glucose determination with the LOD of 0.28, 0.37, and 0.52 μΜ separately. Especially, this triple mode biosensor is successfully utilized for glucose detection in serum samples with the relative error of less than ±8 % compared with clinical reports. Surprisingly, the GL-CDs(Fe) also presents immense application prospects in high-level anti-counterfeiting aspects due to their excellent luminescent properties, high water-solubility, and easy availability. Furthermore, GL-CDs(Fe) can catalyze excessive H 2 O 2 inside tumor cells to produce massive hydroxyl radicals (· OH) which break down the redox levels of cancer cells and thereby eliminate tumor cells. Thus, this integrated "Three-in-One" multifunctional platform based on GL-CDs(Fe) unveils enormous research and application prospects for bio-sensing, anti-counterfeiting, cancer treatment. [Display omitted] • GL-CDs(Fe) with ideal optical and peroxidase-like property was derived from biomass waste. • A novel GL-CDs(Fe)-based triple mode sensing platform was fabricated for glucose analysis. • GL-CDs(Fe) was also used for anti-counterfeiting ink and anticancer cell effect. [ABSTRACT FROM AUTHOR]

The rapid developments in the field of zeolitic imidazolate frameworks (ZIFs) in recent years have created unparalleled opportunities for the development of unique bioactive ZIFs for a range of biosensor applications. Integrating bioactive molecules such as DNA, aptamers, and antibodies into ZIFs to create bioactive ZIF composites has attracted great interest. Bioactive ZIF composites have been developed that combine the multiple functions of bioactive molecules with the superior chemical and physical properties of ZIFs. This review thoroughly summarizes the ZIFs as well as the novel strategies for incorporating bioactive molecules into ZIFs. They are used in many different applications, especially in biosensors. Finally, biosensor applications of bioactive ZIFs were investigated in optical (fluorescence and colorimetric) and electrochemical (amperometric, conductometric, and impedance) fields. The surface of ZIFs makes it easier to immobilize bioactive molecules like DNA, enzymes, or antibodies, which in turn enables the construction of cutting-edge, futuristic biosensors. [Display omitted] • Biosensor-based bioactive ZIFs consist of bioactive molecules like DNA, and enzymes. • The surface of ZIFs makes it easier to immobilize bioactive molecules. • Special features of bioactive ZIFs improved the sensitivity. • Bioactive ZIFs have been used in optical and electrochemical biosensors. [ABSTRACT FROM AUTHOR]

Organic photoelectrochemical transistor (OPECT) biosensor is now appearing in perspective of public, which characterized by amplified the grating electrode potential by ion transport. In this study, the DNA network formed by the hybridization chain reaction (HCR) detects the target adenosine triphosphate (ATP) by adjusting the surface potential of the new heterojunction of ZnIn 2 S 4 /MXene. The formation of DNA network amplifies the detection signal of ATP. Significantly, OPECT biosensor could further amplify the signal, which calculated the gain achieved 103, which is consistent with the gain signal of the previously reported OPECT biosensor. Furthermore, the OPECT biosensor achieved a highly sensitivity detection of the target ATP, which the linear detection range is 0.03 pM–30 nM, and the detection limit is 0.03 pM, and illustrated a high selectivity to ATP. The proposed OPECT biosensor achieved signal amplification by adjusting the surface potential of ZnIn 2 S 4 /MXene through cascade DNA network, which provides a new direction for the detection of biomolecules. We designed an ultrasensitive method for organic photoelectrochemical transistor detection of ATP based on DNA network structure modulated ZnIn 2 S 4 /MXene schottky junction. [Display omitted] • A new Schottky junction of MXene/ZnIn 2 S 4 is applied to organic phototransistors. • An enzyme-free labelled DNA-assisted isothermal amplification system was designed. • The detection of ATP with organic photoelectrochemical transistor was realized. [ABSTRACT FROM AUTHOR]

Continuous glucose monitoring is very important to daily blood glucose control in diabetic patients, but its accuracy is limited by the narrow linear range of the response of biosensor to the glucose concentration because of the oxygen starvation in tissue and the limited maximum conversion rate of glucose oxidase. In this work, a biocompatible diffusion limiting membrane based on two medical-grade polyurethanes is developed via blending modification to restrict the diffusion flux of glucose to match the oxygen concentration and the maximum conversion rate. The expansiveness of the linear range for the nanomaterials-modified electrode in the glucose biosensor can be achieved through the regulation of two polyurethanes, the solvent, and the thickness of the membrane. In addition, the mass transport of hydrogen peroxide and interfering substances is also limited of the membrane. The in vitro experiments demonstrated that the membrane-modified microneedle biosensor exhibited a rapid response to the concentration variation of glucose, a wide linear range that is sufficient to cover the blood concentration of healthy and diabetic people, the ability to resist the oxygen concentration fluctuation and interfering substances, good reproducibility and long-term stability. The custom wearable electrochemical system, possessing these characteristics, has been proven to accurately monitor the blood concentration in a living rat in real time. This demonstrates a significant potential for application in both daily and clinical blood glucose monitoring. [Display omitted] • A biocompatible membrane, derived from two polyurethanes and formulated through predissolution in a binary solvent, modified via physical blending, formed through ultrasonic spraying, proficiently regulates the diffusion of glucose to the biosensor. • The linear range can be expanded by the regulation of the hydrophilic and hydrophobic polyurethanes ratio, the solvents and the membrane thickness. • The membrane-decorated biosensor exhibited a broad linear response range, resistance to fluctuations in oxygen concentration and interference, low relative standard deviation, excellent reproducibility and long-term stability. • In vivo experiment confirms the CGM device combined with the membrane-coated glucose biosensor can monitor interstitial fluid glucose concentration in real-time accurately for 8 days. [ABSTRACT FROM AUTHOR]

The development of rapid screening sensing platforms to improve pre-screening mechanisms in community healthcare is necessary to meet the significant need for portable testing in biomarker diagnostics. Here, we designed a portable smartphone-based photoelectrochemical (PEC) immunoassay for carcinoembryonic antigen (CEA) detection using Cu-doped ultrathin porous Bi 2 WO 6 (CuBWO) nanosheets as the photoactive material. The CuBWO nanosheets exhibit a fast photocurrent response and excellent electrical transmission rate under UV light due to their surface plasmon resonance effect (SPR). The method uses glucose oxidase-labeled secondary antibody as a signal indicator for sandwich-type immune conjugation. In the presence of the target CEA, the electrons and holes generated at the surface of the photo-excited ultrathin porous CuBWO were rapidly consumed by the production of H 2 O 2 from glucose oxidase oxidizing glucose, resulting in a weakened photocurrent signal. The photocurrent intensity increased logarithmically and linearly with increasing CEA concentration (0.02–50 ng mL−1), with a detection limit of 15.0 pg mL−1 (S/N = 3). The system provides a broader idea for inferring the electron-hole transport mechanism in ultrathin porous nanosheet layer materials and developing efficient PEC sensors. [Display omitted] • SPR-enhanced Cu-doped ultra-thin porous Bi 2 WO 6 for improving sensitivity of PEC immunoassay. • SPR effect from Cu doping enhances light absorption activity and increases electron transfer efficiency. • The integrated micro-device achieves efficient conversion of biological and optoelectronic signals. • This immunoassay avoids the interference of photoexcitation and photoactive materials. [ABSTRACT FROM AUTHOR]

In this study, a self-powered biosensor based on an enzymatic biofuel cell was proposed for the first time for the ultrasensitive detection of soluble CD44 protein. The as-prepared biosensor was composed of the co-exist aptamer and glucose oxidase bioanode and bilirubin oxidase modified biocathode. Initially, the electron transfer from bioanode to biocathode was hindered due to the presence of the aptamer with high insulation, generating a low open-circuit voltage (EOCV). Once the target CD44 protein was present, it was recognized and captured by the aptamer at the bioanode, thus the interaction between the target CD44 protein and the immobilized aptamer caused the structural change at the surface of the electrode, which facilitated the transfer of electrons. The EOCV showed a good linear relationship with the logarithm of the CD44 protein concentrations in the range of 0.5–1000 ng mL−1 and the detection limit was 0.052 ng mL−1 (S/N = 3). The sensing platform showed excellent anti-interference performance and outstanding stability that maintained over 97% of original EOCV after 15 days. In addition, the relative standard deviation (1.40–1.96%) and recovery (100.23–101.31%) obtained from detecting CD44 protein in real-life blood samples without special pre-treatment indicated that the constructed biosensor had great potential for early cancer diagnosis. [Display omitted] • An EBFC-SPB was proposed firstly for the ultrasensitive CD44 protein sensing. • The CD44 protein detected by the aptamer at bioanode caused the positive response. • The wide logarithm linear relationship was in the range of 0.5–1000 ng mL−1. • The detection limit was as low as 0.052 ng mL−1 (S/N = 3). • It showed excellent anti-interference performance and recovery for real sample. [ABSTRACT FROM AUTHOR]

Diabetes is a common chronic metabolic disease. The frequent fluctuation of glucose is the main cause of most diabetes complications, which in turn causes harm to the health of patients. Surface-enhanced Raman scattering (SERS) spectroscopy has attracted much attention in the rapid detection of glucose due to its unique molecular fingerprinting ability, ultra-high sensitivity and fast response. However, due to the low affinity between glucose and SERS substrate, poor signal, susceptibility to complex environmental interference, and poor stability of SERS detection, it is still a challenge for SERS to accurately and sensitively determine glucose in complex environments. In this work, we encapsulated 4-mercaptobutyronitrile (4-MBN) as an internal standard (IS) in Au@Ag NRs inside and then Au@4-MBN@Ag NRs, Leucomalachite Green (LMG), glucose oxidase (GOx) and horseradish peroxidase (HPR) were encapsulated in ZIF-8 to prepare a tandem enzyme catalytic ratiometric SERS sensor Au@4-MBN@Ag@LMG@ZIF-8(GOx, HPR) for the detection of glucose in saliva. Because ZIF-8 enhanced the catalytic activity of the enzyme, the ability of glucose enrichment, and weakens the aggregation of Ag NRs. The internal standard signal molecule improves the accuracy and sensitivity of detection. The ratiometric Raman signal I 412 /I 2233 of glucose has a good linear relationship with the concentration in the range of 0.1–100 μM, and the limit of detection (LOD) could be down to 0.03 μM. At the same time, it has excellent selectivity, repeatability and accuracy. The recovery rate of glucose in saliva is 96.50%–105.56 %, which proves the feasibility of the method. The Au@4-MBN@Ag@LMG@ZIF-8(GOx, HPR) sensor prepared in this study showed excellent SERS performance, which was able to detect glucose quickly, sensitively and accurately. This work provides a new strategy for the design of enzyme-catalyzed SERS sensors. [Display omitted] • A novel ratiometric glucose SERS sensor was successfully prepared. • Au@4-MBN@Ag NR is individually encapsulated in ZIF-8 crystals to improve SERS signal stability. • As a stationary carrier, ZIF-8 can effectively prevent biological and chemical degradation. • Detection of ratiometric Raman improves the sensitivity and accuracy of detection. [ABSTRACT FROM AUTHOR]

In this work, we have realized the strong anodic ECL emission of Ru(bpy) 3 2+ at ionic liquid (N-butylpyridinium tetrafluoroborate) modified electrode without additional coreactant. Methylene blue (MB) could accept the energy of Ru(bpy) 3 2+ ECL to construct resonance energy transfer (ECL-RET) system, leading to the decrease of ECL signal. In the presence of glucose oxidase, hydrogen peroxide generated from the oxidation process of glucose could oxidize MB and block the ECL-RET route, resulting in the recovery of ECL signal. As a consequence, the designed sensor showed outstanding performance for "signal-on" detection of glucose in the concentration range of 10 μM to 1 mM, and the detection limit was determined as 1.75 μM. Importantly, this study revealed new roles of ILs in the fabrication of coreactant-free ECL sensing, which might open up a promising route for the potential design and implement in clinical analysis. Strong anodic Ru(bpy) 3 2+ ECL was obtained at ionic liquid modified electrode without coreactant. ECL resonance energy transfer between Ru(bpy) 3 2+ ECL and methylene blue could inhibit ECL signal. Hydrogen peroxide generated from glucose could oxidize methylene and block the energy transfer route, resulting in the recovery of ECL signal. As a result, an "off-on" mode ECL sensor for sensitive and selective detection of glucose was proposed. [Display omitted] • Coreactant-free Ru(bpy) 3 2+ ECL was obtained at ionic liquid modified electrode. • ECL-RET could occur between Ru(bpy) 3 2+ ECL and methylene blue. • The oxidation of methylene blue could block the ECL-RET process. • An ECL sensor was fabricated to sensitively detect glucose. [ABSTRACT FROM AUTHOR]

Enzymatic electrochemical biosensor is the most common analytical platform for medical diagnosis. To mimic the biological environment of the enzyme for maintaining the function of biosensor, zwitterionic hydrogels have been recognized as effective matrices for enzymatic immobilization. Herein, a zwitterionic hydrogel derived from a copolymer, poly[2-methacryloyloxyethyl phosphorylcholine (MPC)- co - N -methacryloyloxyethyl tyrosine methylester (MAT)] (PMM) was firstly applied as versatile coating to preserve stability and activity of oxidase enzymes, glucose oxidase (GOx) and lactate oxidase (LOx) for enzymatic electrochemical sensor. A screen-printed carbon electrode (SPCE) was sequentially coated with nitrogen-doped graphene (NDG), oxidase enzyme, and PMM mixed with Ru(II)bpy 3 2+ and (NH 4) 2 S 2 O 8 followed by visible light irradiation for 3 min to induce PMM gelation. Electrochemical detection of glucose and lactate using the modified SPCE was performed via amperometry in the presence of hydrogen peroxide. The activity of both GOx and LOx immobilized on the modified SPCE was well maintained for 49 days at 87 and 80 %, respectively. Additionally, two different electrodes, a screen-printed graphene electrode (SPGE), and a screen-printed silver electrode (SPAgE), similarly modified gave the same satisfactory detection of spiked glucose and lactate in human plasma and sweat with 93–118 % recovery. This indicates the potential of the PMM hydrogel as a universal platform for preservation of enzymes which can be easily fabricated without the need for specific chemical modification of the electrode. [Display omitted] • Zwitterionic hydrogel was formed via visible light-induced crosslinking. • SPCE was modified by sequential coating of NDG, enzyme and PMM hydrogel. • Electrochemical detection has acceptable recovery in human plasma and sweat. • Activity of oxidase enzyme can be maintained for at least 80 % for up to 49 days. • PMM hydrogel can be applied as a universal coating for enzyme-based sensors. [ABSTRACT FROM AUTHOR]

We report on the drop-cast production of glucose biosensors based on the most efficient bioelectrocatalysis by pyrroloquinoline quinone dependent glucose dehydrogenase (PQQ GDH). To orient the enzyme upon immobilization we suggest using poly(Methylene Green) (p(MG)) nanoparticles acting as anchors. Synthesis of polymeric anchors has been carried out in course of Methylene Green electropolymerization, which allowed to tune polymer-to-monomer ratio in the drop-cast mixtures varying the monomer concentration and applying different number of potential sweep cycles. Except for elimination of electrochemical step for the electrode modification, opening the prospects for mass-production, the use of drop-cast enzyme anchors provides advantageous characteristics of the resulting biosensors. Catalytic current of PQQ GDH immobilized over p(MG) nanoparticles obtained in optimal conditions is increased only 2–2.5 times after addition of the freely diffusing mediator. Obviously, the lowest ratio of mediated-to-reagentless current points to the most efficient bioelectrocatalysis. The obtained ratio is 2.5 times lower than that for biosensors based on electropolymerized p(MG) films and practically an order of magnitude lower than that for the best reagentless sensors based on PQQ GDH immobilized over conductive nanomaterials. The achieved most efficient bioelectrocatalysis provides high sensitivity of the elaborated biosensors even at 0.0 V potential, which allows to operate them in power generation mode and control relative sweat glucose variation as a tool for non-invasive diabetes monitoring. [Display omitted] • Drop-cast polyazine anchors for PQQ glucose dehydrogenase were elaborated • The most efficient bioelectrocatalysis by PQQ glucose dehydrogenase was achieved • Power-generating biosensors are applicable for diabetes control by sweat analysis [ABSTRACT FROM AUTHOR]

The demand for sensitive, portable, and non-destructive analysis of pathogenic bacteria is of significance in point-of-care diagnosis. Herein, we constructed a smart electrochemiluminescence (ECL) biosensor by integrating a flexible paper-based sensing device and a disposable three-electrode detecting system. Staphylococcus aureus (S. aureus)-responsive cellulose paper was prepared by employing aptamer as recognition element and a probe DNA (probe DNA-GOD) tagged with glucose oxidase (GOD) as a signal amplification unit. The formation of aptamer- S. aureus complex mediated the quantitative release of probe DNA-GOD. The remaining probe DNA-GOD on the paper-based aptasensor was then activated by glucose, which resulted in a significant decrease in ECL signal. To further improve the ECL performance of biosensor, a large number of Ru(bpy) 3 2+ molecules were embedded into porous zinc-based metal-organic frameworks (MOFs) to form Ru(bpy) 3 2+ functionalized MOF nanoflowers (Ru-MOF-5 NFs). Such biosensor enabled accurate, non-destructive, and real-time monitoring of S. aureus -contaminated food samples, opening a new avenue for sensitive recognition of pathogenic bacteria. [Display omitted] • A wearable, disposable and smart paper-based biosensor was developed. • The sensor realized the sensitive, in situ and non-destructive analysis of S. aureus. • The limit of detection from our sensor was better than that of some existing methods. • The practical application in the field of S. aureus -contaminated foods was feasible. [ABSTRACT FROM AUTHOR]

Superhydrophobic gold film embedded PDMS was employed as a novel platform for digital magnetofluidics. The device performance for lab-on-a-chip applications was investigated by demonstrating four types of reactions. First, acid-based titration was introduced as a simple mixing reaction. Second, colorimetric detection of phosphate based on the molybdenum blue method was represented as a more complicated reaction. The fabricated device was able to determine the amount of phosphate in the concentration range of 10–100 ppm with %RSD of color intensity of less than 5%. Third, colorimetric detection of glucose using glucose oxidase was demonstrated as an enzymatic reaction. A linear range of 1–20 mM for determination of glucose was applied for measuring glucose in beverages with recovery percentages of glucose in the acceptable range of 89.6–106.8%. Finally, multistep analysis of C-reactive protein (CRP) based on immunomagnetic separation was successfully demonstrated on this proposed device. Therefore, the superhydrophobic gold-coated PDMS has shown its ability to be a simple platform for digital magnetofluidics for a variety of applications in the field of lab-on-a-chip technology. [Display omitted] • Superhydrophobic PDMS was employed as a novel platform for digital magnetofluidics. • Four types of lab-on-a-chip reactions were demonstrated on the fabricated device. • The proposed device is highly suitable for multi-step lab-on-a-chip applications. [ABSTRACT FROM AUTHOR]

The establishment of sensitive and facile colorimetric platform based on the CRISPR (clustered regularly interspaced short palindromic repeats)-Cas (CRISPR-associated) system is of great significance for in vitro diagnosis. Herein, we develop a dual-enzyme cascade amplification strategy based on CRISPR-Cas12a and glucose oxidase (GOx) for instrument-free and sensitive detection of target analytes. HPV-16 DNA as the model nucleic acid target directly initiated CRISPR-Cas12a-based signal transduction, resulting in the enzymatic cleavage of ssDNA linker and the release of GOx from magnetic nanoparticles 1 (MNPs1). Following simple magnetic separation, the supernatant containing GOx was taken out and used to catalyze the substrate, resulting in a visually detectable color change. The detection limit (LOD) of HPV-16 DNA was as low as 1 pM, and the entire process could be completed within 70 min without the need for expensive equipment. Notably, the dual-enzyme cascade amplification strategy was successfully applied to the detection of non-nucleic acid targets, such as ATP, via a simple signal transduction process. The visual LOD for ATP detection reaches 2.5 μM. The approach provides a robust, sensitive and reliable point-of-care biosensing platform for the detection of target analytes. [Display omitted] • CRISPR-Cas12a-based dual-enzyme cascade amplification strategy has been designed. • HPV-16 and ATP can be visually analyzed with satisfactory detection performance. • The operation procedure is simple without expensive instruments. [ABSTRACT FROM AUTHOR]

Herein, the hollow Prussian blue with ultra-small silver nanoparticle agents (Ag-HPB) was prepared by the coating-etching method by applying Prussian blue (PB) coating on Ag nanoparticles (Ag NPs) and diffusing Ag NPs into the PB framework. The flexible biosensing platform based on Ag-HPB nanocomposites incorporated the excellent electrical conductivity of Ag NPs and the superior enzyme loading capacity of the hollow structure, which significantly enhanced its sensing performance. Subsequently, take glucose oxidase (GOx) and acetylcholinesterase (AChE) as examples. The sensing platform displayed a good sensitive response to glucose (Glu) (24.37 μA mM−1 cm−2) and a considerable limit of detection (LOD) for trichlorfon (TCF) as 2.28 pg/mL while exhibiting high stability and good reproducibility. Moreover, it can be applied to monitor trichlorfon in apple samples. Promisingly, the Ag-HPB prepared by the coating-etching strategy provides a reliable strategy for further development of sensitive and flexible biosensing platforms with excellent electrical conductivity and high enzyme loading. Fig. 1. Schematic diagram of integration of flexible biosensor platform based on Ag-HPB and detection performance of various substrates.In this work, hollow Prussian Blue with ultra-small silver nanoparticle (Ag-HPB) hybridization with the high specific surface area, low density and abundant internal voids of the hollow structure was prepared by coating etching, which showed a good electrical conductivity and stronger enzyme loading capacity. Meanwhile, the electrochemical rate constants of Ag-HPB are significantly higher than pure PB through synergistic interactions. Subsequently, a flexible biosensing platform based on Ag-HPB nanocomposites was prepared using screen printing technology (Fig. 1). Afterwards, glucose oxidase (GOD) and acetylcholinesterase (AChE) were used as examples to verify sensing performance of the flexible platform. Promisingly, this work provides a reliable strategy for the further development of sensitive and flexible biosensing platforms with excellent conductivity and high enzyme loading. [Display omitted] • Hollow Prussian blue hybridized with silver nanoparticles was synthesized by coating etching with high electrical conductivity and strong loading properties. • A highly sensitive and strongly loaded flexible sensing platform was integrated by one-step method. • The flexible biosensing platform shows attractive detection performance of glucose (sensitivity = 24.37 μA mM−1 cm−2) and organophosphorus pesticides (LOD = 2.28 ppt). [ABSTRACT FROM AUTHOR]

The detection of miRNA in cells is difficult owing to its substantially low cellular content. Therefore, developing a highly sensitive sensor to detect cellular miRNA remains a significant challenge. Herein, we report an enzyme-assisted biosensor with target cycle amplification that can trigger the unlocking of locked hairpin probes for sensitive and robust let-7a gene detection. In the research, three kinds of hairpin probes were skillfully designed. The hairpin probe comprises a complementary sequence of a target, primer, and recognition site of Nt. Bbv CI restriction endonucleases. In addition, the alternating synergistic impact of polymerase and the nicking enzyme generates considerable triggers to unlock the locked hairpin probe LH1, consequently triggering a subsequent circulating strand displacement reaction to form a stable H1–H2 double strand to ensure sufficient distance between a fluorophore on H1 and a quenching group on bolt DNA (bDNA), and resulting in the recovery of fluorescence. Furthermore, this process does not require complicated operation procedures and instruments, and the target gene let-7a can be sensitively detected. Specifically, the detection limit of the biosensor is as low as 160 fM, and its linear range is 0.5 pM–250 nM. Moreover, this biosensor can be employed to detect let-7a in human serum with good selectivity. [Display omitted] • An enzyme-assisted fluorescent sensing system was proposed for the detection of the miRNA Let-7a. • The sensitivity of miRNA Let-7a fluorescence detection was further enhanced by target cyclic amplification. • Ultrasensitive enzyme-assisted fluorescent detection limit of Let-7a was estimated to be as low as 160 fM. • The biosensor has good specificity and excellent detection capabilities in a complex substrate environment. [ABSTRACT FROM AUTHOR]

In this work, we present a smartphone-based multiplexed enzymatic biosensor utilizing the unique colorimetric properties of the poly(aniline- co -anthranilic acid) (ANI- co -AA) composite film coupled with horseradish peroxidase (HRP), glucose oxidase (GOx), horseradish peroxidase-glucose oxidase (GOx-HRP) and tyrosinase (Tyr) enzymes. The enzymes are immobilized on the composite polymer film by adsorption and they catalyze a reversible redox color change of the host polymer from green to blue in the presence of their substrate. A smartphone was applied as color detector, for image acquisition and data handling. A ColorLab® android application, free of charge software application, was used to enable easy and clear display of the sensors' response indicating remarkable changes in the optical features. The results were confirmed by the spectrophotometric measurements. The developed colorimetric enzymatic biosensors were studied and optimized in relation to different experimental parameters. Moreover, the colorimetric enzymatic biosensors were applied to food and pharmaceutical analysis. It has been shown by these studies that the colorimetric biosensors are promising as quick and simple tests for handheld analysis in various fields. Image 1 • Colorimetric enzymatic assay based on poly(aniline- co -anthranilic acid) composite film is developed. • Smartphone-based visual enzymatic assay for screening applications. • A colorimetric multi enzymatic assay for hydrogen peroxide, glucose and catechol detections. • Application to spiked food and pharmaceutical samples was successfully performed. [ABSTRACT FROM AUTHOR]

The paper describes the development of an amperometric biosensor using Prussian Blue (PB) modified electrodes containing xanthine oxidase (XOD). The enzyme is immobilized by photo-polymerization into an azide-unit pendant water-soluble photopolymer (PVA-AWP). The parameters of the fabrication of the biosensor, XOD:PVA/AWP ratio, crosslinking irradiation time, and XOD charge, were optimized. Operational conditions for electrode preparation were defined as 1:2 ratio of XOD:PVA/AWP; exposure time to neon light of 30 min; pH = 7.5 at room temperature and enzymatic charge of 8 mU per electrode. The biosensors showed stable, fast, simple, selective, cost-effective and sensitive (-2.72E-8 A mol L-1), with a good linear range (1.0–75 μmol L-1), and respectively detection and quantification limits for antioxidants of 2.17, and 7.15 μmol L-1. The applicability of this biosensor was demonstrated by in vitro analysis of gallic acid as standard antioxidant and Amazonian fruits as natural sources. Image 1 • A highly sensitive biossensor for antioxidant capacity determination was developed. • The optimization of the biofunctionalization conditions were defined by chemometric modelling. • The developed biosensor exhibits good stability, sensitivity, cost-effective and limit of detection. • Practical applications were demonstrated by analyzing fruit samples. [ABSTRACT FROM AUTHOR]

A disposable microfluidic electrochemical paper-based device for multiplexed analysis based on sixteen independent microfluidic channels with electrochemical detection is proposed. A major advantage of this work was the non-necessary use of a wax printer for devices manufacturing which has a high cost of operation. In addition, a commercial multiplexing module was used that has the multiplexing capability of 8–16 channels and, for the first time using this module, the strategy of multiplexing both the working and reference electrodes were used. These sixteen channels with the respective sensors can be operated employing one or multiple electrochemical techniques with good repeatability and reproducibility for high throughput analysis. As a proof of concept, the electrochemical performance of device was tested with ferrocenecarboxylic acid solution employing cyclic voltammetry, square-wave voltammetry, differential-pulse voltammetry and chronoamperometry. This innovative sensing platform presented capacity of production in large scale and application for clinical tests with safety and short time of assays. A biosensor was constructed using glucose oxidase on the platform for the glucose determination in urine as a non-invasive strategy. The analytical curve was linear in the glucose concentration range from 1.0 × 10−4 mol L−1 to 4 × 10−2 mol L−1, with a limit of detection of 3 × 10−5 mol L−1. Image 1 • The disposable low-cost microfluidic device proposed allows the high-throughput multiplexed analysis using a small sample volume of 60 μL. • Analytes of interest for clinical analysis can be detected with 16 independent microfluidic channels in multiplexed analysis. • Themicrofluidic device was successfully applied for the determination of glucose in non-invasive samples of urine. [ABSTRACT FROM AUTHOR]

The present work reports the preparation of advanced functional nanostructures based on cobalt oxide supported mesoporous carbon framework (Co 3 O 4 @MCF) for electrochemical biosensing. Co 3 O 4 @MCF was synthesized by simple hythrothermal & pyrolysis method and further characterized by various microscopic and spectroscopic techniques. The transmission electron microscopic (TEM) images show the lattice fringes of crystalline Co 3 O 4 with interlayer spacing of 0.24 nm. The characteristic 311 plane in X-ray diffraction (XRD) studies further confirmed the presence of crystalline Co 3 O 4 on carbon frameworks. Reflection of prominent A1g peak along with D and G band in raman spectra confirmed the successful fabrication of Co 3 O 4 @MCF nanocomposite. Prepared Co 3 O 4 @MCF manifested great porosity, good biocompatibility and large surface area which allowed effective immobilization of glucose oxidase (GOx) onto its surface using chitosan (Chi) as a binder. Thus, a nanocomposite (Co 3 O 4 @MCF-Chi-GOx) modified glassy carbon electrode (GCE) was fabricated for highly selective detection of glucose using amperometry and cyclic voltammetry. The Co 3 O 4 @MCF-Chi-GOx/GCE electrode exhibited excellent biosensing performance for glucose monitoring with detection limit of (LOD) of 107.70 μM and reproducibility of 4.7% RSD. Moreover, the biosensor holds great promise for its effective implications in point-of-care diagnostics of small biomolecules. Advanced functional nanostructure based on cobalt oxide supported mesoporous carbon framework (Co 3 O 4 @MCF) has been synthesized and successfully applied for bioelectrochemical sensing of glucose. Image 1 • Simple synthesis of Co 3 O 4 nanoparticles integrated mesoporous carbon framework (Co 3 O 4 @MCF). • Enzymatic biosensing interface was fabricated by immobilizing glucose oxidase (GOx) at Co 3 O 4 @MCF matrix. • Glucose was used as model target to exploit the electrochemical performance of Co 3 O 4 @MCF-Chi-GOx biosensing interface. • Developed biosensor exhibited high sensitivity and selectivity for glucose than dopamine, ascorbic acid and uric acid.. [ABSTRACT FROM AUTHOR]

Lanthanide coordination polymers (LnCPs) can be used as a host platform to encapsulate functional guest molecules for the construction of integrated sensing platforms. In this work, two guest molecules, rhodamine B (RhB) and glucose oxidase (GOx), were successfully encapsulated in a heterobinuclear lanthanide coordination polymer synthesized by self-assembly of Ce3+, Tb3+ and adenosine monophosphate (AMP) to form RhB&GOx@AMP-Tb/Ce. Both guest molecules show good storage stability and minimal leakage. The higher catalytic activity and stability of RhB&GOx@AMP-Tb/Ce is obtained due to the confinement effect compared to free GOx. RhB&GOx@AMP-Tb/Ce exhibits superior luminescence based on the internal tandem energy transfer process of the nanoparticles (Ce3+→Tb3+→RhB). Glucose can be oxidized in the presence of GOx to form gluconic acid and H 2 O 2. Subsequently, Ce3+ in the AMP-Tb/Ce host structure can be oxidized by H 2 O 2 to Ce4+, thereby interrupt the internal energy transfer process and cause ratiometric luminescence response. Benefiting from the synergistic effect, the smart integrated luminescent glucose probe exhibits a wide linear range (0.4–80 μM) and a low detection limit (74.3 nM) with high sensitivity, selectivity and simplicity, enabling the quantitative detection of glucose in human serum. This work describes a good strategy to construct an integrated luminescence sensor based on lanthanide coordination polymers. [Display omitted] • Integrated luminescence nanoprobe was constructed based on guest-encapsulated LnCPs. • Guest molecule exhibited high stability due to confinement effect of LnCPs. • The nanoprobe exhibited ratiometric luminescence response toward glucose. • Integrated sensing platform enabled the accurate determination of glucose in serum. [ABSTRACT FROM AUTHOR]

α-Glucosidase inhibitors (AGIs) are oral antidiabetic drugs used in the treatment of type Ⅱ diabetes. It is integral to establish methods for AGIs screening. For the detection of α-glucosidase (α-Glu) activity and screening of AGIs, a chemiluminescence (CL) platform was established based on cascade enzymatic reactions. Firstly, the catalytic activity of a two-dimensional (2D) metal-organic framework (MOF) with iron as central metal atoms and 1,3,5-benzene tricarboxylic acid as a ligand (denoted as 2D Fe-BTC) in the luminol-hydrogen peroxide (H 2 O 2) CL reaction were studied. Mechanism studies showed that the Fe-BTC may react with H 2 O 2 to produce ·OH and act as catalase to facilitate the decomposition of H 2 O 2 to produce O 2 , thus showing good catalytic activity in the luminol-H 2 O 2 CL reaction. The proposed luminol–H 2 O 2 –Fe-BTC CL system exhibited an outstanding response to glucose with the aid of glucose oxidase (GOx). The luminol-GOx-Fe-BTC system showed a detection linear range from 50 nM to 10 μM with a detection limit (LOD) of 3.62 nM for glucose detection. Then, the luminol–H 2 O 2 –Fe-BTC CL system was applied to the detection of α-glucosidase (α-Glu) activity and screening of AGIs based on cascade enzymatic reactions using acarbose and voglibose as model drugs. The IC 50 of acarbose and voglibose was 7.39 μM and 1.89 mM, respectively. [Display omitted] • 2D Fe-BTC exhibits good catalytic activity in the luminol-H 2 O 2 CL reaction. • The CL reaction has good sensitivity for glucose (3.62 nM) and α-glucosidase (0.0074 U mL−1). • A CL platform for the screening of α-glucosidase inhibitors was established. • The IC 50 of acarbose and voglibose was 7.39 μM and 1.89 mM. [ABSTRACT FROM AUTHOR]

In this paper, we describe a novel carbon dot (CD) synthesized from citric acid and tyramine using a one-step microwave heating route. Under UV irradiation, the CD displayed blue emission that was quenched in the presence of H 2 O 2 and peroxidase. This property was used to quantify glucose in biological samples, using a standard additions procedure employing a paper platform and the H 2 O 2 formed in the enzymatic reaction with glucose oxidase. The attractive features of the paper platform include low cost, easy availability, biocompatibility, and hydrophilicity. The standard additions calibration method has the advantages that it can be performed using a single device, eliminates the need for external calibration, and reduces matrix effects associated with the sample and/or non-uniformity of the paper. The method developed was applied in the analysis of certified serum and urine samples. There were no statistically significant differences between the certified concentrations and the results obtained using the paper device with standard additions (Student's t-test at 95% confidence level). Image 1 • Green synthesis of carbon dots from citric acid and tyramine. • Carbon dots were prepared by a simple, fast, one-step microwave heating method. • Domestic microwave used to synthesize carbon dots. • Glucose determination using standard addition calibration method. • A simple, low-cost, portable, and eco-friendly paper platform method was developed. [ABSTRACT FROM AUTHOR]

We report results of the studies relating to the fabrication of a surface plasmon resonance (SPR) based label-free immunosensor for real-time monitoring of endothelin-1 (ET-1), a colon cancer biomarker. A gold disk modified with a self-assembled monolayer (SAM) of 11-mercaptoundecanoic acid (11-MUA) was functionalised via covalent immobilization of monoclonal anti-ET-1 antibodies using EDC-NHS (1-(3-(dimethylamine)-propyl)-3-ethylcarbodiimide hydrochloride, N -hydroxy succinimide) chemistry. This immunosensing platform (ethanolamine/anti-ET-1/11-MUA/Au) was characterized via atomic force microscopy (AFM), contact angle (CA) and Fourier transform infrared (FT-IR) spectroscopic techniques. The fabricated SPR electrode was further used to detect ET-1 in the broad concentration range 2–100 pg mL−1, with a detection limit of 0.30 pg mL−1 and remarkable sensitivity of 2.18 mo pg−1mL. The adsorption mechanism was studied using monophasic model and the values of association (k a) and dissociation (k d) constants for anti-ET-1 and ET-1 binding were calculated to be 4.4 ± 0.4 × 105 M−1 s−1 and 2.04 ± 0.0003 × 10−3 s−1, respectively. The results obtained via analysis of serum samples of colorectal cancer patients were found to be in good agreement with those obtained from enzyme-linked immunosorbent assay (ELISA) technique. Further, electrochemical studies were performed to prove the efficacy of the fabricated platform as a point of care device for the detection of ET-1. Image 1 • Development of SPR based biosensor using a novel biomarker Endothelin-1 for CRC detection. • This SPR based sensor is label free, rapid and simple with respect to the conventional techniques for CRC detection. • The fabricated biosensor exhibits a remarkable lower detection limit of 0.30 pg mL−1. • This optical biosensor exhibits high sensitivity of 2.18 mo pg−1 mL in the linear range (2–100 pg mL−1). [ABSTRACT FROM AUTHOR]

Microfluidic paper-based analytical devices (μPADs) for detection of hydrogen peroxide and glucose have been developed. The analytical performance of colorimetric detection using the conventional starch-iodine color reaction has been significantly improved by using gelatin as the surface modifier which retains the enzyme activity in the dry filter paper strip, improves antioxidability, as well as decreases the strong background signal. Under optimal conditions, the color intensities show a good linear relationship with glucose concentration ranging from 0.5 to 5 mM and hydrogen peroxide concentration from 0.5 to 6 mM, with the detection limit of 0.05 mM and 0.1 mM, respectively. In addition, the accuracy of colorimetric sensor has been successfully assessed in detecting glucose from real human serum samples and recovery value ranges from 95.7% to 97%, which are approaching to the glucose oxidase endpoint. The new colorimetric assay exhibits high sensitivity, good selectivity, acceptable stability and reproducibility. The present approach is promising for monitoring glucose for point of care diagnostic applications, especially in regions with resource-limited settings. Image 1 • A facile and sensitive colorimetric assay was proposed based on μPADs coupled with starch-iodide-gelatin system. • The gelatin can provide biocompatible microenvironment and improve the analytical performance of colorimetric methods. • The accuracy of colorimetric sensor was successfully assessed to detect the glucose in the real serum samples. • This colorimetric assay is used to monitor glucose for point of care diagnostic applications. [ABSTRACT FROM AUTHOR]

In our work, aptamers and hemin/G-quadruplex DNAzyme modified sandwich-rod graphene quantum dots @ graphene oxide @ carbon fiber composite (DNAzyme/L-Apt/GQDs@GO@CF) was successfully prepared for sensitive and selective chemiluminescence (CL) detection of lysozyme (LZM). Initially, GQDs@GO@CF was successfully prepared and characterized. Lysozyme aptamers (L-Apt) as a recognition element and hemin/G-quadruplex DNAzyme (DNAzyme) as a catalyst of luminal - H 2 O 2 were modified on the surface of GQDs@GO@CF, sequentially. The immobilization properties of GQDs@GO@CF to L-Apt and the adsorption properties of L-Apt/GQDs@GO@CF to DNAzyme were also researched, respectively. Then, the modified sandwich-rod carbon fiber composite was applied to the construction of CL biosensor for LZM detection. When LZM existed, DNAzyme would be released from the surface of L-Apt/GQDs@GO@CF and catalyzed the reaction of luminal - H 2 O 2. Under optimized conditions, the CL biosensor for LZM detection showed wide linear range of 2.64 × 10−10 to 6.6 × 10−8 g/L and low detection limit of 1.25 × 10–11 g/L (3δ). Finally, the CL biosensor was successfully used for LZM detection in human urine samples and illustrated the potential application in pratical samples. fx1 • Sandwich-rod carbon fiber composite was successfully prepared. • Aptamers was applied to the CL biosensor as a recognition element. • The CL biosensor showed low detection limit of 1.25 × 10–11 g/L. • The CL biosensor was successfully used for urine samples. [ABSTRACT FROM AUTHOR]

Abstract Rapid and sensitive detection of live bacteria is crucial in the realm of clinical diagnosis, food industry and environmental quality control. A portable, feasible and cost-effective platform which enables rapid and accurate live bacteria detection is still challenging. Herein, we present a Bacterial Inhibition of GOX-catalyzed Reaction (BIGR) method for rapid and broad-spectrum detection of live bacteria, which results in a visible color change without any complex instrumentations. We validated this strategy with five common clinical bacteria, namely Escherichia coli, Staphylococcus aureus, Enterococcus faecalis, Streptococcus mutans and Salmonella pullorum. This method precludes the interference of dead bacteria. Only several microliters of samples and reagents are required in this assay and the overall analysis time is less than 20 min. In a further demonstration, the presented method is successfully applied for detection of ascites samples from infected mice. Our results suggest that this method serves as a rapid and dose-dependent visual detection of pathogens in the clinical and daily life. Graphical abstract fx1 Highlights • A paper-based colorimetric assay is designed for rapid detection of live bacteria at 104 CFU/mL within 20 min. • This method only needs 3 microliters of samples for analysis. • No costly instrument or any complicated nanomaterial synthesis is required. • The successful detection of bacteria in mice ascites indicates the promising potential in clinical diagnosis. [ABSTRACT FROM AUTHOR]

Abstract Acetate ion was widely used in pH buffer to control pH environment. Here we firstly found that acetate ion had mimic peroxidase activity. Acetate ions are capable of catalyzing the decomposition of hydrogen peroxide and play a similar role to that of horseradish peroxidase (HRP). Acetate catalyzes the oxidation of tetramethylbenzidine (TMB) by H 2 O 2 , which is the product of the reaction of glucose and glucose oxidase. A colorimetric sensor for H 2 O 2 and glucose was developed using acetate ions. The linear regression equation for H 2 O 2 was A = 0.0029 C + 0.0530 (C (μmolL−1), R = 0.9978), and the detection limit was 3.0 μmolL−1, whereas that for glucose was A = 0.0021 C + 0.0709 (C (μmol L−1), R = 0.9977), and the detection limit was 4.0 μmol L−1. Moreover, the proposed method was successfully applied for the detection of H 2 O 2 in human urine and glucose in human serum; thus, the proposed method could be used for the diagnosis of illness or disease. A single-enzyme-based glucose test paper was firstly prepared and tested for semi-quantitative analysis of glucose. Graphical abstract fx1 Highlights • The authors firstly discovered the peroxidase-mimicking activity of acetate ion. • Acetate ion was applied to develop colorimetric sensor for H 2 O 2 and glucose based upon its catalysis oxidation of TMB. • Single-enzyme based test paper for glucose was firstly prepared according to the novel characteristics of acetate ions. [ABSTRACT FROM AUTHOR]

Abstract In order to realize the multi-analyte assays for physiological molecules and environmental contaminants, a bi-enzyme biosensor based on horseradish peroxidase (HRP)-catalyzed noradrenalin (NA) polymerization in the presence of H 2 O 2 was fabricated for the first time and utilized in immobilizing HRP and glucose oxidase (GOx) simultaneously. The resultant bi-enzyme modified electrode was demonstrated to be efficient in monitoring multi-analyte (H 2 O 2 , Cr(III), glucose, and Cr(VI)). It was shown that the prepared PNA-HRP-GOx/Pt electrode exhibits a sensitivity (S) high up to 628.4 μA mM−1 cm−2 in the linear range (LR) of 0.50 μM ~ 0.42 mM and a S of 208.9 μA mM−1 cm−2 in the LR of 0.42 mM~3.5 mM in glucose sensing, with a limit of detection (LOD) of 0.08 μM observed; in Cr(VI) sensing a LOD of 0.20 nM and a LR of 0.50 ~ 6.0 nM were obtained. With the addition of polyaniline (PANI), the resultant PNA-HRP-GOx/PANI/Pt electrode potentiostated at − 0.20 V responded linearly to H 2 O 2 concentration in 0.05 ~ 30.2 mM range, with linearly responses to Cr(III) concentration in the LR of 0.01 ~ 3.8 μM. Hence, amperometric biosensors with high S , low LOD and good anti-interference ability for detection of glucose, H 2 O 2 and heavy metal ions (Cr(III) and Cr(VI)) were developed. Graphical abstract fx1 Highlights • Immobilization of bi-enzyme via HRP-catalyzed polymerization of noradrenalin. • The thus-prepared HRP and GOx immobilized electrodes exhibit excellent performance. • The proposed biosensors realized the ultrasensitive biosensing of multi-analytes. [ABSTRACT FROM AUTHOR]

Determining glucose in biological samples is tedious and time-consuming due to sample pretreatment. The sample is usually pretreated to remove lipids, proteins, hemocytes and other sugars that interfere with glucose detection. A surface-enhanced Raman scattering (SERS) active substrate based on hydrogel microspheres has been developed to detect glucose in biological samples. Due to the specific catalytic action of glucose oxidase (GOX), the high selectivity of detection is guaranteed. The hydrogel substrate prepared by microfluidic droplets technology protects the silver nanoparticles from the surrounding environment and improves the stability and reproducibility of the assay. In addition, the hydrogel microspheres have size-adjustable pores that selectively allow small molecules to pass through. The pores block the entry of large molecules, such as impurities, enabling glucose detection through glucose oxidase etching without sample pretreatment. This hydrogel microsphere-SERS platform is highly sensitive and enables reproducible detection of different glucose concentrations in biological samples. The use of SERS to detect glucose provides clinicians with new diagnostic methods for diabetes and a new application opportunity for SERS-based molecular detection techniques. Overview of a workflow of the SERS active substrate based on hydrogel microspheres for pretreatment-free detection of glucose in biological samples. [Display omitted] • A pretreatment-free method for detection of glucose in blood and urine. • The specificity of glucose oxidase determines the high selectivity of the method. • Repeatability & stability due to nanoparticles' uniform distribution in microspheres. • Requiring a small volume of samples. • The method has a fast response time and high sensitivity. [ABSTRACT FROM AUTHOR]

Protein kinase A (PKA) can regulate many cellular biological processes by phosphorylation substrate peptide or protein. Sensitive detection of PKA activity is critical for the PKA-related drug discovery and disease diagnosis. A new electrochemical biosensing method was developed for detection of PKA activity based on Zr4+-mediated DNAzyme-driven DNA walker signal amplification strategy. In this strategy, the special designed substrate peptide and a thiolated methylene blue-labeled hairpin DNA (MB-hpDNA) containing a single ribonucleic acid group (rA) could be anchored on the surface of gold electrode by Au–S bond. In the presence of adenosine triphosphate (ATP) and PKA, substrate peptide was phosphorylated and linked with walker DNA (WD) via the robust phosphate-Zr4+-phosphate chemistry. The linked WD hybridized with the loop region of MB-hpDNA to form a Mn2+-dependent deoxynuclease (DNAzyme), which cleaved the MB-hpDNA into MB-labeled fragment releasing away from electrode surface, resulting in a dramatic decrease of electrochemical signal and providing an electrochemical sensing platform for PKA activity detection. The response signal of the developed biosensor is proportional to the logarithm of PKA concentration in the range of 0.05 U mL−1 to 100 U mL−1, with a detection limit of 0.017 U mL−1 at a signal to noise ratio of 3. Furthermore, the proposed method can also be applied for the evaluation of PKA inhibition and PKA activity assay in cell samples. Therefore, the proposed biosensor shows great promise as a universal tool for diagnostics and drug discovery of PKA-related diseases. Electrochemical assay of PKA activity based on Zr4+-mediated DNAzyme-driven DNA walker amplification strategy. [Display omitted] • An electrochemical biosensor is developed for PKA activity assay. • The biosensor is constructed based on Zr4+ mediated DNAzyme-driven DNA walker signal amplification strategy. • The biosensor exhibits wide linear range and low detection limit for PKA assay. • This method can serve as a new tool for PKA assay in cell samples and inhibitor screening. [ABSTRACT FROM AUTHOR]

Naked-eye readout colorimetric signal-based assays are promising for high-throughput screening detection and point-of-care diagnostics in resource-constrained regions. Here, a novel direct competitive plasmonic enzyme-linked immunosorbent assay (dc-pELISA) based on gold nanoparticle (AuNP) aggregation with highly sensitive and robust naked-eye readout signal was developed and used to detect fumonisin B 1 (FB 1 ). AuNP aggregation was induced by a horseradish peroxidase (HRP)/hydrogen peroxide (H 2 O 2 )/tyramine (TYR) system, resulting in a dramatic color change from red to blue. In this system, H 2 O 2 was produced via GOx-mediated glucose oxidation reaction, and FB 1 –GOx was used as a competitive antigen. The proposed pELISA demonstrated good linear detection of FB 1 from 3.125 ng mL −1 to 25 ng mL −1 with a vivid color change from deep blue to red and a cutoff limit of 12.5 ng mL −1 observed by the naked eye. The average recoveries for FB 1 -spiked corn samples ranged from 76.5% to 96.8% with a relative standard derivation of 4.88~ 16.4%. Meanwhile, the proposed method exhibited excellent agreement (R 2 = 0.927) with the conventional ELISA method in blindly detecting FB 1 spiked corn samples. Additionally, the results of the proposed method for FB 1 positive corn samples also showed a high consistency with those of the ultra performance liquid chromatography method. These results indicated acceptable accuracy and precision of the proposed colorimetric ELISA for quantitative detection of FB 1 in actual corn samples. [ABSTRACT FROM AUTHOR]

Herein, we present a novel sandwich fluorescence enzyme linked immunosorbent assay (ELISA) for highly sensitive detection of Hepatitis B virus surface antigen (HBsAg) based on glucose oxidase (GOx)-induced fluorescence quenching of mercaptopropionic acid-modified CdTe quantum dots (MPA-QDs). In this system, hydrogen peroxide (H 2 O 2 ) sensitive MPA-QDs was used as a signal output, and glucose oxidase (GOx) was used as label which can generate H 2 O 2 via catalytic oxidation of glucose. The proposed method showed dynamic linear detection of HBsAg both in the range of 47 pg mL −1 ~ 380 pg mL −1 and 0.75 ng mL −1 ~ 12.12 ng mL −1 . The detection limit of the proposed fluorescence ELISA was 1.16 pg mL −1 , which was approximately 430-fold lower than that of horseradish peroxidase (HRP)-based conventional ELISA. The average recoveries for HBsAg-spiked serum samples ranged from 98.0% to 126.8% with the relative standard derivation below 10%, thus indicating acceptable precision and high reproducibility of the proposed fluorescence ELISA for HBsAg detection. Additionally, the developed method showed no false positive results analyzing 35 real HBsAg-negative serum samples, and exhibited excellent agreement (R 2 =0.9907) with a commercial time-resolved fluorescence immunoassay (TRFIA) kit for detecting 31 HBsAg-positive serum samples. In summary, the proposed method based on fluorescence quenching of H 2 O 2 sensitive QDs is considerably to be an excellent biodetection platform with ultrahigh sensitivity, good accuracy and excellent reliability. [ABSTRACT FROM AUTHOR]

The research and applications of immobilized enzyme reactors (IMERs) have become more and more widespread due to the numerous advantages like reusability, easy handling, prolonged lifetime, easy separation from products and substrate specificity. The miniaturized form of these reactors (microchip IMERs) received outstanding attention due to their special features and advantages over the traditional, larger analytical systems. Large specific surface is essential for the efficient operation of the microreactors, thus these devices include one of the several types of porous solid supports, but in this work only the particle based microchip IMERs are reviewed. A very large variety of micro- or nanoparticles (beads) have been used in the microchip IMERs, however, incorporating these particles into microchips is still a challenge, because the common procedures used for the preparation of chromatographic columns are not well applicable at the microscopic level. Many detection systems were applied with microchip IMERs using on-chip or off-chip arrangement. The combination of microchip IMERs with mass spectrometry is particularly popular, because in these systems high-throughput analysis can be achieved by which the proteomic studies can be largely accelerated. In most chip IMER-MS systems, the chips are used for sample pretreatment including analyte (protein) digestion, preconcentration of analyte, removal of matrix materials. Additional applications of the IMERs - like the rapid protein digestion with proteolytic enzymes, the transformation of analytes to a more easily or more sensitively measurable form (detection signal amplification) and the design of microarrays/biosensors to analyze antigens based on specific interactions in immunoanalytical studies – are also reviewed. [ABSTRACT FROM AUTHOR]

Novel amperometric bi-enzyme biosensor based on tyrosinase (Tyr)-catalyzed L -tyrosine polymerization to effectively immobilize Tyr and glucose oxidase (GOx) simultaneously has been developed and is demonstrated to be efficient in monitoring multi-analyte (bisphenol A (BPA), phenol, Cr(III), glucose, and Cr(VI)). For the first time, the polymer from L-tyrosine oxidation (PLT) was utilized to in-situ immobilize biomacromolecules and was demonstrated to be effective in entrapping high-load and high-activity enzymes. The prepared bi-enzyme biosensor (PLT-Tyr-GOx/Au electrode) works well in the biosensing of glucose (GOx substrate) and Cr(VI) (GOx inhibitor), and also exhibits excellent performance in Tyr substrates (BPA and phenol) and Tyr inhibitor (Cr(III)) sensing. In addition, the resultant biosensor exhibits excellent stability, precision, high sensitivity and fabrication simplicity, which may find wide applications in diversified fields including biotechnology. [ABSTRACT FROM AUTHOR]

Cytochrome c (Cyt c ) has been used as a model protein to investigate the characters of modified electrodes by many researchers. It has been also employed to construct biosensors to detect hydrogen peroxide, nitrate, superoxide, and etc. Cyt c immobilization techniques, including physical adsorption, entrapment in hydrogel or polymers, layer-by-layer assembly, Langmuir–Blodgett, and covalent attachment are discussed followed by various electrochemical methods applied in the electrode modification. The exploration of some modified protein electrodes, for example, screen printed, microperoxidase and engineered Cyt c are also presented. The preparation, characterizations and some properties of nanocomposites to modify electrode surface for immobilizing Cyt c are highlighted. This review is attempted to discuss the influences of the physical and chemical properties of the substrate materials, such as specific area and surface charge on the protein loading and electron transfer of Cyt c briefly. The comparative information of Cyt c -based electrochemical modified electrodes, such as average surface coverage, sensitivity, linear range, and detection limit of the analyte of interest is also summarized. [ABSTRACT FROM AUTHOR]

Vascular endothelial growth factor (VEGF) is a crucial signaling protein for the tumor growth and metastasis, which is also acted as the biomarkers for various diseases. In this research, we fabricate an aptamer-antibody sensor for point-of-care test of VEGF. Firstly, target VEGF is captured by antibody immobilized on the microplate, and then binds with aptamer to form the sandwich structure. Next, with the assist of glucose oxidase (GOx)-functionalized ssDNAs, hybridization chain reaction occurs using the aptamer as the primer. Thus, GOx are greatly gathered on the microplate, which catalyzes the oxidization of glucose, leading to the pH change. As a result, the detect limit at a signal-to-noise was estimated to be 0.5 pg/mL of target by pH meter, and 1.6 pg/mL of VEGF was able to be distinguished by naked eyes. Meanwhile, this method has been used assay VEGF in the serum with the satisfactory results. [ABSTRACT FROM AUTHOR]

Near-field communication (NFC) was used to control a portable glucose biosensor for diabetes diagnosis. The system comprised a smartphone and an NFC potentiostat connected to a screen-printed carbon electrode (SPCE) modified with Prussian blue-graphene ink and functionalized with gold nanoparticles-embedded poly (3,4ethylene dioxythiophene):polysulfonic acid coated with glucose oxidase (GOx-AuNPs-PEDOT:PSS/PB-G). GOx catalyzed the glucose redox reaction while the conductivity and sensitivity of the AuNPs-PEDOT:PSS composite enhanced electron transfer to the PB‐G, which was used as a mediator. The fabrication process was characterized by scanning electron microscopy (SEM) with energy dispersibe x-ray analysis (EDX). The platform was electrochemically characterized by electrical impedance spectroscopy (EIS) and cyclic voltammetry (CV). The NFC biosensing device was then applied to quantify glucose in human blood serum by amperometry. The linear concentration range and detection limit for glucose were 0.5–500 μM and 0.15 μM, respectively. The accuracy of the device was good and results were in agreement with the results obtained from the standard hospital method. This NFC glucose sensing device can be a simple, sensitive, selective and portable platform for medical diagnosis. [Display omitted] • A smartphone-based biosensor was developed for real-time diabetes diagnosis. • Prussian blue mediates a glucose oxidase-catalyzed redox reaction. • The device exhibited good linearity and selectivity with a low detection limit. • Near-field communication transmits blood glucose data at point of care. [ABSTRACT FROM AUTHOR]

Cancer is one of the leading causes of death worldwide and a crisis for global health. Breast cancer is the second most common cancer globally. In the perusal, a novel electrochemical biosensor amplified with hierarchical flower-like gold, poly (n-butyl acrylate), and MXene (AuHFGNs/PnBA-MXene) nanocomposite and activated by highly special antisense ssDNA (single-stranded DNA) provide a promising alternative for miRNA-122 detection as a biomarker of breast cancer. The biosensor presented a detection limit of 0.0035 aM (S/N = 3) with a linear range from 0.01 aM to 10 nM. The platform was tried on 20 breast cancer miRNAs extracted from actual serum specimens (10 positives and 10 negatives). Founded on the quantitatively obtained outcomes and statistic analysis (t -test, box-graph, receiver performance characteristic curve, and cut-off amount), the biosensor showed a meaningful discrepancy between the native and positive groups with 100% specificity and 100% sensitivity. While, RT-qPCR showed less specificity and sensitivity (70% specificity, 100% sensitivity) than the proposed biosensor. To assess the quantitative capacity and biosensor detection limit for clinical tests, the biosensor diagnosis performance for continually diluted miRNA extracted from patients was compared to that gained by RT-qPCR results, indicating that the biosensor detection limit was lower than RT-qPCR. ssDNA/AuHFGN/PnBA-MXene/GCE displayed little cross-reaction with other sequences and also showed desirable stability, reproducibility, and specificity and stayed stable until 32 days. As a result, the designed biosensor can perform as a hopeful method for diagnosis applications. [Display omitted] • An AuHFGNS/PnBA-MXene as a signal amplifier for a novel detection of breast cancer. • The biosensor exhibited excellent sensitivity with a LOD of 0.0035 aM. • The biosensor showed 100% sensitivity and specificity for the analysis of serum samples. [ABSTRACT FROM AUTHOR]

Protein biosensors hold a promise to transform the way we collect physiological data by enabling quantification of biomarkers outside of specialized laboratory environment. However, achieving high specificity and sensitivity in homogeneous assay format remains challenging. Here we report construction of fluorescent biosensor arrays based on artificial allosteric α-amylase-activated PQQ-dependent glucose dehydrogenase (Amy-GDH). Amy-GDH was covalently immobilized on silica nanoparticles that were then arrayed on fiberglass sheets. The activity of the biosensor was monitored using a smartphone camera via emergence of bright fluorescence (λ ex 365 nm) originating from reduced phenazine methosulfate upon glucose oxidation by Amy-GDH. We show that such biosensor arrays demonstrate an apparent K d of 115 pM for α-amylase with a detection limit of 2 pM. Using the developed biosensor arrays, we were able to specifically and accurately quantify the concentration of α-amylase in biological fluids such as serum and saliva. We propose that the presented approach can enable construction of ultrasensitive point-of-care diagnostic arrays. [Display omitted] • Chimeric enzymes with artificial allostericity • Biosensing with the use of a smartphone for point-of-care pplications. • Stress biomarker analysis in biofluids. • Amplified output signals. [ABSTRACT FROM AUTHOR]

A reagent-less amperometric glucose biosensor operating in not-stirred sample solution was developed. A working electrode of the designed biosensor was based on a graphite rod (GR) electrode, which was modified with 1,10-phenanthroline-5,6-dione (PD) and glucose oxidase (GOx). The PD and the GOx were layer-by-layer adsorbed on the GR electrode surface with subsequent drying followed by chemical cross-linking of the adsorbed GOx with glutaraldehyde (GA). Optimal preparation conditions of the working electrode (GR/PD/GOx) were achieved with 12.6 μg and 0.24 mg loading amount of PD and GOx, respectively and 25 min lasting cross-linking of the GOx with GA. A current response to glucose of the GR/PD/GOx electrode was measured at +200 mV potential vs Ag/AgCl reference electrode. Maximum current response was registered when the pH of the buffer solution was 6.0. The registered current response to glucose was linear in the concentration range of 0.1–76 mmol L –1 (R 2 =0.9985) and a detection limit was 0.025 mmol L –1 . The GR/PD/GOx electrode demonstrated good reproducibility and repeatability with the relative standard deviation of 6.2% and 1.8% (at 4.0 mmol L –1 of glucose), respectively, high anti-interference ability to uric and ascorbic acids. It was highly selective to glucose and demonstrated good accuracy in the analysis of human serum samples. [ABSTRACT FROM AUTHOR]

A highly sensitive and recyclable surface-enhanced Raman scattering (SERS) chip sensor is designed for the determination of silver ions. It is based on the specific reversible binding between silver ions and glucose oxidase (GOD). The sensing chip is made by layer-by-layer assembling GOD on a metal nanoparticle-assembled, SERS-active chip with a positive charged polyelectrolyte as a linker. Iso-alloxazine, a chromophore in flavin adenine dinucleotide (FAD) in GOD, coordinates with silver ions, which causes significant variation in SERS spectra of GOD. The reaction shows high sensitivity and selectivity for silver ions with the detection limit of 1.0×10 −10 M. Most significantly, the bonded Ag(I) in GOD can be reduced to Ag(0) by sodium borohydride and the GOD structure can be recovered then. Thus, the chip sensor is recyclable. Merits of using GOD as a novel SERS probe toward Ag + are embodied in not only a simplified sensor structure based on its dual role of Ag + accepter and SERS signal reporter, but also a nontoxic label to biological systems, indicating that it is promising for tracing Ag + in vivo. [ABSTRACT FROM AUTHOR]

We report a novel amperometric glucose biosensor based on glucose oxidase (GOx) immobilized on a carbon nanotube (CNTs)–poly(diallyldimethyl-ammonium chloride) (PDDA)–platinum nanoparticle (PtNPs) modified carbon-paste electrode (CNTs–PDDA–PtNPs/CPE). The CNTs–PDDA–PtNPs composite materials were characterized by TEM and electrochemical techniques. Cyclic voltammetric results reveal direct electron transfer of the immobilized GOx, indicated by two quasi-reversible redox peaks at a potential of 0.37 V (vs. Ag/AgCl) in phosphate buffered solution (PBS) (0.10 M, pH 7). The biosensor provides good glucose oxidation activity and retention of GOx electrocatalytic activity due to CNTs–PDDA–PtNPs enhancement of the redox response. The carbon paste electrode was installed as working electrode in a flow through electrochemical cell of a flow injection (FI) system. Glucose was quantified using amperometric measurements at 0.5 V vs. Ag/AgCl and PBS carrier (0.10 M, pH 7.0) at a flow rate of 1.0 mL min −1 . The linear working ranges for glucose measurements were 0.1–3 mM ( r 2 =0.995) and 5–100 mM ( r 2 =0.997), with corresponding sensitivities of 0.127 and 0.060 (μA s) mM −1 , respectively. The system provides good precision of 2.8% R.S.D with a calculated detection limit (3 S/N) of 15 μM. The proposed method was successfully applied to determination of glucose in food and pharmaceutical samples with throughput of 200 samples h −1 . [ABSTRACT FROM AUTHOR]

Single or few-layer nanosheets of MoS 2 (MoS 2 nanosheets) and a composite composed of MoS 2 nanosheets, Au nanoparticles (AuNPs) and hemin (HE) (denoted as MoS 2 -Au-HE) were prepared. The composites possessed high synergetic catalysis activity towards the electroreduction of hydrogen peroxide. Furthermore, glucose oxidase (GOD) and AuNPs were used as marker of the complementary DNA (cDNA) strand of kanamycin aptamer to prepare a conjugate (reffered as cDNA-Au-GOD) that was designed as the signal probe. Both cDNA-Au-GOD and MoS 2 -Au-HE were applied to fabricate aptasensor for kanamycin. MoS 2 -Au-HE acted as solid platform for kanamycin aptamer and signal transmitters. AuNPs were employed as the supporter of cDNA and GOD which catalyze dissolved oxygen to produce hydrogen peroxide in the presence of glucose. Then cathodic peak current of H 2 O 2 was recorded by differential pulse voltammetry (DPV). The electrochemical reduction of H 2 O 2 was catalyzed by MoS 2 -Au-HE that was modified onto the surface of a glassy carbon electrode (GCE). The cathodic peak current of H 2 O 2 was highly linearly decreased with an increase of kanamycin concentrations from 1.0 ng/L to 1.0×10 5 ng/L, with a detection limit of 0.8 ng/L. This aptasensor can be used to detect kanamycin in milk with high specificity, sensitivity and selectivity. [ABSTRACT FROM AUTHOR]

Architecture design is widely regarded as a rational strategy to enhance the sensing performance of electrocatalysts. Herein, the novel three-dimensional hybrids based on Au and Cu 2 O were successfully synthesized via steps of in-situ growth, including anodic oxidation, annealing and galvanic displacement. Cu 2 O appeared in the morphology of nanowire array on conductive substrate, and was decorated by Au nanoparticles. Benefiting from the unique architecture and binder-free fabrication process, the Au/Cu 2 O nanowire arrays possessed high conductivity and abundant exposed active sites, as well as facilitated the direct electron transfer among detection object, electrocatalyst and current collector. Moreover, Au/Cu 2 O particles as contrast were fabricated to clarify the effect of structure on sensing ability. The Au/Cu 2 O nanowire arrays drove the glucose electro-oxidation reaction with great catalytic activity, in which a potential as low as 0.4 V was needed to reach a high sensitivity of 2.098 mA mM−1 cm−2. The excellent selectivity, stability and reproducibility were also obtained by the sensor. Furthermore, the quantitative detection of glucose level in diluted human serum were performed and the satisfactory result make the obtained sensor have the potential for practical applications. [Display omitted] • A facile and sensitive electrochemical sensor was fabricated by steps of in-situ growth. • The glucose sensor was modified with binder-free Au/Cu 2 O nanowire arrays. • The designed sensor featured high sensitivity at low detection potential. • Developed sensor displayed the feasibility in diluted blood glucose detection. [ABSTRACT FROM AUTHOR]