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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]