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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]

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]

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

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

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

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

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

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

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

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

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

Precise and sensitive microRNA (miRNA) analysis is very significant for early disease diagnosis. In this work, a dual DNA nanomachines-based homogeneous electrochemical biosensor was constructed for the sensitively ratiometric detection of miRNA by a nicking enzyme (Nt.AlwI)-assisted cycling signal amplification strategy. The Co-based metal organic frameworks (Co-MOFs) and toluidine blue (TB) were employed as signal probes and internal reference probes, respectively. The introduction of internal reference probes can actually calibrate the interferent factors of the analytical system to improve the stability in detection procedure. In addition, with the help of the magnetic separation technique, the homogeneous electrochemical biosensor provides a more simpler way for the development of immobilization-free electrochemical miRNA biosensors, avoiding the complex modification procedure of traditional electrochemical biosensing interfaces. Consequently, taking advantages of this proposed dual DNA nanomachines-based homogeneous electrochemical biosensor, the highly sensitive and selective detection of miRNA-141 as model could be accomplished in ranging from 1 fM to 10 nM with detection limit of 0.46 fM. This strategy exhited good sensitivity and stability to integrate the nicking enzyme-powered dual DNA nanomachines with the ratiometric electrochemical output modes, which open new opportunities for the sensitive and reliable diagnosis of miRNA-related diseases. In this work, a dual DNA nanomachines-based homogeneous electrochemical biosensor was constructed for the sensitively ratiometric detection of miRNA by a nicking enzyme (Nt.AlwI)-assisted cycling signal amplification strategy. The Co-based metal organic frameworks (Co-MOFs) and toluidine blue (TB) were employed as signal probes and internal reference probes, respectively. With the help of the magnetic separation technique, the homogeneous electrochemical biosensor provides a more simpler way for the development of immobilization-free electrochemical miRNA biosensors, avoiding the complex modification procedure of traditional electrochemical biosensing interfaces. [Display omitted] • Dual DNA nanomachine greatly contributed to the improved sensitivity for the miRNA analysis. • The self-correction advantage of the internal reference probe in ratiometric biosensors caused to the stable and reliable signals. • Homogeneous electrochemical biosensor provides a more simpler way for the development of immobilization-free electrochemical biosensors. [ABSTRACT FROM AUTHOR]

A facile amperometric biosensor that included oxidase mimicking Co/2Fe metal-organic framework (MOF) for sialic acid (SA) detection was prepared. Amperometric SA biosensor was constructed on a gold screen-printed electrode via immobilization of Co/2Fe MOF and N-acetylneuraminic Acid Aldolase (NANA-Aldolase) enzyme, respectively. NANA-Aldolase enzyme converts free SA into pyruvate and N-acetyl- d -mannosamine. After this conversion, oxidase mimicking Co/2Fe bimetallic MOF converts pyruvate into acetylphosphate and O 2 into H 2 O 2. Investigation of analytical characteristics resulted with the linear range of 0.02 mM–1.00 mM of SA concentration with limit of detection value of 0.026 mM. Sample application studies with developed SA biosensor were carried out with GD3 ganglioside and HeLa cancer cell lines which have high SA concentrations while A549 cell lines were also used as control group. Before detecting free SA, the bound SA was freed from SA sources where every step was monitored via electron impedance spectroscopy. Then, free SA was successfully detected with the amperometric SA biosensor and as a result, more practical and accurate system was developed. [Display omitted] • An amperometric sialic acid (SA) biosensor based on oxidase mimicking Co/2Fe metal-MOF was prepared. • The biosensor included Co/2Fe MOF and NANA-Aldolase enzyme immobilized on AuSPE. • MOF converts pyruvate into acetylphosphate and oxygen into H2O2. • With developed biosensor, free SA was successfully detected. • Before detection of free SA, bound SA was released. [ABSTRACT FROM AUTHOR]

Herein, we have synthesized a novel kind of gold nanoclusters decorated iron-cobalt oxide nanosheets (His-AuNCs@FeCo-ONSs) assembled by electrostatic interaction, which possessed both outstanding peroxidase-like activity and fluorescence property. Taking advantage of our bifunctional hybrid nanozyme and enzyme cascade reactions, a sensitive dual-mode (colorimetric/fluorescent) detection method for α-glucosidase was constructed. The detection limits for α-glucosidase were 2.2 U/L and 3.3 U/L in fluorometric and colorimetric mode, respectively. This method not only provides high sensitivity, but also can correct itself to improve the accuracy of analysis due to the dual-response signals. Furthermore, it was employed for α-glucosidase determination in real samples and screening of α-glucosidase inhibitors. The mechanism diagram of dual-mode (colorimetric/fluorescent) detection for α-glucosidase based on a nanozyme-enzymes cascade reaction comprised of α-glucosidase, glucose oxidase and hybrid nanozyme His-AuNCs@FeCo-ONSs. α-Glucosidase activity could be detected by recording the absorbance of generated oxTMB at 652 nm or the fluorescence at 487 nm of His-AuNCs@FeCo-ONSs. [Display omitted] • A hybrid nanozyme His-AuNCs@FeCo-ONSs was firstly prepared. • His-AuNCs@FeCo-ONSs had both enhanced peroxidase-like activity and fluorescence properties. • A dual-mode (colorimetric/fluorescent) detection method for α-glucosidase was developed. • This method was successfully applied in α-glucosidase inhibitors screening. • Enzyme cascade reactions based sensing strategy amplified detection signal. [ABSTRACT FROM AUTHOR]

Enzymes are biological catalysts that facilitate a diverse range of biochemical reactions in a highly specific and efficient manner. The development of inhibitors of several clinically relevant enzymes including acetylcholinesterase, tyrosinase, xanthine oxidase, alkaline phosphatase, and glucosidase has emerged as a promising approach to treating several diseases. The unintentional intake of pesticides or other toxic compounds can also reversibly or irreversibly inhibit the activity of certain enzymes, damaging normal physiological activity in affected individuals. There is thus a critical need to design reliable approaches to detecting the presence of enzymatic inhibitors in a range of sample matrices. Electrochemical biosensors have emerged as promising tools that have been widely employed in the development and detection of enzymatic inhibitors owing to their low-cost, highly efficient, and extremely sensitive characteristics. The present review provides a comprehensive overview of the current status of enzyme inhibition-based electrochemical biosensors. After an initial discussion of different types of inhibition and immobilization strategies employed in the design of these biosensors, the current progress of research efforts focused on the design of enzyme-based electrochemical biosensors aimed at detecting enzymatic inhibitors in the context of both drug development and environmental pollution is discussed. Lastly, this article closes with an overview of current challenges and future development trends associated with electrochemical biosensor fabrication efforts. Together, this review will provide a robust foundation for future research and development work focused on creating novel electrochemical biosensors for use in related fields. [Display omitted] • Different types of enzyme inhibition and immobilization strategies are discussed. • Latest enzyme inhibition-based electrochemical biosensors for pharmaceutical and environmental analysis are reviewed. • Challenges and perspectives of these biosensors are explored. • This review will give inspirations for innovative design of enzyme biosensors. [ABSTRACT FROM AUTHOR]

Diabetes is a highly prevalent and chronic metabolic disease, and the continuous monitoring of diabetes is of great importance for diabetes management. Interstitial fluid glucose has an excellent correlation with blood glucose, and therefore transdermal glucose biosensors can provide accurate monitoring of diabetes. The ongoing challenges are the synergetic integration of biosensing principles, device configuration, signal transduction, novel materials, and fabrication methods. In recent years, there have been several attempts for developing new -transdermal glucose biosensors. To successfully construct a transdermal glucose biosensor, there are several interesting questions: What is the sensing principle for diabetes monitoring? What device configuration should be used? What kinds of materials should be chosen and how to integrate them into one device? What are the application and commercial status? This review would attempt to address the above questions, and explore the fundamental aspects and the practical applications of a variety of transdermal glucose biosensors. It is anticipated that this review could open up exciting opportunities for the development of next-generation transdermal devices, as well as providing monitoring methods for diabetes patients. [Display omitted] • The work reviews the sensing mechanisms for subcutaneous glucose biosensors. • The work reviews the sensing materials, device configurations, and fabrication methods comprehensively. • The work reviews the commercial devices and the application status for subcutaneous glucose biosensors. [ABSTRACT FROM AUTHOR]

Upon near-infrared excitation Tm 3+ +Yb 3+ doped fluorohafnate glasses present upconversion properties and emit visible light. This property permits to use these glasses (UCG) as excitation sources for fluorescent optical biosensors. Taking this into account, in this work a fluorescent biosensor for glucose determination is designed and evaluated. The biosensor combines the UCG and the fluorescence of the enzyme glucose oxidase chemically modified with a fluorescein derivative (GOx-FS), whose intensity is modified during the enzymatic reaction with glucose. Optical parameters have been optimized and a mathematical model describing the behavior of the analytical signal is suggested. Working in FIA mode, the biosensor responds to glucose concentrations up to, at least, 15 mM with a limit of detection of 1.9 mM. The biosensor has a minimum lifetime of 9 days and has been applied to glucose determination in drinks. The applicability of the sensor was tested by glucose determination in two fruit juices. [ABSTRACT FROM AUTHOR]

The ultrasensitive monitoring of glucose with a fast and accurate method is significant in potential therapeutics and optimizes protein biosynthesis. Incorporation of enzyme into matrix is considered as promising candidates for constructing highly sensitive glucose-responsive systems. In this study, three-dimensional poly(acrylic acid) brushes-nanospherical silica (PAA-nano silica) with high amplification capability and stability were used to covalently immobilize bienzymes for cascade enzymatic catalysis. The major advantages of PAA-nano silica-bienzyme co-incorporation is that the enzymes are proximity distribution, and such close confinement both minimized the diffusion of intermediates among the enzymes in the consecutive reaction and improve the utilization efficiency of enzymes, thereby enhancing the overall reaction efficiency and specificity. Thus, this present bienzymatic biosensor shows robust signal amplification and ultrasensitivity of glucose-responsive properties with a detection limit of 0.04 μM. [ABSTRACT FROM AUTHOR]

A series of glucose bioelectrodes were prepared by glucose oxidase (GOx) immobilization into laponite hydrogel films containing DNA bioinspired polycations made of vinylbenzyl thymine (VBT) and vinylbenzyl triethylammonium chloride (VBA) with general formulae [ ( VBT ) m ( VBA ) n ] ≈ 25 n + with m =0, 1 and n =2, 4, 8, deposited onto glassy carbon electrode. The bioelectrodes were characterized by chronoamperometry, cyclic voltammetry and electrochemical impedance spectroscopy. Results indicated that the electrochemical properties of the laponite hydrogel films were largely improved by the incorporation of thymine-based polycations, being proportional to the positive charge density of the polycation molecule. After incorporation of glucose oxidase, the sensitivity of the bioelectrode to glucose increased with the positive charge density of the polycation. Additionally, the presence of the vinylbenzyl thymine moiety played a role in the long-term stability and reproducibility of the bioelectrode signal. As a consequence, the [ ( VBT ) ( VBA ) 8 ] ≈ 25 8 + was the most appropriate polycation for bioelectrode preparation and glucose sensing, with a specific sensitivity of s e =176 mA mmol −1 L cm −2 U −1 , almost two-order of magnitude larger than other laponite immobilized GOx bioelectrodes reported elsewhere. These features were confirmed by testing the bioelectrode for a selective determination of glucose in powder milk and blood serum samples without interference of either ascorbic or uric acids under the experimental conditions. The present study demonstrates the suitability of DNA bioinspired water-soluble polycations [ ( VBT ) m ( VBA ) n ] ≈ 25 n + for enzyme immobilization like GOx into laponite hydrogels, and the preparation of highly sensitive and stable bioelectrodes on glassy carbon surface. [ABSTRACT FROM AUTHOR]

In the line of the applicability of biocompatible monomers pH and temperature dependent, we assayed poly-methacrylic acid (p-MAA) microparticles as immobilization system in the design of enzymatic biosensors. Glucose oxidase was used as enzyme model for the study of microparticles as immobilization matrices and as biological material in the performance of glucose biosensors. The enzyme immobilization method was optimized by investigating the influence of monomer concentration and cross-linker content (N′,N′-methylenebisacrylamide), used in the preparation of the microparticles in the response of the biosensors. The kinetics of the polymerization and the effects of the temperature were studied, also the conversion of the polymerization was determinates by a weight method. The structure of the obtained p-MAA microparticles were studied through scanning electron microscopy (SEM) and differential scanning microscopy (DSC). The particle size measurements were performed with a Galai-Cis 1 particle analyzer system. Furthermore, the influence of the swelling behavior of hydrogel matrix as a function of pH and temperature were studied. Analytical properties such as sensitivity, linear range, response time and detection limit were studied for the glucose biosensors. The sensitivity for glucose detection obtained with poly-methacrylic acid (p-MAA) microparticles was 11.98 mA M −1 cm −2 and 10 μM of detection limit. A Nafion® layer was used to eliminate common interferents of the human serum such as uric and ascorbic acids. The biosensors were used to determine glucose in human serum samples with satisfactory results. When stored in a frozen phosphate buffer solution (pH 6.0) at −4 °C, the useful lifetime of all biosensors was at least 550 days. [ABSTRACT FROM AUTHOR]

A novel amperometric glucose biosensor was proposed in flow injection analysis (FIA) system using glucose oxidase (GOD) and Quantum dot (ZnS–CdS) modified Pencil Graphite Electrode (PGE). After ZnS–CdS film was electrochemically deposited onto PGE surface, GOD was immobilized on the surface of ZnS–CdS/PGE through crosslinking with chitosan (CT). A pair of well-defined reversible redox peak of GOD was observed at GOD/CT/ZnS–CdS/PGE based on enzyme electrode by direct electron transfer between the protein and electrode. Further, obtained GOD/CT/ZnS–CdS/PGE offers a disposable, low cost, selective and sensitive electrochemical biosensing of glucose in FIA system based on the decrease of the electrocatalytic response of the reduced form of GOD to dissolved oxygen. Under optimum conditions (flow rate, 1.3 mL min −1 ; transmission tubing length, 10 cm; injection volume, 100 μL; and constant applied potential, −500 mV vs. Ag/AgCl), the proposed method displayed a linear response to glucose in the range of 0.01–1.0 mM with detection limit of 3.0 µM. The results obtained from this study would provide the basis for further development of the biosensing using PGE based FIA systems. [ABSTRACT FROM AUTHOR]

Creatine kinase (CK: adenosine-5-triphosphate–creatine phosphotransferase) is an important enzyme of muscle cells; the presence of a large amount of the enzyme in blood serum is a biomarker of muscular injuries, such as acute myocardial infarction. This work describes a bi-enzyme (glucose oxidase and hexokinase based) biosensor for rapid and convenient determination of CK activity by measuring the rate of ATP production by this enzyme. Simultaneously the biosensor determines glucose concentration in the sample. Platinum disk electrodes were used as amperometric transducers. Glucose oxidase and hexokinase were co-immobilized via cross-linking with BSA by glutaraldehyde and served as a biorecognition element of the biosensor. The biosensor work at different concentrations of CK substrates (ADP and creatine phosphate) was investigated; optimal concentration of ADP was 1 mM, and creatine phosphate – 10 mM. The reproducibility of the biosensor responses to glucose, ATP and CK during a day was tested (relative standard deviation of 15 responses to glucose was 2%, to ATP – 6%, to CK – 7–18% depending on concentration of the CK). Total time of CK analysis was 10 min. The measurements of creatine kinase in blood serum samples were carried out (at 20-fold sample dilution). Twentyfold dilution of serum samples was chosen as optimal for CK determination. The biosensor could distinguish healthy and ill people and evaluate the level of CK increase. Thus, the biosensor can be used as a test-system for CK analysis in blood serum or serve as a component of multibiosensors for determination of important blood substances. Determination of activity of other kinases by the developed biosensor is also possible for research purposes. [ABSTRACT FROM AUTHOR]

An amperometric biosensor based on chemisorption of glucose oxidase (GOx) on Au seeds decorated on magnetic core Fe 3 O 4 nanoparticles (Fe 3 O 4 @Au) and their immobilization on screen-printed carbon electrode bulk-modified with manganese oxide (SPCE{MnO 2 }) was designed for the determination of glucose. The Fe 3 O 4 @Au/GOx modified SPCE{MnO 2 } was used in a flow-injection analysis (FIA) arrangement. The experimental conditions were investigated in amperometric mode with the following optimized parameters: flow rate 1.7 mL min −1 , applied potential +0.38 V, phosphate buffer solution (PBS; 0.1 mol L − 1 , pH 7.0) as carrier and 3.89 unit mm −2 enzyme glucose oxidase loading on the active surface of the SPCE. The designed biosensor in FIA arrangement yielded a linear dynamic range for glucose from 0.2 to 9.0 mmol L −1 with a sensitivity of 2.52 µA mM −1 cm −2 , a detection limit of 0.1 mmol L −1 and a quantification limit of 0.3 mmol L −1 . Moreover, a good repeatability of 2.8% (number of measurements n =10) and a sufficient reproducibility of 4.0% (number of sensors n =3) were achieved. It was found that the studied system Fe 3 O 4 @Au facilitated not only a simpler enzyme immobilization but also provided wider linear range. The practical application of the proposed biosensor for FIA quantification of glucose was tested in glucose sirup samples, honeys and energy drinks with the results in good accordance with those obtained by an optical glucose meter and with the contents declared by the producers. [ABSTRACT FROM AUTHOR]

An amperometric glucose biosensor based on direct electron transfer of glucose oxidase (GOD) self-assembled on the surface of partially unzipped carbon nanotubes (PUCNTs) modified glassy carbon electrode (GCE) has been successfully fabricated. PUCNTs were synthesized via a facile chemical oxidative etching CNTs and used as a novel immobilization matrix for GOD. The cyclic voltammetric result of the PUCNT/GOD/GCE showed a pair of well-defined and quasi-reversible redox peaks with a formal potential of −0.470 V and a peak to peak separation of 37 mV, revealing that the fast direct electron transfer between GOD and the electrode has been achieved. It is notable that the glucose determination has been achieved in mediator-free condition. The developed biosensor displayed satisfactory analytical performance toward glucose including high sensitivity (19.50 μA mM −1 cm −2 ), low apparent Michaelis–Menten (5.09 mM), a wide linear range of 0–17 mM, and also preventing the interference from ascorbic acid, uric acid and dopamine usually coexisting with glucose in human blood. In addition, the biosensor acquired excellent storage stabilities. This facile, fast, environment-friendly and economical preparation strategy of PUCNT–GOD may provide a new platform for the fabrication of biocompatible glucose biosensors and other types of biosensors. [ABSTRACT FROM AUTHOR]

A method, based on the inhibition of an ultrathin polypyrrole–glucose oxidase (PPy–GOx) potentiometric biosensor response, is described for the detection of Cu 2+ , Hg 2+ , Cd 2+ and Pb 2+ ions. Based on experimental conditions (0.2 M pyrrole, 500 U mL −1 GOx, and an applied current density of 0.05 mA cm −2 and a polymerization period of 500 s) previously published by us, PPy–GOx films of approximately 55 nm thick were used to demonstrate the inhibitive potentiometric detection of selected trace metals down to 0.079 μM Cu 2+ , 0.025 μM Hg 2+ , 0.024 μM Pb 2+ and 0.044 μM Cd 2+ . Furthermore, good linear concentration ranges were achieved for Cu 2+ (0.079–16 μM), Hg 2+ (0.025–5 μM), Pb 2+ (0.10–15 μM) and Cd 2+ (0.04–62 μM). The analysis of the nature of the inhibition of glucose oxidase in the PPy–GOx biosensor by these metals was achieved by Dixon and Cornish-Bowden plots. The shapes of the curves (exponential decay, parabolic and linear) obtained for the inhibitors suggest that the inhibition by the metal ions may not be exclusively directed at the essential –SH group, but involve additional binding sites of the enzyme. Dixon and Cornish-Bowden plots suggest that the inhibition is competitive for Cd 2+ , while non-competitive inhibition was observed for other metal ions. The ultra-thin PPy–GOx film enabled improved permeability to the metal inhibitors than possible with conventional biosensors with thicker films and, hence, better reflects the actual inhibition effect of the trace metals on the enzyme activity. The use of the ultra-thin film also eliminated the usual need for incubation of the enzyme electrode for a long period in the presence of the inhibitors. Furthermore, a rapid recovery of the enzyme activity was achieved by simply washing the electrode with water and storing in phosphate buffer for 10–15 min. The proposed biosensing approach was successfully used for the detection of individual trace metals in tap water, achieving a 98–101% recovery. [ABSTRACT FROM AUTHOR]

A sandwich-type luminol electrochemiluminescence (ECL) aptasensor for highly sensitive and selective detection of platelet-derived growth factor BB (PDGF-BB) is fabricated. For this proposed ECL aptasensor, a multilayered AuNPs-electrochemically reduced graphene (AuNPs-EG) nanocomposite film was formed on the GCE surface as the base of the aptasensor through a co-electrodeposition method. The AuNPs-EG composites possess high conductivity to promote the electron transfer at the electrode interface and good biocompatibility and large surface area to capture large amounts of primary aptamer (Apt1), thus amplifying the detection response. Moreover, glucose oxidase (GOD) functionalized AuNPs labeled secondary aptamer (GOD–Apt2–AuNPs) was designed as the signal probe for the sandwiched aptasensor. Enhanced sensitivity was obtained by in situ generation of H 2 O 2 from reaction between GOD and glucose and the excellent catalytic behavior of AuNPs to the ECL of the luminol–H 2 O 2 system. Under the optimal conditions, the as-prepared ECL aptasensor exhibited excellent analytical property for the detection of PDGF-BB in the range from 1.0×10 –13 to 5.0×10 −10 mol L −1 with a detection limit of 1.7×10 –14 mol L −1 ( S / N =3). The application of the present protocol was demonstrated by analyzing PDGF-BB in human serum and human urine samples with the recoveries from 85.0% to 110%. [ABSTRACT FROM AUTHOR]

Well-distributed hollow gold nanospheres (Aushell@GOD) (20±5 nm) were synthesized using the glucose oxidase (GOD) cross-linked with glutaraldehyde as a template. A glucose biosensor was prepared based on Aushell@GOD nanospheres for catalyzing luminol electrogenerated chemiluminescence (ECL). Firstly, chitosan was modified in a glassy carbon electrode which offered an interface of abundant amino-groups to assemble Aushell@GOD nanospheres. Then, glucose oxidase was adsorbed on the surface of Aushell@GOD nanospheres via binding interactions between Aushell and amino groups of GOD to construct a glucose biosensor. The Aushell@GOD nanospheres were investigated with TEM and UV-vis. The ECL behaviors of the biosensor were also investigated. Results showed that, the obtained Aushell@GOD nanospheres exhibited excellent catalytic effect towards the ECL of luminol-H2O2 system. The response of the prepared biosensor to glucose was linear with the glucose concentration in the range of 1.0 μM to 4.3 mM (R=0.9923) with a detection limit of 0.3 μM (signal to noise=3). This ECL biosensor exhibited short response time and excellent stability for glucose. At the same time the prepared ECL biosensor showed good reproducibility, sensitivity and selectivity. [ABSTRACT FROM AUTHOR]

It is generally accepted that glucose oxidase (GOx) shows unique specificity in β- d -glucose catalysis. However, it has been found that GOx can catalyze diverse monosaccharides. Therefore, the sensing accuracy for glucose biosensors using GOx as probes will be largely compromised by the presence of other monosaccharides. Herein, multifunctional bi-nanospheres (Fe 3 O 4 @Au NCs), which show both peroxidase-like and catalase-like catalytic activities in different working conditions, are successfully constructed and served as desirable platform with huge surface area for the immobilization of large amount of GOx probes. In acidic environment, hydroxyl radicals could be generated via the cascaded catalysis of β- d -glucose by Fe 3 O 4 @Au-GOx, and then employed to initiate the polymerization of boric acid derivative to prepare molecularly imprinted polymers (MIPs) on the surface of GOx using β- d -glucose as template. Then, the molecularly imprinted GOx are immobilized on the surface of highly oriented pyrolytic graphite (HOPG) electrode and an electrochemical biosensor (Fe 3 O 4 @Au-GOx-HOPG) for glucose sensing is successfully obtained. Interestingly, the as-prepared biosensors could selectively detect glucose in the range of 10.0 μM - 5.0 mM with a LOD = 5.0 μM with the help of MIPs, which is comparable or better than other glucose sensors reported recently. The self-protected molecularly imprinted sensing platform is prepared based on the bifunctional bionic enzymes (Fe 3 O 4 @Au NCs) and GOx, which can achieve highly specific and sensitive detection of β- d -glucose among its isomers. [Display omitted] • GOx is lack of specific catalytic capacity among different monosaccharides. • Fe 3 O 4 @AuNCs with both peroxidase-like and catalase-like activities are prepared. • Molecular imprinting is achieved on glucose oxidase via a cascade reaction. • The biosensor shows good sensitivity for β- d -glucose detection among its isomers. • The sensing platform shows enhanced stability due to the introduction of MIPs. [ABSTRACT FROM AUTHOR]

Abstract: A highly-sensitive glucose biosensor amenable to ultra-miniaturisation was fabricated by immobilisation of glucose oxidase (GOx), onto a poly(2,6-diaminopyridine)/multi-walled carbon nanotube/glassy carbon electrode (poly(2,6-DP)/MWNT/GCE). Cyclic voltammetry was used for both the electrochemical synthesis of poly-(2,6-DP) on the surface of a MWNT-modified GC electrode, and characterisation of the polymers deposited on the GC electrode. The synergistic effect of the high active surface area of both the conducting polymer, i.e., poly-(2,6-DP) and MWNT gave rise to a remarkable improvement in the electrocatalytic properties of the biosensor. The transfer coefficient (α), heterogeneous electron transfer rate constant and Michaelis–Menten constant were calculated to be 0.6, 4s−1 and 0.20mM at pH 7.4, respectively. The GOx/poly(2,6-DP)/MWNT/GC bioelectrode exhibited two linear responses to glucose in the concentration ranging from 0.42μM to 8.0mM with a correlation coefficient of 0.95, sensitivity of 52.0μAmM−1 cm−2, repeatability of 1.6% and long-term stability, which could make it a promising bioelectrode for precise detection of glucose in the biological samples. [Copyright &y& Elsevier]

Abstract: A mesoporous silica nanoshpere (MSN) was proposed to modify glassy carbon electrode (GCE) for the immobilization of protein. Using glucose oxidase (GOD) as a model, direct electrochemistry of protein and biosensing at the MSN modified GCE was studied for the first time. The MNS had large surface area and offered a favorable microenvironment for facilitating the direct electron transfer between enzyme and electrode surface. Scanning electron microscopy, transmission electron microscopy, UV–vis spectroscopy and cyclic voltammetry were used to examine the interaction between GOD and the MSN matrix. The results demonstrated that the immobilized enzyme on the MSN retained its native structure and bioactivity. In addition, the electrochemical reaction showed a surface controlled, reversible two-proton and two-electron transfer process with the apparent electron transfer rate constant of 3.96s−1. The MNS-based glucose biosensor exhibited the two linear ranges of 0.04–2.0mM and 2.0–4.8mM, a high sensitivity of 14.5mAM−1 cm−2 and a low detection limit of 0.02mM at signal-to-noise of 3. The proposed biosensor showed excellent selectivity, good reproducibility, acceptable stability and could be successfully applied in the reagentless detection of glucose in real samples at −0.45V. The work displayed that mesoporous silica nanosphere provided a promising approach for immobilizing proteins and fabrication of excellent biosensors. [Copyright &y& Elsevier]

Abstract: Fabrication of an enzyme amperometric biosensor for glucose via electropolymerization of pyrrole in the presence of glucose oxidase onto a hydrogel coated platinum electrode is hereby established as a viable biotransducer fabrication method. Platinum micro- (ϕ=25μm) and macro- (ϕ=100μm) electrodes were electrochemically activated and chemically modified with 3-aminopropyl-trimethoxysilane (APTMS), functionalized with acryloyl(polyethyleneglycol)-N-hydroxysuccinamide (ACRL-PEG-NHS), dipped into a polyHEMA based hydrogel cocktail and UV cross-linked. Electropolymerization of Py in the presence of GOx produced glucose responsive biotransducers that showed; (i) a 4-fold reduction in sensitivity compared with directly electropolymerized PPy films, (ii) an electropolymerization charge density dependence of biotransducer sensitivity and enzyme activity that was maximal at 1.0mC/cm2 with an apparent K M of 33mM, (iii) interference screening of ascorbic acid and (iv) a temporal increase in sensitivity with storage over a 17 days period. This method has the ability to precisely and quantitatively add enzyme catalytic bioactivity to metal or semiconductor biointerfaces for applications in biosensors, bioelectronics and bionics. [Copyright &y& Elsevier]

Abstract: A mediatorless glucose biosensor was developed by the immobilization of glucose oxidase (GOx) to graphene-functionalized glassy carbon electrode (GCE). The surface of GCE was functionalized with graphene by incubating it with graphene dispersed in 3-aminopropyltriethoxysilane (APTES), which acted both as a dispersion agent for graphene and as an amine surface modification agent for GCE and graphene. This was followed by the covalent binding of GOx to graphene-functionalized GCE using 1-ethyl-3-[3-dimethylaminopropyl]carbodiimide hydrochloride (EDC) based crosslinking. Graphene provided signal enhancement by providing greater surface area for GOx binding, while APTES-functionalization led to a higher GOx immobilization density by providing free amino groups for crosslinking. The developed biosensor used a redox potential of −0.45V (vs. Ag/AgCl) for detecting glucose in the diabetic pathophysiological range 0.5–32mM. There was no interference from endogenous electroactive substances and drug metabolites. The developed biosensor was further validated for detecting blood glucose in commercial artificial blood glucose linearity standards in the range 1.4–27.9mM. Therefore, it is ideal for diabetic blood glucose monitoring. The developed bioanalytical procedure for preparation of GOx-bound graphene-functionalized GCEs had high production reproducibility and high storage stability, which is appropriate for the commercial mass production of enzyme-bound electrodes. [Copyright &y& Elsevier]

Abstract: A glucose biosensor was fabricated based on electrostatic self-assembly in combination with in situ photo-cross-linking of glucose oxidase (GOx) and diazoresin–chitosan (DAR–CS) on Prussian blue deposited multi-walled carbon nanotubes (PB-MWNTs) backbone. It was demonstrated that GOx was initially ionically deposited and subsequently covalently photo-cross-linked onto the PB-MWNTs backbone using photosensitive DAR–CS as the assembly interlayer. The modified electrode exhibited good electrical conductivity and effective electron transfer mediation toward H2O2 reduction due to the employment of PB-MWNTs as the fabrication backbone. The biosensor showed high sensitivity of 77.9μAmM−1 cm−2 to glucose in the linear concentration range from 1.0×10−5 to 1.1×10−3 M with fast response time of 10s, detection limit of 3.1×10−6 M, and good anti-interference ability. More importantly, the biosensor exhibited greatly improved biosensing stability in comparison with the non-photo-cross-linked biosensor attributed to the conversion of weak ionic bonds to strong covalent ones for enzyme immobilization by the proposed strategy. The results for glucose determination in real serum samples with the biosensor were found to be in good agreement with those obtained by the conventional clinical procedure. [Copyright &y& Elsevier]

Abstract: A novel glucose biosensor based on the chemiluminescence (CL) detection of enzymatically generated H2O2 was constructed by the effective immobilization of glucose oxidase (GOD)/carbon-nanotubes (CNTs)/gold nanoparticles (GNPs) in nafion film on graphite support. The influences of various experimental parameters such as solution pH, the action time of the enzyme, interferents and the concentration of CL reagents were investigated. Carbon nanotubes and gold nanoparticles offer excellent catalytic activity toward hydrogen peroxide generation in enzymatic reaction between glucose oxidase and glucose, which would enable sensitive determination of glucose. Under the optimum condition, the linear response range of glucose was found to be 2.25×10−6 to 1.75×10−4 molL−1, and the detection limit (defined as the concentration that could be detected at the signal-to-noise ratio of 3) was 1.00×10−6 molL−1. The CL biosensor exhibited good storage stability, i.e., 80% of its initial response was retained after 10 days storage at pH 7.0. The present CL biosensor has been used to determine the glucose concentrations in real serum and urine samples with satisfactory results. [Copyright &y& Elsevier]

Abstract: A new glucose amperometric biosensor, based on electrodeposition of platinum nanoparticles onto the surface of multi-wall carbon nanotube (MWNT)-polyaniline (PANI) nanocomposites, and then immobilizing glucose oxidase (GOD) with covalent interaction and adsorption effect, was constructed in this paper. Firstly, the MWNT-PANI nanocomposites had been synthesized by in situ polymerization and were characterized through transmission electron microscopy (TEM), Fourier transform infrared (FT-IR) spectroscopy, and ultraviolet and visible (UV–vis) absorption spectra. The assembled process of the modified electrode was probed by scanning electron microscopy (SEM) and cyclic voltammetry (CV). Chronoamperometry was used to study the electrochemical performance of the resulting biosensor. The glucose biosensor exhibited a linear calibration curve over the range from 3.0μM to 8.2mM, with a detection limit of 1.0μM and a high sensitivity of 16.1μAmM−1. The biosensor also showed a short response time (within 5s). Furthermore, the reproducibility, stability and interferences of the biosensor were also investigated. [Copyright &y& Elsevier]

Abstract: A strategy of protein-entrapment in bicontinuous gyroidal mesoporous carbon (BGMC) nanocomposite films is described. Herein, the quasi-reversible electron transfer of redox proteins (such as glucose oxidase and myoglobin) is probed and the associated biocatalytic activity is revealed. The apparent heterogeneous electron transfer rate constant of the immobilized glucose oxidase is up to 9.4s−1, much larger than those in carbon nanotubes and some conventional mesoporous carbons. The BGMC based glucose biosensor enables the determination of glucose at a potential of 0.6V (vs. SCE). Its detection limit is 1.0×10−5 M (signal-to-noise ratio, S/N=3), the linear response is up to 7.49mM and the detection sensitivity is 52.5nAmM−1 Furthermore, a series of BGMCs with different pore sizes is designed and synthesized using sucrose or phenol formaldehyde resin to study the influences of pore sizes and carbon sources on the immobilization of redox proteins and on the heterogeneous electron transfer. [ABSTRACT FROM AUTHOR]

Abstract: Ordered mesoporous carbon–Au nanoparticles (OMC–Au) nanocomposites were synthesized by a one-step chemical reduction route. Due to the large surface area and high conductivity of OMC, good biocompatibility of OMC and Au nanoparticles, a mediator-free glucose biosensor was fabricated by immobilizing glucose oxidase (GOD) on the OMC–Au nanocomposites modified glassy carbon (GC) electrode. Direct electron transfer between GOD and the electrode was achieved and the electron transfer rate constant (k s ) was calculated to be 5.03s−1. The Michalis–Menten constant value of GOD immobilized on the OMC–Au/GC electrode surface was found to be 0.6mM. The glucose biosensor exhibits a linear range from 0.05 to 20.0mM. This biosensor also shows good reproducibility, excellent stability and the negligible interferences from ascorbic acid and uric acid. [ABSTRACT FROM AUTHOR]

Abstract: Optical biosensor arrays for rapidly determining the glucose concentrations in a large number of beverage and blood samples were developed by immobilizing glucose oxidase (GOD) on oxygen sensor layer. Glucose oxidase was first encapsulated in silica based gels through sol–gel approach and then immobilized on 96-well microarrays integrated with oxygen sensing film at the bottom. The oxygen sensing film was made of an organically modified silica film (ORMOSIL) doped with tris(4,7-diphenyl-1,10-phenanthroline) ruthenium dichloride (Ru(dpp)3Cl2). The oxidation reaction of glucose by glucose oxidase could be monitored through fluorescence intensity enhancement due to the oxygen consumption in the reaction. The luminescence changing rate evaluated by the dynamic transient method (DTM) was correlated with the glucose concentration with the wide linear range from 0.1 to 5.0mM (Y =13.28X −0.128, R =0.9968) and low detection limit (0.06mM). The effects of pH and coexisting ions were systemically studied. The results showed that the optical biosensor arrays worked under a wide range of pH value, and normal interfering species such as Na+, K+, Cl−, PO4 3−, and ascorbic acid did not cause apparent interference on the measurement. The activity of glucose oxidase was mostly retained even after 2-month storage, indicating their long-term stability. [ABSTRACT FROM AUTHOR]

Abstract: A new glucose biosensor had been developed by immobilizing positively charged gold nanoparticles (PGNs) on organosilica nanosphere functionalized prussian blue (OSiFPB)-modified gold electrode. The OSiFPB compound could not only effectively prevent the leakage of the PB mediator during measurements, but also easily form stable film on the electrode surface with efficient redox-activity and excellent conductivity. Furthermore, with the negatively charged surface of OSiFPB, this film could be used as an interface to adsorb the PGNs, which provided a congenial microenvironment for adsorbing biomolecules and decreased the electron-transfer impedance. So, with glucose oxidase as a model biomolecular, the proposed sensor showed rapid and highly sensitive amperometric response to glucose and this immobilization approach effectively improved the stability of the electron-transfer mediator. This work would be promising for construction of biosensor and bioelectronic devices. [Copyright &y& Elsevier]

Abstract: A novel enzyme reactor with co-immobilization of β-galactosidase and glucose oxidase in calcium alginate fiber (CAF) and amine modified nanosized mesoporous silica (AMNMS) was prepared which incorporate the adsorption and catalysis of AMNMS with the cage effect of the polymer to increase catalytic activity and stability of immobilized enzyme. The enzyme reactor was applied to prepare a chemiluminescence (CL) flow-through biosensor for determination of lactose combined with a novel luminol-diperiodatonickelate (DPN) CL system we reported. It shows that the CL flow-through biosensor possesses long lifetime, high stability, high catalytic activity and sensitivity. The relative CL intensity was linear with the lactose concentration in the range of 8×10−8–4×10−6 gmL−1 with the detection limit of 2.7×10−8 gmL−1 (3σ). It has been successfully applied to the determination of lactose in milk. [Copyright &y& Elsevier]

Abstract: Glucose oxidase (GOx) has been immobilized within poly(dimethylamino) ethyl methacrylate (p-DMAEM) microparticles which were subsequently used as biological material in the fabrication of a glucose biosensor. The enzyme immobilization method was optimized in relation with the monomer concentration and cross-linker content. It was found that the best biosensor response corresponds to microparticles synthesized with 1.19M monomer and 0.37% cross-linking content. Furthermore, the influence on the biosensor response of parameters such as working potential, pH, temperature, and loaded enzyme were investigated. In addition, analytical properties such as sensitivity, linear range, response time, and detection limit were determined. The biosensor was used to analyze glucose in human serum samples with satisfactory results. The useful lifetime of the biosensor is at least 520 days. [Copyright &y& Elsevier]

Abstract: Polymerized ionic liquid-wrapped carbon nanotubes (PIL-CNTs) were firstly designed for direct electrochemistry and biosensing of redox proteins. The CNTs were coated successfully with polymerized ionic liquid (PIL) layer, as verified by transmission electron microscopy (TEM), thermogravimetric analysis (TGA) and Fourier transform infrared (FT-IR) spectroscopy. The PIL-CNTs were dispersed better in water and showed superior electrocatalysis toward O2 and H2O2 comparing to pristine CNTs and the mixture of IL monomer and CNTs. With glucose oxidase (GOD) as a protein model, the direct electrochemistry of the redox protein was investigated on the PIL-CNTs modified glassy carbon (GC) electrode and excellent direct electrochemical performance of GOD molecules was observed. The proposed biosensor (GOD/PIL-CNTs/GC electrode) displayed good analytical performance for glucose with linear response up to 6mM, response sensitivity of 0.853μAmM−1, good stability and selectivity. [Copyright &y& Elsevier]

Abstract: The design and characterization of a new organic–inorganic hybrid composite material for glucose electrochemical sensing are described. This material is based on the entrapment of both gold nanoparticles (AuNPs) and glucose oxidase, which was chosen as a model, into a sol–gel matrix. The addition of spectroscopic grade graphite to this system, which confers conductivity, leads to the development of a material particularly attractive for electrochemical biosensor fabrication. The characterization of the hybrid composite material was performed using atomic force microscopy and scanning electron microscopy techniques. This composite material was applied to the determination of glucose in presence of hydroxymethylferrocene as a redox mediator. The system exhibits a clear electrocatalytic activity towards glucose, allowing its determination at 250mV vs Ag/AgCl. The performance of the resulting enzyme biosensor was evaluated in terms of sensitivity, detection limit, linear response range, stability and accuracy. Finally, the enhancement of the analytical response of the resulting biosensor induced by the presence of gold nanoparticles was evaluated by comparison with a similar organic–inorganic hybrid composite material without AuNPs. [Copyright &y& Elsevier]

Abstract: A strategy of protein entrapment within mesoporous carbon matrices is demonstrated to probe the electrochemistry of glucose oxidase. Large surface area and remarkable electro-catalytic properties of carbon mesoporous materials make them suitable candidates for high loading of protein molecules and the promotion of heterogeneous electron transfer. In this work, two kinds of mesoporous carbon nanocomposite films were designed and prepared with highly ordered two-dimensional (2D) and three-dimensional (3D) structures for the immobilization of glucose oxidase, in which the quasi-reversible electron transfer of the redox enzyme was probed, and the apparent heterogeneous electron transfer rate constants () are 3.9 and 4.2s−1, respectively. Furthermore, the associated biocatalytic activity was also revealed. Highly ordered 3D-mesoporous carbon material exhibited larger adsorption capacity for glucose oxidase and the immobilized enzymes retained a higher bioactivity compared with 2D-mesoporous carbons. The preparation of protein-entrapped mesoporous carbon nanocomposites expands the scope of carbon-based electrochemical devices and opens a new avenue for the development of biosensors. [Copyright &y& Elsevier]

Abstract: Egg shell membrane is a novel, robust, microporous, cost effective, easily available organic support material. In recent studies egg shell membranes were utilized as organic support for enzyme immobilization. But low conjugation yield limits its application as good support for biotechnological industries. In present study egg shell membrane was chemically treated to introduce free functional groups for covalent linkage of proteins to increase its conjugation yield and stability of conjugate complex. Many enzymes were tested for immobilization on modified egg shell membrane like oxalate oxidase, glucose oxidase, peroxidase and lipase. A fifteen to sixteen fold increase in conjugation yield was observed when immobilization was performed after chemical treatment in comparison to immobilization on native membrane with slight change in specific activity of immobilized enzyme which ranges from 5% to 15%. Egg shell membrane bound enzymes showed slight changes in their kinetic properties after immobilization. Egg shell membrane bound oxalate oxidase shows detection limit of 1.5μM when used for urinary oxalate determination. Egg shell membrane support shows no interference to enzyme activity and a good correlation of 0.99 was observed with the values estimated using commercially available Sigma kit. The immobilized oxalate oxidase, glucose oxidase, peroxidase and lipase were stable up to duration of 180 days and there is respective loss of 10%, 13%, 24%, and 33% of initial activity. Overall result strengthens our view of using chemically modified egg shell membrane as solid support for better immobilization of enzymes and can be used in various biotechnological applications. [Copyright &y& Elsevier]

Abstract: Electroactive nanostructured membranes have been produced by the layer-by-layer (LbL) technique, and used to make electrochemical enzyme biosensors for glucose by modification with cobalt hexacyanoferrate redox mediator and immobilisation of glucose oxidase enzyme. Indium tin oxide (ITO) glass electrodes were modified with up to three bilayers of polyamidoamine (PAMAM) dendrimers containing gold nanoparticles and poly(vinylsulfonate) (PVS). The gold nanoparticles were covered with cobalt hexacyanoferrate that functioned as a redox mediator, allowing the modified electrode to be used to detect H2O2, the product of the oxidase enzymatic reaction, at 0.0V vs. SCE. Enzyme was then immobilised by cross-linking with glutaraldehyde. Several parameters for optimisation of the glucose biosensor were investigated, including the number of deposited bilayers, the enzyme immobilisation protocol and the concentrations of immobilised enzyme and of the protein that was crosslinked with PAMAM. The latter was used to provide glucose oxidase with a friendly environment, in order to preserve its bioactivity. The optimised biosensor, with three bilayers, has high sensitivity and operational stability, with a detection limit of 6.1μM and an apparent Michaelis–Menten constant of 0.20mM. It showed good selectivity against interferents and is suitable for glucose measurements in natural samples. [Copyright &y& Elsevier]

Abstract: Doped carbon nanotubes are now extremely attractive and important nanomaterials in bioanalytical applications due to their unique physicochemical properties. In this paper, the boron-doped carbon nanotubes (BCNTs) were used in amperometric biosensors. It has been found that the electrocatalytic activity of the BCNTs modified glassy carbon (GC) electrode toward the oxidation of hydrogen peroxide is much higher than that of the un-doped CNTs modified electrode due to the large amount of edge sites and oxygen-rich groups located at the defective sites induced by boron doping. Glucose oxidase (GOD) was selected as the model enzyme and immobilized on the BCNTs modified glassy carbon electrode by entrapping GOD into poly(o-aminophenol) film. The performance of the sensor was investigated by electrochemical methods. At an optimum potential of +0.60V and pH 7.0, the biosensor exhibits good characteristics, such as high sensitivity (171.2nAmM−1), low detection limit (3.6μM), short response time (within 6s), satisfactory anti-interference ability and good stability. The apparent Michaelis–Menten constant () is 15.19mM. The applicability to the whole blood analysis of the enzyme electrode was also evaluated. [Copyright &y& Elsevier]

Abstract: Poly(ethylene glycol) methyl ether methacrylate (PEGMEM) microparticles were synthesized and glucose oxidase (GOx) was immobilized within the microparticles. An amperometric biosensor was fabricated using the microparticles with GOx as biological component. The enzyme immobilization method was optimized by investigating the influence of monomer concentration and cross-linker content used in the preparation of the microparticles in the response of the biosensor. The best analytical results were obtained with the microparticles prepared with 0.21M PEGMEM and 0.74% cross-linking. Furthermore, we have investigated the influence on the biosensor behaviour of parameters such as working potential, pH, temperature and enzymatic load. In addition, analytical properties such as sensitivity, linear range, response time and detection limit were determined. The biosensor was used to determine glucose in human serum samples and to avoid common interferents present in human serum such as uric and ascorbic acids. A Nafion layer was deposited on the electrode surface with satisfactory results. The useful lifetime of the biosensor was at least 520 days. [Copyright &y& Elsevier]