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Glucose oxidase has great potential as a bio-catalyst for the determination of glucose and H2O2 concentration, but it is sensitive to environmental influences and has poor recoverability. To overcome this limitation, this study presents a promising approach, i.e., glucose oxidase interposed with dopamine and ZIF-8 to develop a highly efficient and stable bio-catalyst for H2O2 production while determining glucose concentrations. The successful synthesis of GOx@ZIF-8/PDA was verified by SEM, EDS, XRD, FTIR, XPS, and UV analyses; GOx@ZIF-8/PDA exhibited higher stability, better reproducibility, and excellent glucose assay potential compared with the free enzyme. After 7 days of storage, GOx@ZIF-8/PDA almost maintained its initial activity, and the catalytic activity remained at 92.15 ± 2.13% after five consecutive applications. This study provides a new strategy for the preparation of highly active and stable immobilized enzymes. [ABSTRACT FROM AUTHOR]

Effective continuous glucose monitoring solutions require consistent sensor performance over the lifetime of the device, a manageable variance between devices, and the capability of high volume, low cost production. Here we present a novel and microfabrication-compatible method of depositing and stabilizing enzyme layers on top of planar electrodes that can aid in the mass production of sensors while also improving their consistency. This work is focused on the fragile biorecognition layer as that has been a critical difficulty in the development of microfabricated sensors. We test this approach with glucose oxidase (GOx) and evaluate the sensor performance with amperometric measurements of in vitro glucose concentrations. Spincoating was used to deposit a uniform enzyme layer across a wafer, which was subsequently immobilized via glutaraldehyde vapor crosslinking and patterned via liftoff. This yielded an approximately 300 nm thick sensing layer which was applied to arrays of microfabricated platinum electrodes built on blank wafers. Taking advantage of their planar array format, measurements were then performed in high-throughput parallel instrumentation. Due to their thin structure, the coated electrodes exhibited subsecond stabilization times after the bias potential was applied. The deposited enzyme layers were measured to provide a sensitivity of 2.3 ± 0.2 μA mM−1 mm−2 with suitable saturation behavior and minimal performance shift observed over extended use. The same methodology was then demonstrated directly on top of wireless CMOS potentiostats to build a monolithic sensor with similar measured performance. This work demonstrates the effectiveness of the combination of spincoating and vapor stabilization processes for wafer scale enzymatic sensor functionalization and the potential for scalable fabrication of monolithic sensor-on-CMOS devices. [ABSTRACT FROM AUTHOR]

This study introduces the development of a photothermal-based microfluidic paper analytical device (PT-µPAD) integrated with near-field communication (NFC) technology and smartphone readout for enzyme-free glucose quantification in human samples. With the properties of gold nanoparticles (AuNPs) both as a nanozyme and as a photothermal substrate, there is no need for costly reagents like enzymes or a readout instrumentation for the selective and sensitive detection of glucose. In PT-µPADs, AuNPs are etched by hydrogen peroxide (H2O2) generated from glucose catalysis. Photothermal detection from the plasmonic heating of these AuNPs when illuminated by a 533nm LED light source is achieved by inserting the PT-µPAD sensor into a portable NFC platform suitable for smartphone readout. Temperature variation is directly proportional to the glucose concentration. After optimization, we acquired a linear range between 5.0 and 20.0 µmol L−1 (R2 = 0.9967) and a limit of detection (LOD) of 25.0 nmol L−1 for glucose. Additionally, while our sensor does not utilize any enzyme, it is remarkably selective to glucose with no effects from interferences. Recovery studies in various human control samples indicated a range of 99.73–102.66% with the highest RSD of 3.53%, making it highly accurate and precise. Moreover, our method is more sensitive than other methods relying on conventional µPADs for glucose sensing. By integrating the potential benefits of microfluidics, nanomaterials as nanozymes, and NFC technology for wireless readout, our sensor demonstrates great promise as an accessible, affordable, and shelf-stable device for glucose quantification. Moreover, this concept can be extended to detect other molecules of interest as a point-of-care (POC) diagnostics device. [ABSTRACT FROM AUTHOR]

Safe, accurate, and reliable analysis of urinary biomarkers is clinically important for early detection and monitoring of the progression of chronic kidney disease (CKD), as it has become one of the world's most prevalent non-communicable diseases. However, current technologies for measuring urinary biomarkers are either time-consuming and limited to well-equipped hospitals or lack the necessary sensitivity for quantitative analysis and post a health risk to frontline practitioners. Here we report a robust paper-based dual functional biosensor, which is integrated with the clinical urine sampling vial, for the simultaneous and quantitative analysis of pH and glucose in urine. The pH sensor was fabricated by electrochemically depositing IrOx onto a paper substrate using optimised parameters, which enabled an ultrahigh sensitivity of 71.58 mV pH-1. Glucose oxidase (GOx) was used in combination with an electrochemically deposited Prussian blue layer for the detection of glucose, and its performance was enhanced by gold nanoparticles (AuNPs), chitosan, and graphite composites, achieving a sensitivity of 1.5 μA mM-1. This dual function biosensor was validated using clinical urine samples, where a correlation coefficient of 0.96 for pH and 0.98 for glucose detection was achieved with commercial methods as references. More importantly, the urine sampling vial was kept sealed throughout the sample-to-result process, which minimised the health risk to frontline practitioners and simplified the diagnostic procedures. This diagnostic platform, therefore, holds high promise as a rapid, accurate, safe, and user-friendly point-of-care (POC) technology for the analysis of urinary biomarkers in frontline clinical settings. [ABSTRACT FROM AUTHOR]

17β-Estradiol (E2) is an important endogenous estrogen, which disturbs the endocrine system and poses a threat to human health because of its accumulation in the human body. Herein, a biofuel cell (BFC)-based self-powered electrochemical aptasensor was developed for E2 detection. Porous carbon nanocage/gold nanoparticle composite modified indium tin oxide (CNC/AuNP/ITO) and glucose oxidase modified CNC/AuNP/ITO were used as the biocathode and bioanode of BFCs, respectively. [Fe(CN)6]3− was selected as an electroactive probe, which was entrapped in the pores of positively charged magnetic Fe3O4 nanoparticles (PMNPs) and then capped with a negatively charged E2 aptamer to form a DNA bioconjugate. The presence of the target E2 triggered the entrapped [Fe(CN)6]3− probe release due to the removal of the aptamer via specific recognition, which resulted in the transfer of electrons produced by glucose oxidation at the bioanode to the biocathode and produced a high open-circuit voltage (EOCV). Consequently, a "signal-on" homogeneous self-powered aptasensor for E2 assay was realized. Promisingly, the BFC-based self-powered aptasensor has particularly high sensitivity for E2 detection in the concentration range of 0.5 pg mL−1 to 15 ng mL−1 with a detection limit of 0.16 pg mL−1 (S/N = 3). Therefore, the proposed BFC-based self-powered electrochemical aptasensor has great promise to be applied as a successful prototype of a portable and on-site bioassay in the field of environment monitoring and food safety. [ABSTRACT FROM AUTHOR]

Glucose oxidase (GOx) catalyzes the oxidation of D -glucose to D -glucono-1,5-lactone and has a wide range of applications in various industries. However, the strict substrate specificity of GOx hampers its application in the conversion of other abundant sugars such as D -xylose. In this study, the substrate preference of GOx from Aspergillus niger (AnGOx) was engineered using a semi-rational design approach. The mutant T110V/F414L exhibited a 5.7-fold increase in D -xylose oxidation activity compared to that of the wild-type enzyme, which was attributed to its enhanced affinity for the substrate. Molecular dynamics simulations indicated that the T110V and F414L mutations may mitigate the non-productive binding of D -xylose at the entrance of the substrate-binding pocket, and therefore, are beneficial for providing access of its C1 hydroxyl group to the catalytic residues. Moreover, the mutant simultaneously oxidized D -xylose and D -glucose in the corncob hydrolysate to the corresponding aldonic acids when coupled with catalase. These findings provide new insights into substrate recognition by GOx and offer a new method for the utilization of D -xylose from lignocellulosic feedstocks. [ABSTRACT FROM AUTHOR]

Recently protein binders have emerged as a promising substitute for antibodies due to their high specificity and low cost. Herein, we demonstrate an electrochemical biosensor chip through the electronic labelling strategy using lead sulfide (PbS) colloidal quantum dots (CQDs) and the unnatural SARS-CoV-2 spike miniprotein receptor LCB. The unnatural receptor can be utilized as a molecular probe for the construction of CQD-based electrochemical biosensor chips, through which the specific binding of LCB and the spike protein is transduced to sensor electrical signals. The biosensor exhibits a good linear response in the concentration range of 10 pg mL−1 to 1 μg mL−1 (13.94 fM to 1.394 nM) with the limit of detection (LOD) being 3.31 pg mL−1 (4.607 fM for the three-electrode system) and 9.58 fg mL−1 (0.013 fM for the HEMT device). Due to the high sensitivity of the electrochemical biosensor, it was also used to study the binding kinetics between the unnatural receptor LCB and spike protein, which has achieved comparable results as those obtained with commercial equipment. To the best of our knowledge, this is the first example of using a computationally designed miniprotein receptor based on electrochemical methods, and it is the first kinetic assay performed with an electrochemical assay alone. The miniprotein receptor electrochemical biosensor based on QDs is desirable for fabricating high-throughput, large-area, wafer-scale biochips. [ABSTRACT FROM AUTHOR]

Nanozymes, as artificial enzymes, overcome the low catalytic efficiency, poor stability, and cost-effectiveness of previous artificial enzymes. In this work, vanadium carbide@vanadium oxide (V2C@VOx) nanosheets were synthesized by a one-pot hydrothermal method using V2C as a precursor and H2O2 as an oxidant. The prepared V2C@VOx nanosheets exhibited excellent multi-enzyme activity such as peroxidase-like activity, superoxide dismutase-like activity, and oxidase-like activity. The entire synthetic process of V2C@VOx nanosheets does not need any additional intercalation agent, strong acid, or base. Meanwhile, the synthesized method of nanozymes was simple, time-saving, and environmentally friendly. In particular, based on the multi-enzyme activity of V2C@VOx nanosheets, the nanozymes catalyzed H2O2 and dissolved O2 to oxidize 3′,3,5,5′-tetramethylbenzidine (TMB). Additionally, glucose reacted with glucose oxidase (GOx) to form H2O2 under water bath conditions. Therefore, the colorimetric sensing strategy of glucose was constructed based on the multi-enzyme activity of V2C@VOx nanosheets and the enzymatic reaction of glucose. The detection limit of the sensor was as low as 0.08 μM. Furthermore, the colorimetric method was successfully used to detect glucose in human serum. The sensor exhibited low cost, high stability, and easy construction. Overall, this work proposed a promising strategy based on novel vanadium-based nanozymes with excellent multi-enzyme activity for biomedical detection. [ABSTRACT FROM AUTHOR]

Nanoscale metal–organic frameworks (NMOFs) with peroxidase-mimicking activity emerged as promising antibacterial agents instead of antibiotics. Therefore, here, a novel 2D bimetallic NMOF-based antibacterial agent named Al/Fe-TCPP NMOF/GOx was constructed. Compared with the Fe-TCPP NMOF, the obtained Al/Fe-TCPP NMOF exhibited significantly improved water-solubility, which favors the production and diffusion of hydroxyl radicals (˙OH). Glucose oxidase (GOx) loaded on Al/Fe-TCPP NMOF catalyze exogenous glucose to produce gluconic acid and hydrogen peroxide (H2O2), which provided an acidic environment to enhance the peroxidase-like activity of Al/Fe-TCPP NMOF and provided H2O2 for producing ˙OH to kill bacteria. Meanwhile, Fe3+ in Al/Fe-TCPP NMOF/GOx can deplete GSH, which increases the concentration of ˙OH for improving the antibacterial efficiency. The result of the antibacterial experiment in vitro demonstrated that Escherichia coli (E. coli) and Staphylococcus aureus (S. aureus) were nearly completely killed in the co-incubation of Al/Fe-TCPP NMOF/GOx and glucose in vitro whereas the viabilities of E. coli and S. aureus were still higher than 50% in the presence of GOx and glucose, which illustrated that the 2D bimetallic Al/Fe-TCPP NMOF/GOx + glucose possesses excellent antibacterial action on typical E. coli and S. aureus. [ABSTRACT FROM AUTHOR]

There is a need for flexible chemical sensors for the ecological and physiological research of avian species such as house sparrows (Passer domesticus). Current methods in this field are invasive and require multiple physical interactions with the birds. Emerging research in flexible bioelectronics can enable realization of implantable devices that are mechanically compliant with the underlying tissues for continuous real-time sensing in situ. However, challenges still remain in forming an intimate flexible interface. One of the promising flexible bioelectronic platforms for tissue-embedded sensing is based on functionalizing surgical sutures or threads. Threads have three-dimensional flexibility, high surface-area-to-volume ratio, inherent wicking properties, and are easily functionalizable using reel-to-reel dip coating. Threads are ideal as they are lightweight, therefore, would not interfere with flight motion and would only require minimal interaction with the bird. However, the challenge remains in achieving a highly conductive yet flexible electrode for electrochemical sensing using materials such as gold. In this study, we address this issue through novel gold deposition directly on thread substrate followed by enzyme immobilization to realize flexible electrochemical glucose biosensors on medical-grade sutures. These sensors were calibrated and tested in a range that is wide enough to include the expected range of glucose concentration in house sparrows (0–8.55 mM). Glucose monitoring in house sparrows will provide insights into energy metabolism and regulation during stress responses. In addition, the stability, repeatability, and selectivity of the sensor were tested with final validation in a real bird. Our innovative gold-coated, thread-based flexible electrochemical glucose sensor can also be used in other small and large animals. This can also be extended to monitoring other metabolites in future. [ABSTRACT FROM AUTHOR]

In this study, vanillin was applied to yield 2-O-propargyl coniferin, onto which alkynyl groups could be introduced at sites that do not participate in dehydrogenation polymerization (ortho position of the benzene ring), thus avoiding changes in the structure of the lignin side chains and functional groups on the benzene ring. In order to evaluate whether these synthetic monomers can effectively participate in the biosynthesis of lignin, five different dehydrogenation polymers (DHPs) were generated with the help of β-glucosidase, glucose oxidase and peroxidase. The results showed that, compared with DHP synthesized from a monomer without alkynyl labeling, the basic structure of DHP synthesized from 2-O-propargyl coniferin was not changed. Therefore, the alkynyl-labeled lignin monomer 2-O-propargyl coniferin showed good biocompatibility, and it might participate in the biosynthesis of plant lignin while having negligible impact on the structure of lignin. The designed lignin monomer could provide a new idea for the research of the plant lignification process. [ABSTRACT FROM AUTHOR]

A novel photoelectrochemical (PEC) sensor was constructed, using Fe2TiO5 nanodisks under visible-light irradiation, for the determination of glucose in human blood serum. The uniformly dispersed Fe2TiO5 nanodisks were synthesized for the first time by an ion exchange method and subsequent heat treatment. As excellent catalysts, the Fe2TiO5 nanodisks can directly catalyze the oxidation of glucose to produce current in the absence of glucose oxidase. Compared with commercial TiO2, the Fe2TiO5 nanodisks exhibit better activity in the electrocatalytic oxidation of glucose and can generate a photocurrent as a signal for glucose detection. The PEC sensor shows a wide linear range (4 μM–10 mM), a low limit of detection (0.588 μM) and a super sensitivity of 2653 μA mM−1 cm−2, which are much better than similar configurations reported previously. This PEC sensor has been successfully used to monitor glucose in human blood serum. Moreover, this PEC glucose sensor based on Fe2TiO5 nanodisks possesses great potential for application in point-of-care clinical diagnosis. [ABSTRACT FROM AUTHOR]

Two-dimensional metal–organic framework nanosheets are attractive as peroxidase mimicking nanocatalysts due to their rich chemical functional groups, large surface area, high porosity, and accessible active sites. In this study, we synthesized FeCu bifunctional 2D MOF nanosheets using a solvothermal method. Fe and Cu ions were added as metal precursors, while organic amine and acid served as the organic ligands to construct the FeCu-MOF nanosheets. These nanosheets demonstrated robust peroxidase-like catalytic activities and were employed to develop a visual detection system for multiple targets, such as glucose and kanamycin. In the detection mechanism, glucose was oxidized into gluconic acid by glucose oxidase (GOx), leading to the generation of H2O2. When H2O2 is present, the FeCu-MOF NSs demonstrate high intrinsic peroxidase-like activity, which might catalytically oxidize 3,3′,5,5′-tetramethylbenzidine (TMB) into a blue-coloured oxTMB product with a strong UV absorption at 654 nm. Subsequently, kanamycin was added to the above sensing system. The kanamycin strongly interacted with the FeCu-MOF NSs through H-bonding and blocked electron transfer, resulting in a colour change of the solution from blue to colourless with a weak UV absorption at 654 nm. Under the optimal conditions, the proposed colorimetric sensor exhibits an excellent linear response to glucose and kanamycin over the 0.25–5 μM and 0.02–0.1 μM ranges, respectively. The proposed colorimetric assay detection limits for glucose and kanamycin were found to be as low as 0.1 μM and 8 nM, respectively, and such a sensor shows excellent selectivity and sensitivity against different potential interferents. Thus, our proposed colorimetric assay was satisfactory when applied to glucose and kanamycin detection in agricultural and livestock husbandry samples. [ABSTRACT FROM AUTHOR]

We present the formation of a cheap and environmentally friendly working electrode material for glucose biosensors with good catalytic properties. The classic electrode in such devices consists of a conductive material modified with the enzyme glucose oxidase. The working principle is the electrochemical detection of hydrogen peroxide as a product of the enzymatic transformation of glucose. As a base material, we offer manganese dioxide; it is a natural highly selective catalyst for the decomposition of H2O2 and is electrochemically deposited onto the surface of ITO. We approached the formation of MnO2 films systematically. By changing parameters such as the deposition method, pH of the electrolyte, and the drying temperature of the precipitate, a series of electrodes were formed. These electrodes were characterized by SEM, electrochemical impedance spectroscopy, and XPS and their electrocatalytic activity was studied. Significant differences in the sensitivity of the electrodes were detected. The manganese dioxide film with the best catalytic characteristics is formed in the electrolyte with pH 1 by cyclic voltammetry and then drying at 60 °C. The surface of the electrode was then modified with a solution of GOx enzyme with a concentration of 2 mg ml-1 (100-250 units per mg solid). The sensitivity of such an electrode is 117.8 μA mmol-1 cm-2. The range of determined concentrations of glucose is from 0.1 mM to 3 mM. The sensitivity is comparable to that of electrodes based on expensive materials such as graphene and noble metals. [ABSTRACT FROM AUTHOR]

An electrochemical glucose sensor based on flexible materials is significant for wearable devices used for real-time health monitoring and diagnosis. However, applying flexible electrodes involves complex fabrication processes and might reduce detection sensitivity. To overcome these obstacles, we herein report a novel strategy for preparing a highly flexible enzyme electrode based on an electrospun poly(vinyl alcohol) (PVA) mat decorated with in situ grown silver nanoparticles (nano-Ag) for electrochemical glucose sensing. Ferrocene (Fc) was selected as an electron acceptor for glucose oxidase (GOD) in order to minimize the influence of oxygen. Electron transfer between GOD and Fc was facilitated by confining them within a mixed self-assembled monolayer (SAM) formed on a thin layer of gold deposited on top of the PVA/nano-Ag film. Nano-Ag was found to significantly increase the surface area of the electrode and improve the stability of electrode conductivity during tensile deformation. Electrochemical glucose detection was performed by chronoamperometry in the electroactivity domain of ferrocene, and good linearity (R2 = 0.993) was obtained in the range of 0.2–7 mM with a detection limit of 0.038 mM and a relative standard deviation (RSD) of 1.45% (n = 6). After being stuck to a bendable PDMS slice and bent, respectively, at 30° and 60° 50 times, the electrode showed slight changes in detection results (<4.78%), which remained within 8% when the bending angle increased to 90°. With its high flexibility, good detection performance, and convenient fabrication process, the proposed enzyme electrode showed good potential as a flexible platform for wearable glucose sensing systems. [ABSTRACT FROM AUTHOR]

Diabetes and impaired glucose regulation (IGR) threaten the lives and health of numerous patients. Interstitial fluid (ISF) glucose, displaying an excellent correlation with blood glucose, is highly desired to address the limitations of invasive and minimally invasive glucose detection. Herein, we present a screen-printed iontophoretic biosensing system to extract ISF noninvasively and perform in situ instant glucose detection. A three-dimensional graphene aerogel combined with Prussian blue (GA@PB) was introduced as an electron mediator, providing suitable support for glucose oxidase (GOx) immobilization, highly boosting the detection sensitivity. Additionally, a self-made diffuse cell and an ex vivo model were developed to demonstrate the efficacy of ISF extraction based on reverse iontophoresis technology. Highly sensitive and accurate detection of ISF glucose could be achieved with an LOD of 0.26 mM over a 0–15 mM range. Finally, tests on healthy volunteers were conducted to further validate the feasibility of this as-proposed system. Combined with its well flexible and biocompatible features, it holds considerable prospects in the development of wireless wearable biosensors for continuous blood glucose monitoring. [ABSTRACT FROM AUTHOR]

This study involves the fabrication of a sandwich-type electrochemical immunosensor for sensitive and simultaneous detection of alpha-fetoprotein (AFP) and cancer embryo antigen (CEA). Gold nanoparticle (Au NP)–modified ultrathin metal–organic framework nanosheets (UMOFNs) were prepared (denoted as Cu-UMOFNs@Au NPs and Co-UMOFNs@Au NPs). Furthermore, the Cu-UMOFNs@Au NPs and Co-UMOFNs@Au NPs were used as redox probes to label different antibodies. Subsequently, any potential active sites that remained were blocked using glucose oxidase. Dual catalysis amplification was achieved using the prepared MOF-derived materials via in situ catalysis of glucose to produce H2O2 in the presence of glucose oxidase. H2O2 was further catalyzed by Cu-UMOFNs@Au NP- and Co-UMOFNs@Au NP-derived materials to obtain better signal responses. The results revealed that the linear range of the proposed immunosensor for the simultaneous detection of AFP was 0.001–100 ng mL−1 (detection limit, 0.28 pg mL−1; S/N = 3) and that for the simultaneous detection of CEA was 0.001–80 ng mL−1 (detection limit, 0.31 pg mL−1; S/N = 3). Notably, the proposed method promises rapid, simple, and cost-effective analysis of biological samples. [ABSTRACT FROM AUTHOR]

In this study, we present a facile and inexpensive colorimetric sensor for hydrogen peroxide (H2O2) and glucose based on the formation of an Fe3+ complex assisted by the Fenton reaction in a micellar medium. The mechanism of the sensor is based on the Fenton reaction occurring between the added H2O2 and ferrous ion (Fe2+) probe, which was stabilized by complexing with dithizone (Dz) before forming a micelle with the non-ionic surfactant Triton X-114 (TX-114). The extremely reactive hydroxyl radical (˙OH), the by-product of the Fenton reaction, exhibited much stronger oxidizing ability than H2O2, and thus strongly oxidized the stabilized Fe2+ ion, thereby accelerating the spectrophotometric response of the Fe3+ ion after coordinating with the thiocyanate ion (SCN−). The obtained absorbance of the Fe3+ and SCN− complex was related to the concentration of H2O2. Under the optimal condition, the micelle probe of Fe2+ exhibited good stability, without transforming to Fe3+ within 24 h. The sensor achieved an LOD of 5 μM and provided a linear range of 10 μM–4.0 mM for H2O2 determination. When coupled with glucose oxidase to generate a biosensing system, glucose was changed to H2O2 and could be measured down to 10 μM within a linear range of 10 μM–4.0 mM. The interferences naturally found in human blood plasma at the physiological level had no obvious effects on the glucose biosensor. According to the comparison with the hexokinase-spectrophotometric method used by hospitals, the results obtained from the proposed method for glucose measurements in human plasma samples were in good agreement (p > 0.05). This indicated the enormous potential of combining the Fenton reaction and micellar system-stabilized metal ion complex probes to design sensors for the alternative detection of H2O2 and glucose. [ABSTRACT FROM AUTHOR]

The unique catalytic properties of enzymes have led to the production of useful medicinal intermediates, foods, and biofuels from sustainable sources. However, the instability of soluble/free enzymes under several challenging conditions (e.g., pH, proteolysis, temperature, ionic potential, chemical denaturants) restricts the use of enzyme-based biocatalysts. Encapsulation of enzymes on suitable carriers would mitigate the instability issues faced in robust biocatalysis. An "ideal" carrier material employed for protein immobilization should be nontoxic, scalable, biocompatible, and should not compromise the biological activity and structure of proteins/enzymes. Thus, biodegradable and renewable biomass-derived functional materials (BDFMs) are envisaged as promising carriers for enzymes. BDFMs have in-built chemical functionalities and desirable physicochemical properties that enable their use in enzyme catalysis at the industrial scale. Numerous BDFMs have been used as immobilization matrices to improve the biocatalytic activity and stability of various enzymes. These solid materials are renewable and environmentally friendly compared with synthetic polymers. This review highlights the advancements, challenges and prospects in the emerging field of BDFMs (cellulose, silk protein, chitin, chitosan, lignocellulose, and a combination of biopolymers such as chitin/lignin and chitosan/alginate) for immobilization of enzymes (e.g., α-chymotrypsin, cytochrome c, carbonic anhydrase, glucose oxidase, ribonuclease, cholesterol oxidase, alkaline phosphatase, β-glucosidase, lipase, horseradish peroxidase, catalase, tyrosinase, acetylcholinesterase, amylase, invertase, protease, laccase, β-galactosidase, and several others) for biocatalytic processes. This review also describes the relationship between the structural properties and functionality of several enzymes immobilized in BDFMs, and profiles the impact of pH, temperature, reusability, stability of storage, and the activity of these enzymes. Future perspectives in this promising field, as well as potential difficulties, are discussed. This review will help in refining biocatalysis technologies whereby biomass-derived, environmentally friendly materials are employed as enzyme supports. [ABSTRACT FROM AUTHOR]

Herein, we report an indocyanine green (ICG)-decorated and glucose oxidase (GOx)-loaded nanoscale composite COF material via a stepwise post-synthetic modification. The obtained GOx@COF-ICG can achieve synergistic inhibition of intracellular heat defense systems through starvation therapy to enhance photothermal therapy of tumors. [ABSTRACT FROM AUTHOR]

In this study, an ultrasensitive electrochemical miRNA-21 biosensor is described. Manganese dioxide-gold nanoparticle (MnO2-Au NP) nanoconjugates were employed as sensing base materials, miRNA-21 was selected as a model analyte, and hybridization chain reaction (HCR) was employed to form long DNA concatemers using two different oligonucleotides with a complementary sequence. Thus, lots of biotin were loaded on DNA concatemers and one of them was labelled with biotin at its 3′ terminal. The biosensor was designed as follows: a sulfhydryl-hairpin probe (HP) was first dropped on the surface of the glassy carbon electrode (GCE) modified with MnO2-Au NP nanoconjugates (HP/MnO2-AuNPs/GCE). After it was treated with MCH, the modified electrode was hybridized with miRNA-21, resulting in the loop of HP being opened to form a vertical structure. Subsequently, the modified electrode (miRNA-21/HP/MCH/MnO2-AuNPs/GCE) was incubated with DNA concatemers to form a sandwich structure of HP-miRNA-21-DNA concatemers on the modified electrode surface. Finally, the streptavidin-HRP conjugates were linked to the sandwich structure by specific recognition interaction between biotin and avidin. Differential pulse voltammetry (DPV) was used to measure the electrochemical response of the biosensor in the phosphate-buffered solution (0.10 M PBS, pH 7.0) containing 2.0 mM hydroquinone (HQ) and 1.8 mM H2O2. As a result, a larger reductive signal was obtained at a potential of −0.17 V (vs. SCE). Various experimental conditions were optimized, including solution pH, incubation time, and the amount of DNA concatemers. Under optimal conditions, the biosensor showed good sensing performance, such as a wide linear response range (0.1 fM and 100 nM) and low detection limit (0.063 fM, at S/N = 3). Meanwhile, the biosensor can discriminate single base matched miRNA-21, indicating that the biosensor had good selectivity. [ABSTRACT FROM AUTHOR]

Covalent organic frameworks (COFs) are crystalline porous polymers with the characteristics of a large specific surface area, controllable pore structures, high stability, and low mass density. Herein, we demonstrate the development of an exogenous coreactant-free electrochemiluminescent sensor based on a hydrazone-linked COF for sensing glucose. We synthesized a TFPPy-DMeTHz-COF with the hydrazone bond as the linkage and 2,5-dimethoxyterephthalohydrazide (DMeTHz) and 1,3,6,8-tetrakis(4-formylphenyl)pyrene (TFPPy) as the monomers. The obtained TFPPy-DMeTHz-COF exhibits high electrochemiluminescence (ECL) efficiency (21.7%) without either the addition of any coreactants or the removal of dissolved O2, and the ECL signal intensity of the TFPPy-DMeTHz-COF is 6.6 and 113-fold higher than those of TFPPy and DMeTHz, respectively. The enhanced ECL emission of the TFPPy-DMeTHz-COF is induced by OH− in PBS, and the ECL signal exhibits linear dependence on the pH value in the range from 3 to 10. When glucose is present, the addition of glucose oxidase (GOx) to the O2-containing solution generates gluconic acid, and the resultant gluconic acid can induce the decrease of the pH value and the quenching of the ECL emission of the TFPPy-DMeTHz-COF. This exogenous coreactant-free electrochemiluminescent sensor exhibits good selectivity, excellent stability, and high sensitivity with a limit of detection (LOD) of 0.031 μM, and it can accurately detect glucose in human serum. [ABSTRACT FROM AUTHOR]

The formation of new carbon–nitrogen bonds is indisputably one of the most important tasks in synthetic organic chemistry. Here, nitroso compounds offer a highly interesting reactivity that complements traditional amination strategies, allowing for the introduction of nitrogen functionalities via ene-type reactions or Diels–Alder cycloadditions. In this study, we highlight the potential of horseradish peroxidase as biological mediator for the generation of reactive nitroso species under environmentally benign conditions. Exploiting a non-natural peroxidase reactivity, in combination with glucose oxidase as oxygen-activating biocatalyst, aerobic activation of a broad range of N-hydroxycarbamates and hydroxamic acids is achieved. Thus both intra- and intermolecular nitroso-ene as well as nitroso-Diels–Alder reactions are performed with high efficiency. Relying on a commercial and robust enzyme system, the aqueous catalyst solution can be recycled over numerous reaction cycles without significant loss of activity. Overall, this green and scalable C–N bond-forming strategy enables the production of allylic amides and various N-heterocyclic building blocks utilizing only air and glucose as sacrificial reagents. [ABSTRACT FROM AUTHOR]

Bio-activity conservation of biomolecules after immobilizing in nanomaterials has been a tough challenge, especially in biomedical applications. Herein, we developed a novel freezing-assisted reverse microemulsion method to encapsulate water-soluble enzymes in hollow mesoporous silica nanospheres (HMSNs) for maximumly maintaining enzyme bio-activity. Firstly, a low-temperature and ethanol-free synthesis was carried out, and glucose oxidase (GOx) as a model enzyme was encapsulated into HMSNs to obtain GOx@HMSNs. The TEM and SEM images showed a uniform sphere morphology of GOx@HMSNs with a large hollow cavity for GOx loading. The element mapping, FTIR spectrum and TGA curve further confirmed the effective physical encapsulation of GOx in HMSNs, which can maintain stable bio-activity as verified by the enzyme activity assay. In addition to the facile synthesis for avoiding enzyme-denaturation, the N2 adsorption–desorption curves further demonstrated that small mesopores on HMSNs for blocking enzyme leakage may be another important factor for conserving GOx activity. Finally, GOx@HMSNs as a biosensor significantly possessed a wider linear range of 0.06 mM to 2.61 mM with a low detection limit of 0.01 mM, indicating high sensitivity. Therefore, our synthesis method provides a promising approach for biomolecule immobilization with potent bio-activity and biosensor applications with superior sensitivity. [ABSTRACT FROM AUTHOR]

Diabetics often prick their fingertips to measure the glucose levels in their blood. However, this traditional method not only causes prolonged pain but also increases the risk of infection. Hence, in this study, a non-invasive flexible glucose biosensor with high sensitivity was fabricated. Specifically, NiCo metal–organic frameworks (NiCo-MOFs) served as the electrode material of a micro-supercapacitor and sensing material of a glucose sensor. The electrochemical tests verified that the prominent sensitivity of the NiCo bimetal product is 1422.2 μA mM−1 cm−2. The micro-supercapacitor based on the as-fabricated NiCo-MOFs showed a high energy density of 11.5 mW h cm−2 at the power density 0.26 mW cm−2. In addition, the as-designed glucose device exhibited an excellent sensitivity of 0.31 μA μM−1. Furthermore, a flexible energy storage and glucose detection system was successfully prepared by further integrating the micro-supercapacitor and glucose sensor. The smart detector could accurately and conveniently measure the glucose concentration in sweat in real-time. Therefore, the wearable real-time sensing device displays feasible application for non-invasive glucose monitoring and health management. [ABSTRACT FROM AUTHOR]

Diabetes is a chronic disease affecting 10% of the population globally, and can lead to serious damage in the heart, kidneys, eyes, blood vessels or nerves. Commercial artificial closed-loop feedback systems can significantly improve diabetes management and save lives. However, they are large and expensive for users. Here, we demonstrate for the first time a wearable, minimally-invasive, fully electrochemically-controlled feedback minisystem for diabetes management. Both the working principles of the sensor and pump in the feedback system are based on electrochemical reactions. The smart minisystem was constructed based on integrating the thermoplastic polyurethane hollow microneedles with an electrochemical biosensing device on its outer layer and an electrochemical micropump facing the inner layer of the microneedles. The sensing device was constructed based on sputtering thin metal films through a shadow mask and electroplating Prussian blue on the surface of the microneedles, followed by the immobilization of glucose oxidase on the working electrode. The electrochemical micropump was constructed by sputtering the interdigital electrodes, followed by sealing with a thin elastic film, which was further integrated with the inner channels of the microneedles. Both the sensor and the pump were electrically powered. Via being controlled by a printed circuit board, the biosensing device monitored the levels of interstitial glucose continuously to drive the electrochemical pump to deliver insulin intelligently, in order to control blood glucose within the normal range. The closed-loop feedback system was studied for its capability in maintaining the blood glucose levels of diabetic rats under various physiological conditions. The utility of the intelligent feedback system was successfully demonstrated on diabetic rats for controlling the blood glucose levels within the normal range. The minisystem is wearable, small, cost-effective, precise, stable and painless. It is anticipated that this approach opens a new paradigm for the development of closed-loop diabetes minisystems and may lead to a compelling future for diabetes management. [ABSTRACT FROM AUTHOR]

Currently, the co-immobilization of multi-enzymes on a solid carrier and their applications in cascade catalytic reactions are primarily studied. In this study, a MOF/polymer porous membrane composed of DUT-5 incorporated polyvinylidene fluoride (PVDF) is constructed and employed in the co-immobilization of porcine pancreatic lipase (PPL) and glucose oxidase (GOx) for the first time. The loading amounts of DUT-5 nanoparticles were varied to optimize the subsequent immobilization efficiency for the two enzymes. The adsorption conditions, isotherms and kinetics for both PPL and GOx were investigated systematically, and the optimum adsorption conditions were determined and used in the co-immobilization of the two enzymes step by step. It is interesting that the maximum adsorption amounts for the two enzymes in the co-immobilization process are similar to the results obtained in the single enzyme immobilization, which indicates the better compatibility of PPL and GOx in the hybrid membranes. The catalytic activities of the co-immobilized enzymes were evaluated using a cascade oxidation reaction, in which H2O2 produced in the GOx-catalyzed oxidation of glucose worked as the oxidant in the subsequent oxidation of styrene. Further, the catalytic efficiency of the co-immobilized enzymes is compared to that of the mixed free PPL and GOx. The improved catalytic rates and better reusability of the co-immobilized enzymes highlight the broader applications of MOF-based membranes in the co-immobilization of two or more enzymes and the catalytic applicabality in the cascade organic reactions. [ABSTRACT FROM AUTHOR]

Herein, a gold nanoparticles/graphene aerogels (AuNPs/GAs) modified electrochemical biosensor with catalytic hairpin assembly (CHA) and Y-shaped DNA nanostructure dual-signal amplification approaches for ultrasensitive microRNA-21 (miR-21) detection was successfully constructed, which displayed an ultra-wide detection linear range from 5 fM to 50 nM, as well as a relatively low detection limit (LOD) of 14.70 aM (S/N = 3). Furthermore, the sensing strategy had excellent specificity among highly homologous miRNA family members and exhibited satisfactory analytical performance for miRNA detection. [ABSTRACT FROM AUTHOR]

Lanthanide-doped inorganic nanocrystals have attracted extensive attention due to their long luminescence lifetime and large Stokes shift. In this work, an immunosensing platform based on CePO4:Tb (CPOT) was successfully constructed, which could avoid the autofluorescence interference of complex biological matrices. Specifically, CPOT was synthesized by a solvothermal method, which exhibited H2O2-responsive luminescence behavior. Taking advantage of this feature, an autofluorescence-free immunosensor with CPOT as the probe and H2O2 as the quencher was developed to detect prostate-specific antigen (PSA). Functionalized liposomes were used to encapsulate glucose oxidase (GOD) and labeled on detection antibodies to improve the sensitivity of the probe. Under the proven optimal experimental conditions, the developed autofluorescence-free immunosensor exhibited a linear luminescence response to the logarithm of PSA concentration (0.005–25 ng mL−1) with a limit of detection (LOD) of 3.25 pg mL−1. The performance shows that the autofluorescence-free immunosensor based on this strategy opens up a new field of vision for clinical PSA detection. [ABSTRACT FROM AUTHOR]

In this study, Ni nanoparticles were grown on a silver-coated nylon yarn (SCNY) surface by electrochemical deposition to prepare SCNY@Ni. The hierarchical Ni–Ag nanostructure promoted their synergistic effect, which enhanced the electrocatalytic behavior of glucose oxidation. The test result of SCNY@Ni showed its high sensitivity (115.26 μA mM−1 cm−2 and 67.37 μA mM−1 cm−2) with a wide linear response (from 2 μM to 1 mM and from 1 mM to 22 mM) of glucose con-centration range, a low detection limit (LOD) of 2 μM, fast response time (3 s), and good selectivity for glucose determination in the presence of sucrose (SU), aceta-mino phenol (AP), D -fructose (D -Fru), ascorbic acid (AA), dopamine (DA), hydro-quinone (HQ) and uric acid (UA) as potential interference species. Also, SCNY@Ni exhibited excellent stability, repeatability, reproducibility and flexibility. It has good prospects for large-scale production. [ABSTRACT FROM AUTHOR]

Graphdiyne (GDY) is an sp and sp2 co-hydrocarbon allotrope whose particular structure endows it with many fascinating properties, including abundant chemical bonds, high conjugation, natural pores, high carrier mobility, high conductivity and stability, etc. In this work, two-dimensional graphdiyne is prepared as an electrode substrate material coupling with an exonuclease III-assisted amplification strategy to construct a superior-performance self-powered biosensor based on enzymatic biofuel cells for highly sensitive detection of the tumour marker miRNA-21. Glucose oxidase (GOD) is first immobilized on the GDY/AuNP composite to prepare a bioconjugate. GDY/AuNP modified carbon cloth is used as an enzyme biofuel cell electrode, which is then modified with bilirubin oxidase as a biocathode. The bioconjugate binds to GOD through specific binding to the bioanode. When miRNA-21 is present, specific recognition by exonuclease III in the system results in cleavage of the capture probe, and miRNA-21 is recovered and involved in the cycle. The target miRNA-21 then causes corresponding changes in the open-circuit voltage of the self-powered system. Based on this, a sensitive detection method was constructed, within the scope from 0.1 fM to 0.1 nM with a shallow detection limit of 55.2 aM (S/N = 3). The new approach triumphantly has been used to detect miRNA-21 in serum, which provides a compelling new way for early diagnosis of related cancers. [ABSTRACT FROM AUTHOR]

3D-printing has become a fundamental part of research in many areas of investigation since it provides rapid and personalized production of parts that meet very specific user needs. Biosensing is not an exception, and production of electrochemical sensors that can detect a variety of redox mediators and biologically relevant molecules has been widely reported. However, most 3D-printed electrochemical sensors detailed in the literature rely on big, individual, single-material electrodes that require large sample volumes to perform effectively. Our work exploits multi-material fused filament fabrication 3D-printing to produce a compact electrochemical sensor able to operate with only 100 μL of sample. We report cyclic voltammetry, differential pulse voltammetry, and chronoamperometry results to assess sensor performance and sensitivity. We investigated the influence of layer print orientation and layer thickness on the electrochemical performance of the sensor, and used the optimal parameters to produce the final device. The integrated 3D-printed platform successfully detects electrochemical activity for hexaammineruthenium(III) chloride and potassium ferricyanide (0.1 mM to 2 mM in 100 mM KCl), dopamine (50 μM to 1 mM in 1×PBS), and glucose via mediated amperometric glucose oxidase enzyme-based sensing (1 mM to 12 mM in 1×PBS), indicating good acceptance of biological modification. These results reveal the exciting potential of multi-material 3D-printing and how it can be used for the rapid development of efficient, small, integrated, personalized electrochemical biosensors. [ABSTRACT FROM AUTHOR]

Glucose oxidase (GOx) triggered starvation therapy has attracted great attention in cancer treatment, which is tremendously inhibited under a tumor hypoxia environment. Here a neutrophil membrane camouflaged hybrid nanozyme (GOx/HPB/NEM) is fabricated based on hollow Prussian blue loaded with GOx for enhanced starvation/photothermal tumor therapy. The hybrid nanozyme possesses catalase properties that originated from Prussian blue to produce oxygen from H2O2, which consequently reacts with glucose catalyzed by GOx. Thus GOx-driven oxidation effectively eliminates glucose inside tumors for starvation therapy. Meanwhile, adenosine triphosphate (ATP) production in tumor cells is inhibited, accompanied by heat shock protein (HSP) depletion. Furthermore, hollow Prussian Blue (HPB) mediated photothermal therapy (PTT) is coupled with GOx-mediated starvation therapy to obtain more effective tumor therapy. The neutrophil membrane on the nanozyme surface helps noninvasive tumor active targeted accumulation. In vivo studies demonstrate that the GOx/HPB/NEM nanozyme presents remarkable capability in tumor ablation with a tumor growth inhibition rate of 97.7%. The proposed treatment paradigm may encourage more hybrid nanozyme nanoplatforms involving effective cancer therapy. [ABSTRACT FROM AUTHOR]

In this research, dual-strategy biosensing of glucose was proposed based on multifunctional CuWO4 nanoparticles (CuWO4 NPs), which were prepared for the application of electrochemical and colorimetric sensing of glucose. CuWO4 NPs show large specific surface area and good conductivity as well as excellent peroxidase-like activity. A sensitive and selective electrochemical glucose biosensor was fabricated with the immobilization of glucose oxidase (GOx) on a CuWO4 NP modified electrode for enhancing the direct electron transfer behavior. A wide linear range of 0.005–1.8 mM with a low detection limit of 1.5 μM and a high sensitivity of 28.02 mA M−1 cm−2 were achieved by using the electrochemical biosensor. Meanwhile, a colorimetric and visual glucose biosensor was constructed based on the GOx/CuWO4 cascade nanozyme, which shows a linear range of 0.05–1.0 mM with excellent selectivity. CuWO4 NPs as a promising matrix open up a dual-strategy biosensor for sensitive and selective detection of glucose. [ABSTRACT FROM AUTHOR]

Chemodynamic therapy (CDT) can convert endogenous hydrogen peroxide (H2O2) to highly reactive hydroxyl radical (˙OH) through Fenton or Fenton-like reaction to kill tumor cells, which is a promising anticancer strategy. However, the limited H2O2 and overexpressed glutathione (GSH) in tumor cells make CDT ineffective. Here, an efficient nanocomposite, UCN@CuO2–GOx (UCCuG), was synthesized, realizing both starvation therapy and H2O2 self-supplying CDT in vitro. In this case, the glucose oxidase (GOx) of the nanocomposite could consume glucose for starvation therapy after the UCCuG nanocomposite entered tumor cells. In addition, the acidic environment of the lysosome triggered the release of Cu2+ and H2O2 by the decomposition of UCCu; then, Cu2+ was reduced to Cu+ by GSH in tumor cells; and finally, Cu+ catalyzed the released H2O2 to generate ˙OH for CDT. The in vitro experiments demonstrated starvation-enhanced CDT with remarkable results. Meanwhile, under 980 nm laser irradiation, the upconversion luminescence signal of UCN in the UCCuG nanocomposite was reduced due to the CuO2–GOx coating, while it gradually recovered after the UCCuG nanocomposite reacted with glucose and GSH under the tumor microenvironment (TME). Such a luminescent intensity recovery process is expected to monitor the TME-activated therapeutic effect in real time. This strategy may solve the problem of insufficient CDT efficacy caused by limited endogenous H2O2 and overexpressed GSH in tumor cells. This multifunctional nanocomposite demonstrates the promising application of starvation-enhanced CDT in tumor treatment. [ABSTRACT FROM AUTHOR]

A smartphone-based photochemical biosensor capable of realizing multiplex detection of glucose, uric acid (UA), and total cholesterol (TC) is reported here for the first time. The system was composed of a photochemical dongle, a cloud-enabled smartphone, and disposable test strips. The dongle was controlled using a microcontroller unit and was designed to convert the reflected light's intensities into optoelectronic signals for analytes quantification. Only 30 μL of the fingertip blood is needed to complete accurate and reliable measurements within 2 minutes. A cloud-enabled smartphone is connected to the dongle via Bluetooth to serve as a data receiver, and users can obtain the test results for proactive health management or remote diagnosis, while powering the dongle. We believe the proposed biosensor will contribute a lot to the point-of-care-testing and has promising prospects in contributing to the development of the Internet of Medical Things. [ABSTRACT FROM AUTHOR]

There exists great potential in combining heterogeneous metallic nanoparticle active sites and enzymatic active sites for sequentially catalysed chemical transformations. This study provides an illustrative system where glucose oxidase and gold nanoparticles are successfully combined into a hybrid catalytic material. This multi-site catalyst is used to convert glucose to a more valuable saccharic acid product without the need for a strong oxidant such as H2O2, hypochlorite, or nitric acid to be externally added. We synthesise a hybrid material that is able to oxidise glucose to gluconic acid and H2O2 with glucose oxidase, and gold catalyses the further oxidation to saccharic acid. The in situ generation of H2O2 provides a proximal, dilute oxidizing agent for further oxidation. It is observed that higher pH promotes H2O2 decomposition and saccharic acid generation catalysed by the gold nanoparticles. A 33% yield of saccharic acid in 90 minutes is observed without the addition of nitric acid, harsh oxidants, above ambient temperatures, or high oxygen pressures. The results demonstrate a cooperative reaction cascade system that opens new possibilities for metal nanoparticle-enzyme hybrid materials that can be applied to catalytic biomass conversion in mild reaction conditions. [ABSTRACT FROM AUTHOR]

Molecular tags such as fluorophores are increasingly being replaced with nanoparticles thanks to their superior optical properties, substantial chemical stability, and stability against photobleaching. Herein, we innovatively constructed a new ratiometric fluorescence enzyme-linked immunosorbent assay (RF-ELISA) for the screening of alpha-fetoprotein (AFP) in early hepatocellular carcinoma in vitro diagnostics using carbon dots@SiO2@CdTe quantum dots (CDs@SiO2@CdTe QDs). Carbon dots with blue fluorescence were initially encapsulated into SiO2 nanospheres through the typical Stöber method. Thereafter, CdTe QDs with red fluorescence were modified onto the surface of CDs@SiO2 nanospheres. Dual-emission nanotags with blue and red fluorescent signals were utilized to design a RF-ELISA method for the determination of AFP on the anti-AFP capture antibody-coated microplate using glucose oxidase (GOx)-labeled anti-AFP secondary antibody. After the formation of the sandwiched immunocomplex, GOx catalyzed glucose to generate hydrogen peroxide (H2O2), which could quench the red fluorescence of CdTe QDs on the surface of nanotags. Meanwhile, the encapsulated carbon dots in the nanotags could still maintain the initial blue fluorescence intensity. The ratio between red fluorescence intensity and blue-emission intensity could be used for the quantitative monitoring of AFP concentration under optimum conditions. The experimental results indicated that CDs@SiO2@CdTe QDs-based RF-ELISA could exhibit a good fluorescence signal with a dynamic linear range of 0.05–60 ng mL−1 at a low detection limit of 8.7 pg mL−1. Moreover, the fluorescence color of the solution including CDs@SiO2@CdTe QDs changed from pink to purple to blue with the increasing AFP level when viewed by the naked eye. Good reproducibility, high specificity, and acceptable stability were achieved for the analysis of target AFP. Importantly, the accuracy of ratiometric fluorescence immunoassay was evaluated to determine human serum samples, giving well-matched results relative to commercially usable human AFP ELISA method. [ABSTRACT FROM AUTHOR]

Glucose detection is of great significance in the fields of clinical analysis and the food industry. Herein, a visual and portable method was developed for detecting glucose via hydrogen peroxide (H2O2) test strips. Once glucose oxidization was catalyzed by glucose oxidase (GOD) to produce H2O2, the color of the H2O2 test strip changed obviously. There is a good linearity for the glucose response in the range of 0.01–0.5 mM, and the limit of detection (LOD) reached as low as 0.02 mM by the naked eye. The GOD-functionalized H2O2 test strip was used to detect glucose in one step within 2 min. The specific catalytic oxidation of glucose by GOD ensured the high specificity for detecting glucose. The cost was calculated as within $ 0.62 per measurement. Therefore, it provides a facile, rapid and low-cost visual bioassay for glucose point-of-care testing (POCT). [ABSTRACT FROM AUTHOR]

A lucigenin and riboflavin chemiluminescence system was utilized for the first time to achieve the "turn-on" detection of tyrosinase activity via an in situ reaction between tyrosinase and tyramine to generate dopamine. Tyramine is the model substrate of tyrosinase and dopamine is the product. Since dopamine can enhance the chemiluminescence of the lucigenin and riboflavin system, the chemiluminescence of lucigenin and riboflavin can be enhanced in the presence of both tyramine and tyrosinase. In the presence of 6.0 U mL−1 tyrosinase, the chemiluminescence intensity was nearly 10 times higher than that of lucigenin, riboflavin and tyramine mixtures. Therefore, this method has been applied in the chemiluminescence "turn-on" detection of tyrosinase activity in the range of 0.1–8.0 U mL−1 with the limit of detection (LOD) of 0.028 U mL−1. This overall process of sensing tyrosinase activity took nearly 30 min. Moreover, it had high selectivity in the chemiluminescence "turn-on" detection of tyrosinase activity towards other enzymes, such as glucose oxidase, lysozyme, trypsin or alkaline phosphatase. When 1.0, 2.0 and 5.0 U mL−1 tyrosinase were added to the diluted serum samples, recoveries were in the range of 100.2%–104.1%. This indicates that this method for the chemiluminescence "turn-on" detection of tyrosinase activity has high sensitivity, selectivity, accuracy and fast response time. [ABSTRACT FROM AUTHOR]

With the aid of an exonuclease-powered DNA walker, the amount of glucose oxidase immobilized on the bioanode can be facilely tailored by varying the concentration of microRNA-141, so a glucose/O2 biofuel cell is employed as a self-powered sensor for sensitive and selective detection of microRNA-141. [ABSTRACT FROM AUTHOR]

Efficient urchin-like Pt nanoparticles@Bi2S3 (PtNPs@Bi2S3) composite materials were prepared by a composite soft template synthesis of urchin-like Bi2S3 and then the microwave-assisted growth of PtNPs onto the Bi2S3 nanostructure. For the first time, an accurate electrochemical glucose biosensor was fabricated via immobilizing glucose oxidase (GOx) on PtNPs@Bi2S3. The PtNPs@Bi2S3 composite was investigated via scanning electron microscopy, electrochemical impedance spectroscopy, Fourier transform infrared spectroscopy, and cyclic voltammetry. The PtNPs@Bi2S3 composite provides a large surface area to load a large number of enzyme molecules, which maintains the biological activity. PtNPs loaded on Bi2S3 enhanced the conductivity and improved the direct electron transfer of the proposed biosensor with the synergistic effect. The fabricated electrochemical biosensor possesses high sensitivity, and a wide linear range from 0.003 mM to 0.1 mM and 0.1 mM to 1.9 mM. Moreover, the biosensor has outstanding stability, superior selectivity and good repeatability, which can be utilized to monitor the glucose level in practical human serum. The PtNPs@Bi2S3 composite supplies a special matrix for immobilizing proteins and potential for establishing other effective biosensors. [ABSTRACT FROM AUTHOR]

Three-dimensional cell cultures using patient-derived stem cells are essential in vitro models for a more efficient and individualized cancer therapy. Currently, culture conditions and metabolite concentrations, especially hypoxia, are often not accessible continuously and in situ within microphysiological systems. However, understanding and standardizing the cellular microenvironment are the key to successful in vitro models. We developed a microfluidic organ-on-chip platform for matrix-based, heterogeneous 3D cultures with fully integrated electrochemical chemo- and biosensor arrays for the energy metabolites oxygen, lactate, and glucose. Advanced microstructures allow straightforward cell matrix integration with standard laboratory equipment, compartmentalization, and microfluidic access. Single, patient-derived, triple-negative breast cancer stem cells develop into tumour organoids in a heterogeneous spheroid culture on-chip. Our system allows unprecedented control of culture conditions, including hypoxia, and simultaneous verification by integrated sensors. Beyond previous works, our results demonstrate precise and reproducible on-chip multi-analyte metabolite monitoring under dynamic conditions from a matrix-based culture over more than one week. Responses to alterations in culture conditions and cancer drug exposure, such as metabolite consumption and production rates, could be accessed quantitatively and in real-time, in contrast to endpoint analyses. Our approach highlights the importance of continuous, in situ metabolite monitoring in 3D cell cultures regarding the standardization and control of culture conditions, and drug screening in cancer research. Overall, the results underline the potential of microsensors in organ-on-chip systems for successful application, e.g. in personalized medicine. [ABSTRACT FROM AUTHOR]

The accurate and sensitive detection of glucose from secretory clinical samples, such as tears and saliva, remains a great challenge. In this research, a novel ultrasensitive glucose detection method consisting of a glucose oxidase (GOx), pistol-like DNAzyme (PLDz), and CRISPR–Cas12a system is proposed. First, the oxidation of glucose catalyzed by GOx leads to the production of H2O2; the self-cleavage activity of PLDz is activated after recognition of the produced H2O2. The two procedures triggered by COx and PLDz play an important role in accurately identifying glucose and converting glucose signals to nucleic acids. The obtained PLDz fragments can be recognized by the Cas12 enzyme and thus activate the trans-cleavage activity of the Cas12a enzyme. Finally, the surrounding reporter probes are cut by the Cas12a enzyme to produce fluorescence signals. In summary, an ultra-sensitive and specific fluorescence method has been developed for glucose detection from secretory clinical samples, which could potentially contribute to the noninvasive diagnosis of diabetes mellitus. [ABSTRACT FROM AUTHOR]

Diabetes mellitus is a chronic disease that affects human health worldwide. Monitoring of glucose levels in the blood is still vital for the early clinical diagnosis and management of diabetes. Since single-wavelength fluorescence probes are prone to being influenced by instrument fluctuations, the design of simple and cheap ratiometric fluorescence probes is urgently needed for glucose determination. Silicon nanoparticles (SiNPs) possess excellent properties, such as biocompatibility, low toxicity and good water solubility, which makes them suitable for nanosensors. Herein, we synthesized SiNPs by a one-step method that simplifies the preparation procedure, and for the first time established a novel SiNP-based nanoprobe (denoted as SiNPs/OPD/HRP/GOx) for ratiometric fluorescence and visual detection of glucose. Glucose oxidase (GOx) catalyzes glucose to produce gluconic acid and hydrogen peroxide (H2O2) under appropriate conditions. The H2O2 can oxidize o-phenylenediamine (OPD) to generate 2,3-diaminophenazine (oxOPD) in the presence of horseradish peroxidase (HRP). The oxOPD has strong fluorescence and can quench the fluorescence of SiNPs by means of the inner filter effect. With elevated glucose concentration, the fluorescence of SiNPs decreases gradually, while the fluorescence of oxOPD increases, thus achieving ratiometric fluorescence detection of glucose. Likewise, the color change with increasing amounts of glucose realizes the visual detection of glucose. This SiNP-based nanoprobe has good selectivity toward glucose and a simple preparation approach, which provides a new method for establishing glucose sensors. [ABSTRACT FROM AUTHOR]

Surface-enhanced Raman scattering (SERS) is an ultrasensitive fingerprint spectroscopy technique. The combined application of SERS and nanozymes has shown excellent prospects in the field of biomedical diagnosis. In the present study, polyaniline@MoS2@Fe3O4@Au (PANI@MoS2@Fe3O4@Au) nanozymes were successfully prepared using hydrothermal reactions. PANI@MoS2@Fe3O4@Au nanozymes have not only dramatically enhanced the peroxidase-like activity but also significantly enhanced the SERS performance. We also studied the effect of different concentrations of HAuCl4·4H2O on the SERS activity of nanozymes and found that PANI@MoS2@Fe3O4@Au nanozymes prepared using 2 mg mL−1 HAuCl4·4H2O solution exhibited the best SERS performance. We used SERS to study the enzyme kinetics of the nanozymes, and the results showed that the nanozymes have a strong affinity for H2O2 and TMB. Finally, we combined PANI@MoS2@Fe3O4@Au nanozymes and glucose oxidase (GOx) to establish a SERS glucose biosensor, which has the advantages of ultrasensitivity, high-precision, and a wide linear response range. The linear response range of glucose is 10−11–10−3 M, and the detection limit is 10−12 M. More importantly, we have successfully determined the glucose content in human serum samples with satisfactory accuracy. This work provides an essential new strategy for designing composite nanozymes for biocatalysis and provides a new idea for constructing high-sensitivity SERS biosensors. [ABSTRACT FROM AUTHOR]

The artificial solid-state nanopore/nanochannel based electrochemical sensing technique has demonstrated great advantages such as high sensitivity and minimalized equipment. However, its application is largely hindered by complex routes and high expense for fabrication. Here, we develop low-cost and easily accessible channels based on natural wood and present a pathway to utilize the wood membrane for local electrochemistry applications. Inspired by the natural mineralization of wood, Prussian blue (PB), an artificial peroxidase (POD)-like mimetic, is mineralized in wood channels via a contra-diffusion technique. Using glucose enantiomers (L / D -Glu) as model analysts, a target-activated strategy is used for chiral molecule recognition by combining glucose oxidase (GOx) with PB-modified wood channels. In the as-proposed hybrid channels, GOx catalyzes the oxidation of only D -Glu to gluconic acid and H2O2. These products dramatically activate the POD-like activity of PB and further trigger the oxidation of the uncharged substrate 2,2′-azino-bis(3-ethylbenzothiazoline-6-sulfonate) (ABTS) to cationic species (ABTS˙+) in the channels. More importantly, benefitting from the confinement effect of the channel and the asymmetrical mineralization of PB, a significantly selective and sensitive identification of D -Glu is achieved. This study provides a promising way to use natural wood as a novel channel membrane to replace artificial channels for constructing electrochemical sensing platforms. [ABSTRACT FROM AUTHOR]

A novel hedgehog-shaped bismuth sulfide (HS-Bi2S3) nanostructure was for the first time explored as an electrode material for biosensing. Using cetyltrimethyl ammonium bromide (CTAB)-trimellitic acid as a composite soft template, the HS-Bi2S3 nanostructure was synthesized by a hydrothermal route. Using glucose oxidase (GOx) as the model, the HS-Bi2S3 nanostructure was employed to immobilize GOx for the development of a sensitive electrochemical glucose biosensor. The characterization of HS-Bi2S3 and the biosensor was performed by scanning electron microscopy, X-ray diffraction spectroscopy, Fourier transform infrared spectroscopy and cyclic voltammetry. The hedgehog-shaped nanostructure of Bi2S3 has a large specific surface area to trap a large number of enzyme molecules, and at the same time greatly enhances the direct-electron-transfer action of enzymes. The HS-Bi2S3-based biosensor shows a wide linear range of 0.005–1.7 mmol L−1 and a low detection limit of 1.6 μmol L−1 for glucose at −0.37 V, which presents much better assay performance in comparison with the glucose biosensor without HS-Bi2S3. The present electrochemical biosensor displays high selectivity, good repeatability and stability, which can be used to measure blood glucose in real serum samples. [ABSTRACT FROM AUTHOR]

MoS2 nanosheets (MoS2 NSs), which exhibited peroxidase-like activity, were prepared using the hydrothermal method. The microstructure and element speciation of the MoS2 NSs were characterized using transmission electron microscopy (TEM) and X-ray photoelectron spectroscopy (XPS), respectively. The obtained MoS2 NSs could catalyze the H2O2-mediated oxidation of 3,3′,5,5′-tetramethylbenzidine (TMB) to form blue oxidized TMB (ox TMB) with an absorption peak at 652 nm. The effects of MoS2 NS concentration, incubation time, temperature, and acidity on the color development of TMB were investigated. Under the optimal conditions (1.0 μg mL−1, 40 min, 40 °C, pH 4.0), the increase in absorbance, which was induced by MoS2 NS-catalyzed TMB oxidation, enabled the detection of H2O2 ranging from 2.5 μmol L−1 to 300 μmol L−1. As H2O2 is one of the products of glucose oxidase (Gox)-catalyzed glucose oxidation, a colorimetric method was further established for measuring the concentration of glucose. The absorbance response was linearly dependent on glucose concentration of 2.5–200 μmol L−1, with a detection limit of 2.1 μmol L−1. The proposed method was applied to the assay of glucose in urine samples with satisfactory results. [ABSTRACT FROM AUTHOR]

Tumor-related exosomes, which are heterogeneous membrane-enclosed nanovesicles shed from cancer cells, have been widely recognized as potential noninvasive biomarkers for early cancer diagnosis. Herein, an artificial enzyme cascade amplification strategy based on a switchable DNA tetrahedral (SDT) scaffold was proposed for quantification of breast cancer-derived exosomes. The SDT scaffold is composed of G-quadruplex mimicking DNAzyme sequences on its two single-stranded edges and glucose oxidase (GOx) on the four termini of the complementary strands. In the initial state, the SDT scaffold is blocked by the switch strand which consists of partial complementary domains with the DNA tetrahedron and a MUC1 aptamer. MCF-7 exosomes could release the quadruplex-forming sequences through the recognition of the MUC1 aptamer. The newly formed DNAzyme brings GOx into spatial proximity and induces high-efficiency enzyme cascade catalytic reactions on the SDT. Consequently, high sensitivity toward MCF-7 exosome analysis was obtained with a wide linear range of 3.8 × 106 to 1.2 × 108 particles per mL and a limit of detection of 1.51 × 105 particles per mL. In addition, such a DNAzyme reconfiguration strategy was able to distinguish MCF-7 exosomes from other breast cancer cell derived exosomes, indicating its excellent method specificity. The proposed enzyme cascade strategy not only provides a novel signal transformation and amplification nanoplatform for quantifying the specific populations of exosomes, but also can be further expanded to the analysis of multiple cancer biomarkers. [ABSTRACT FROM AUTHOR]