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A chemiluminescence (CL) sensor was constructed for the one-step determination of glucose. Glucose oxidase (GOx) was successfully encapsulated into Zn-doped zeolitic imidazolate framework-67 (Zn–ZIF–67) via a simple one-pot strategy. The as-prepared GOx@Zn–ZIF–67 nanocomposite can trigger cascade reactions of glucose oxidation to generate H2O2 and H2O2-mediated luminol reaction to give an intense CL emission. The sensor responds linearly to glucose in the 20.0–400.0 μmol·L–1 range with a limit of detection (LOD) of 4.7 μmol·L–1. Eleven replicated measurements of 200.0 μmol·L–1 glucose solution gives a relative standard deviation (RSD) of 1.7%. The sensor exhibits good selectivity and stability and was successfully applied to the determination of glucose in real human serum samples. Schematic representation of one-step determination of serum glucose with GOx@Zn–ZIF–67 nanocomposite triggering cascade reactions between luminol and glucose.

Polyaniline (PANI) was functionalized by thiol-ene click chemistry to obtain carboxylic acid–tethered polyaniline (PCOOH). The versatility of PCOOH as an immobilization matrix was demonstrated by constructing four different biosensors for detection of metabolites and cancer biomarker. Immobilization efficiency of PCOOH was investigated by surface plasmon resonance and fluorescence microscopic analysis which revealed dense immobilization of biomolecules on PCOOH as compared to conventional PANI. A sandwich electrochemical biosensor was constructed using PCOOH for detection of liver cancer biomarker, α-fetoprotein (AFP). The sensor displayed sensitivity of 15.24 µA (ng mL−1)−1 cm−2, with good specificity, reproducibility (RSD 3.4%), wide linear range (0.25–40 ng mL−1) at − 0.1 V (vs. Ag/AgCl), and a low detection limit of 2 pg mL−1. The sensor was validated by estimating AFP in human blood serum samples where the AFP concentrations obtained are consistent with the values estimated using ELISA. Furthermore, utilization of PCOOH for construction of enzymatic biosensor was demonstrated by covalent immobilization of glucose oxidase, uricase, and horseradish peroxidase (HRP) for detection of glucose, uric acid, and H2O2, respectively. The biosensors displayed reasonable sensitivity (50, 148, 127 µA mM−1 cm−2), and linear ranges (0.1–5, 0.1–6, 0.1–7 mM) with a detection limit of 10, 1, and 8 µM for glucose, uric acid, and H2O2, respectively. The present study demonstrates the capability of PCOOH to support and enable oxidation of H2O2 generated by oxidase enzymes as well as HRP enzyme catalyzed reduction of H2O2. Thus, PCOOH offers a great promise as an immobilization matrix for development of high-performance biosensors to quantify a variety of other disease biomarkers. Carboxylic acid–tethered polyaniline synthesized by thiol-ene click chemistry was used as matrix to construct four different electrochemical biosensors for detection of cancer biomarker α-fetoprotein, glucose, uric acid, and H2O2.

A simple and efficient method was used to synthesize norepinephrine-induced AuPd aerogels (AuPd-NE) with dual enzyme properties, i.e. glucose oxidase-like property, and peroxidase-like property. Thus, AuPd-NE aerogels can be considered as a tandem nanozyme with tandem enzyme-like activity. In the presence of AuPd-NE aerogels, glucose can be decomposed into gluconic acid and H2O2. Then, H2O2 will continue to decompose into ·OH and H2O. The generated ·OH will oxidize colorless 3,3′,5,5′-tetramethylbenzidine (TMB) to blue products of ox-TMB. Accordingly, an enzyme-free method based on AuPd-NE aerogels was proposed for sensitive colorimetric detection of glucose. The linear range of the developed method was 30 to 250 μM, and the limit of detection was 10 μM. The method presents reliable applicability for blood glucose detection in human serum samples. This study will deepen the understanding of tandem nanozymes and then rationally design tandem nanozymes for many fascinating biomedical applications. A simple, sensitive and reliable one-pot enzyme-free colourimetric assay for glucose was developed

Using an ultrasonication-assisted liquid exfoliation method, we have synthesized PtS2 nanosheets with good reproducibility. Herein, intrinsic peroxidase-like activity was for the first time demonstrated for PtS2 nanosheets, which can catalyze H2O2 oxidation of 3,3′,5,5′-tetramethylbenzidine (TMB) to generate a colored solution. The catalytic mechanism of PtS2 nanosheets was investigated, which indicated that acceleration of the electron transfer between TMB and H2O2 was the main reason for the peroxidase-like activity of PtS2 nanosheets. Based on these observations, we exploited PtS2 nanosheets integrated into dopamine-functionalized hyaluronic acid (HA-DA) hydrogel microspheres by droplet microfluidics to construct PtS2 nanosheet– and PtS2@HA-DA microsphere–based sensors for highly sensitive determination of H2O2. When coupled with glucose oxidase, we further developed two glucose sensors based on the above two methods. Among them, the linearity of the PtS2 nanosheet–based spectrophotometry was in the range of 0.5 to 150 μM and the limit of detection as low as 0.20 μM. The linearity of the microsphere-based colorimetry was in the range 200 to 12,000 μM with a detection limit of 29.95 μM. Both of the glucose sensors can be applied to the determination of glucose in human serum with reliable results and reproducibility.

Cadmium cobaltite (CdCo2O4) nanosheets were ultra-fast synthesized based on a new basic deep eutectic solvent (DES) which served simultaneously as reactant, solvents, and template. Interestingly, the nanosheets were found to exhibit triple-enzyme mimetic activities including oxidase-like activity, peroxidase-like activity, and catalase-like activity. Their catalytic activity followed the typical Michaelis-Menten kinetics, and high affinity for H2O2 and TMB was observed. Based on the superior peroxidase-like catalytic activity of CdCo2O4 nanosheets, a highly sensitive and selective colorimetric strategy for the determination of glucose was established. Under optimized conditions, the absorbance at 652 nm increases linearly in the 0.5 to 100 μM concentration range, and the limit of detection is 0.13 μM (S/N = 3). Finally, the method was successfully used for determination of glucose in serum samples.

A method is described for modulating the anodic photoelectrochemistry of netlike CdS quantum dots through the deposition and dissolution of the electron acceptor manganese dioxide (MnO2) on the surface of the photoelectrode. Specifically, the photocurrent of a CdS-modified indium tin oxide (ITO/CdS) electrode is inhibited by chemical deposition of MnO2. However, the photocurrent becomes recovered by oxidative removal of MnO2 with H2O2. This deposition-dissolution reaction modulates the photoelectrochemistry of CdS effectively. A bioassay for Escherichia coli (E. coli) O157:H7 is designed that uses the antimicrobial peptide magainin I as the recognition element. Glucose oxidase (GOx) acts as a catalytic label tracer to produce the signaling molecule H2O2 in the microwell plates. The enzymatically generated H2O2 etches the deposited MnO2 on the photoelectrode and thus enhances the photocurrent. This detection scheme does not cause any damage to biomolecules. It also avoids the adverse effects of immobilized biomolecules for retarding signal production and leads to improved detection when compared to conventional PEC configurations. E. coli can be detected in the 10 to 5.0 × 106 CFU·mL−1 concentration range, and the limit of detection is 3 CFU·mL−1.

A metal organic framework obtained from cerium(III) and trimesic acid was pyrolyzed to obtain a novel nanostructure referred to as CeO2/C nanowires. The experimental parameters temperature, precursor and gas atmosphere were optimized. The nanowires show good dispersion and a large number of oxygen vacancies, and this leads to excellent peroxidase-like activity. The nanowires are stable at pH values between 2 and 10, and in the 4–80 °C temperature range. The peroxidase-mimicking activity was exploited in a sensitive colorimetric method for determination of H2O2 by using 3,3′,5,5′-tetramethylbenzidine as the chromogenic substrate. The absorbance at 652 nm increases linearly in the 0.5 to 100 μM H2O2 concentration range. If glucose oxidase is added to a solution containing glucose, H2O2 will be enzymatically produced. This was exploited to design a new method for determination of glucose. The optical response is linear in the 1–100 μM glucose concentration range, and the detection limit is 0.69 μM (at S/N = 3). The method was successfully applied to the determination of glucose in serum samples.

The authors describe a new kind of enzymatic glucose assay. The strategy involves three processes: (a) Generation of H2O2 via glucose oxidase catalyzed oxidation of glucose; (b) production of 2,3-diaminophenazine (DAP) from H2O2 and o-phenylenediamine (OPD) via peroxidase-catalyzed oxidation; and (c) a reduction of the blue fluorescence of SiNPs with emission maxima at 445 nm via an inner filter effect that is caused by DAP which is yellow and has an absorption peak at 450 nm. Fluorescence drops with increasing glucose concentrations in the 0.01 to 7 mM concentration range, and the detection limit is 3.5 μM. The assay was successfully applied to the analysis of glucose in human serum.

The paper describes a colorimetric sandwich enzyme-linked immunosorbent assay (ELISA) for the determination of human IgG. It is based on the use of an Fe(II) coordination complex as a signal amplifier and of mesoporous silica nanoparticles modified with glucose oxidase (GOx) and secondary antibodies (Ab2). After formation of the immuno sandwich complex, the quantity of GOx is proportional to the quantity of IgG. On addition of Fe(II) and glucose, GOx catalyzes the oxidation of glucose to produce hydrogen peroxide which oxidizes Fe(II) to Fe(III). After adding a stop solution containing the complexing ligand 1,10-phenanthroline (Phen), un-reacted Fe(II) forms an orange-red complex with Phen which can be detected by plate reader and even seen with bare eyes. This sandwich ELISA has a linear response in the 1 pg.mL−1 to 100 ng.mL−1 human IgG concentration range and a 860 fg.mL−1 detection limit. This is 20 times lower than the commercial ELISA for human IgG. The assay also is selective, stable, highly sensitive and cost-effective.

A colorimetric assay is described for the determination of H2O2 and glucose based on the peroxidase-mimicking activity of Fe3O4 magnetic nanoparticles functionalized with a poly(ethylene glycol) derivative (PEG-MNPs). PEG ligands conjugated to a phosphine oxide and a phospholipid were synthesized and deposited on the surface of magnetic nanoparticles (MNPs). This leads to enhanced peroxidase-like activity of the MNPs by providing more monodispersed MNPs to be present in solution and by reducing self-aggregation. The PEG-MNPs were then used as enzyme mimetics that catalyze the oxidation of 2,2′-azino-bis(3-ethylbenzo-thiazoline-6-sulfonic acid) to form a green product having an absorption maximum at 417 nm which enables a visual detection of H2O2. These findings are exploited in a highly sensitive and selective glucose bioassay based on the formation of H2O2 by glucose oxidase (GOx). The calibration plot covers the glucose concentration range from 5 μM to 1 mM, and the limit of detection is as low as 3 μM. The diagnostic capability of the method is demonstrated by analyzing glucose in human blood serum. It is perceived that the PEG-MNPs presented here also may act as potent peroxidase mimetics in other methods for the determination of clinically important analytes.

The authors describe enzyme based nanobiosensors for continuous monitoring of glucose, with the long term goal of using them as smart diagnostic tattoos. The method is founded on two main features: (1) The fluorescence intensity and decay times of glucose oxidase (GOx) and of GOx labeled with fluorescein (FS) or a ruthenium chelate (Ru) reversibly change during interaction with glucose; (2) The (labeled) enzyme is linked to magnetite magnetic nanoparticles (MNPs) which permits the MNPs to be physically manipulated. It is found that a stable link between MNPs and GOx is only accomplished if the number of amino groups on the GOX is artificially enlarged (to form GOxsam). Fluorescence decay data are best acquired with 8-nm MNPs where scattering is marginal; The activity of GOx is found not to be affected by immobilization on the MNPs. The various immobilized enzymes (GOxsam, GOxsam-FS and GOxsam-Ru; all on MNPs) differ only slightly in terms of linear response to glucose which ranged from 0.5 mM to at least 3.5 mM. The RSDs are about 5% (for n = 5), the detection limits are at ∼50 μM, and the sensor lifetimes are >1 week.

The authors describe a fluorometric glucose assay that is based on the use of MnO2 nanosheets and copper nanoclusters (CuNCs) acting as nanoprobes. The CuNCs were synthesized by using bovine serum albumin as a template by chemical reduction of copper(II) sulfate. On addition of MnO2 nanosheets to a colloidal solution of CuNCs, the fluorescence of CuNCs (measured at excitation/emission wavelengths of 335/410 nm) is quenched. However, in the presence of enzymatically generated H2O2, the MnO2 nanosheets are reduced to form Mn(II) ions. As a result, fluorescence intensity recovers. The glucose assay is based on the enzymatic conversion of glucose by glucose oxidase to generate H2O2 and glucuronic acid. The calibration plot is linear in the 1 μM to 200 μM glucose concentration range, and the detection limit is 100 nM. The method was successfully applied to the determination of glucose in spiked human serum samples.

We describe a maskless photopolymerization technique for integration of luminescent sensors for determination of pH values and dissolved oxygen (DO) into commercially available all-glass microfluidic reactors (in sizes as small as 43 ± 3 μm for both DO and pH sensors). The sensor spots are poly(ethyleneglycol acrylate)-based and obtained by photopolymerization of oligomers in the presence of optical probes for oxygen and pH values, respectively. The resulting devices were applied to in-line monitoring of enzymatic conversions of acetylcholine and glucose (by using acetylcholine esterase and glucose oxidase, respectively) on the microscale. The detection limits are 258 μM and 505 μM for acetylcholine and glucose, respectively. The method has a large potential in terms of monitoring enzymatic and other chemical reactions on the microscale in that it does not require special instrumentation apart from a standard widefield fluorescence microscope.

A pH-responsive superwettable chip is described whose surface can switch between superhydrophobic and superhydrophilic. It can be used for the visual detection of the prostate specific antigen (PSA) based on contact angle readout. Magnetic beads were modified with primary antibody against PSA. After immunobinding, gold nanoparticles loaded with secondary antibody labeled with glucose oxidase is added. On addition of glucose, gluconic acid is formed which causes a drop in the local pH value. This results in a wettability switch of the pH-responsive superwettable chip from hydrophobic to hydrophilic. Under the optimized conditions, PSA can be quantified with a 3.2 pg mL−1 limit of detection by analyzing the contact angle and the related color that changes from blue via orange to red. The method is applicable to PSA detection in serum samples and for visual classification by cancer patients and healthy persons. It is also suitable for color-blind and color-weak individuals. Conceivably, this kind of assay can be transferred to the determination of various kinds of other bioanalytes including nucleotide, proteins, and even of ions and small organic molecules, and thus is has a wide scope.

A nanostructured catalyst is introduced that demonstrates peroxidase mimicking activity. It consists of nickel- and nitrogen-doped graphene nanotubes loaded with platinum nanoparticles. Pt-decorated Ni-doped nitrogen-rich graphitic nanotube (Pt/Ni@NGT) was synthesized using a two-step procedure in which the precursors were first refluxed to form a supramolecular assembly followed by a pyrolysis and leaching step to form nanotubes. Afterwards, Pt was decorated on the outer surface of nanotube by an ultrasound assisted method. Pt/Ni@NGT was characterized by XPS, TEM, SEM, and HAADF–STEM. The as-prepared Pt/Ni@NGT nanostructure was used for the detection of glucose via catalyzing the oxidation of a substrate, 3,3′,5,5′-tetramethylbenzidine (TMB), to form a blue product (ox-TMB), thereby enabling colorimetric assay for enzymatically generated H2O2. The nanostructure exhibited excellent biocompatibility and led to highly efficient immobilization and retention of GOx. The method has a linear response in the 43 pM to 220 μM glucose concentration range, a detection limit as low as 1 pM and a limit of quantification of 3.4pM, along with good reproducibility(< 3%). A paper based visual microfluidic assay was also worked out that has an analytical range that extends from 0.1–50 mM. It is simple and rapid enough to be useful as a glucose home test.. The method was successfully applied to the determination of glucose in tear and saliva samples.

A metal organic framework (MOF) of type Fe(III)-BTC (where BTC is 1,3,5-benzenetricarboxylic acid) was utilized to construct an integrated system for cascade colorimetric determination of glucose. The MOF performs a dual function in acting (a) as a peroxidase (POx) mimic, and (b) as a solid support for immobilization of glucose oxidase (GOx). The MOF was prepared by a one-pot method. Glucose is consumed while H2O2 is produced during the enzymatic oxidation by GOx. In the presence of H2O2, the POx mimic catalytically oxidizes 3,3′,5,5′-tetramethylbenzidine (TMB) to form a blue-green product. The absorbance of oxidized TMB (measured at 652 nm) increases linearly in the 5.0–100 μM glucose concentration range, and the detection limit is 2.4 μM. The GOx@Fe-BTC MOF was successfully applied to the determination of glucose in serum.

Nitrogen-doped graphene quantum dots (N-GQDs) were prepared from dicyandiamide and then used as both an electrochemiluminescence (ECL) emitter and a reductant to produce gold nanoparticles (Au-N-GQDs) on their surface without using any reagent. In order to avoid resonance energy transfer, the Au-N-GQDs were stabilized with chitosan. Transmission electron microscopy (TEM), energy dispersive X-ray spectroscopy (EDX), UV-vis spectroscopy (UV-vis) and ECL methods were used to characterize the nanocomposite. The materials was placed on a glassy carbon electrode (GCE), and the ECL signals are found to be strongly quenched by hydrogen peroxide that is enzymatically produced by oxidation of glucose. With the applied typical potential of −1.7 V, the ECL of the Au-N-GQDs modified GCE decreases linearly in the 10 nM to 5.0 μM glucose concentration range, and the lower detection limit is 3.3 nM. The influence of H2O2 to the signal has been discussed and a possible mechanism has been presented.

An enzyme-metal organic framework (MOF) composite with saucer-like structure was prepared via one-pot synthesis from ficin (a cysteine proteolytic enzyme with POx activity), zinc(II) ions and 2-methylimidazole. The composites exhibit a 2.5-fold higher catalytic activity and stronger affinity for substrates compared to free ficin. This was exploited to design a colorimetric assay for the determination of glucose. The addition of glucose oxidase causes the formation of H2O2 which is catalytically oxidized by ficin to form a blue coloration that can be measured at 652 nm. The assay has a 0.12 μM detection limit and excellent selectivity. It was successfully applied to the determination of glucose in diluted serum samples.

Carbon quantum dots (CQDs) with peroxidase-mimicking activity were successfully prepared from litchi rind. A colorimetric method for glucose determination was developed based on etching of gold nanorods (GNRs) using CQDs as peroxidase mimetic. The glucose oxidase-catalyzed oxidation of glucose leads to the generation of H2O2 which oxidizes added iodide under formation of elemental iodine under the catalytic action of CQDs. Iodine then etches the GNRs along the longitudinal direction due to the higher reaction activities at the tips of GNRs. This results in a stepwise decrease in the maximum absorption wavelength of the GNRs, from initially 953 nm to finally 645 nm. Under the optimized conditions, the shift in the maximum absorption wavelength decreases linearly in the 0.01–2.0 mM glucose concentration range, and the detection limit is 3.0 μM. Importantly, this method was applied to the determination of glucose in human serum. It is perceived that the CQDs are valuable peroxidase mimics due to their ease of preparation, low costs and stable catalytic activity.

This paper reports on a colorimetric assay for H2O2 and glucose. It is based on the use of human serum albumin-templated MnO2 nanosheets that possess oxidase-like activity. They are capable of oxidizing 3,3',5,5'-tetramethylbenzidine (TMB) with oxygen to give a blue product (oxTMB) with an absorbance maximum at 652 nm. When H2O2 is introduced, the MnO2 nanosheets are reduced to Mn(II) ions, and this inhibits the formation of oxTMB. Based on these findings, a colorimetric assay was established for H2O2 that has a 0.56 μM detection limit. If glucose is oxidized by glucose oxidase under formation of H2O2, the nanosheets can be used to quantify H2O2 and thereby to sense glucose. Response is linear in the 0.5 μM to 50 μM glucose concentration range, and the detection limit is 0.32 μM. The method was applied to the determination of glucose in spiked serum samples and gave satisficatory results.

We report on a sensitive and selective fluorescent assay utilizing native carbon dots (CDs) as signal transducers. The optical probes 2,2′-azinobis(3-ethylbenzothiazoline-6-sulfonate) (ABTS) or 3,3′-diaminobenzidine (DAB) were employed as substrates of horseradish peroxidase (HRP). It was found that the corresponding oxidation products (ox-ABTS or ox-DAB) quench the fluorescence of CDs, mainly via photoinduced electron transfer in case of ox-ABTS, and via aggregation and inner filter effect in case of ox-DAB. By coupling with bienzyme (glucose oxidase and HRP)-mediated biocatalytic reactions, the method was applied to the determination of hydrogen peroxide and glucose. In case of ABTS as the substrate of HRP, a wide linear range (0.05 to 100 μM) and a very low detection limit (10 nM) for glucose were attained. The method was applied to the determination of glucose in human serum and the results were found to agree well with data provided by a local hospital.

This article describes an electrochemical glucose biosensor that is based on the immobilization of the enzyme glucose oxidase (GOx) on a glassy carbon electrode that was modified with silver-ZnO hybrid nanorods (HNRs). The HNRs containing different fractions of silver were synthesized by a one-step solvothermal method. Transmission electron microscopy, energy dispersive spectroscopy and X-ray diffraction confirmed the formation of these HNRs. FTIR spectroscopy and cyclic voltammetry demonstrated that the enzyme on the HNRs retained its native structure and bioactivity. The HNRs containing 11.26 wt% silver produced the best electrochemical response and direct electron transfer between enzyme and electrode surface. The sensor responds to glucose with two linear ranges (from 0.01 to 0.1 mM and from 0.1 to 1.5 mM). The sensitivity is 18.7 mA∙ M−1 ∙ cm−2, and the detection limit is 5 μM (at an SNR of 3). The biosensor is selective, acceptably stable, and well reproducible. It was successfully applied to the quantitation of glucose in human serum, and results were within −8.1 % and +6.5 % of data obtained with a reference method.

Greigite magnetic nanoparticles (Fe3S4-MNPs) were prepared and reveal a peroxidase-like activity. Kinetic studies revealed a pseudo-enzymatic activity that is much higher than that of other magnetic nanomaterial-based enzyme mimetics. This finding was exploited to design a photometric enzymatic glucose assay based on the formation of H2O2 during enzymatic oxidation of glucose by glucose oxidase, and the formation of a blue product from an enzyme substrate that is catalytically oxidized by H2O2 in the presence of Fe3S4-MNPs. Glucose can be detected in the 2 to 100 μM concentration range, and the low detection limit is 0.16 μM. The method was applied to quantify glucose in human serum. In our perception, this enzyme mimetic has a large potential in that it may be used in other oxidase based assays, but also in ELISAs.

Isotropic silver nanoparticles (iAg NPs) can be easily prepared at low costs, have a low electrochemical potential and high extinction coefficient. An effective colorimetric assay for H2O2 is reported here based on the finding that H2O2 can induce the shape transformation of citrate-capped iAg NPs with the help of citrate. The substantial shape variation affords an apparent surface plasmon resonance (SPR) shift, accompanied by a vivid color change from light yellow to mauve. The color change can be observed visually if the concentration of H2O2 is 2 μM or higher. A good linear relationship was obtained over the concentration range of 0.2-32 μM with a limit of detection of 90 nM. By making use of glucose oxidase, the method is further extended to glucose detection. Glucose at a concentration as low as 10 μM can be well determined with bare eyes. Benefitting from the high selectivity, the detection of glucose in human serum is realized, and the results are in good agreement with those provided by a clinical analyzer. Graphical abstract Schematic presentation of a colorimetric assay for H2O2 and glucose based on citrate-promoted H2O2-mediated shape transformation of the isotropic silver nanoparticles (Ag NPs). The shape variation of isotropic Ag NPs induces a color change from light yellow to mauve.

It is reported that a mixture of WS2 nanosheets (WS2 NS) and silver nanoclusters (AgNCs) displays strongly enhanced peroxidase-mimicking activity. The catalytic effect of the mixture was studied by colorimetry, fluorometry, chemiluminescence (CL) and electrochemistry. The effect is interpreted in terms of a difference between the Fermi energy level of the two nanomaterials. This leads to the formation of charge separation regions which act as active sites for enzyme mimetic interaction with the substrates. The mixture of WS2 NS and AgNCs was exploited for the non-enzymatic determination of H2O2 and glucose. A stopped-flow method was applied as a sensitive CL detection system using the bicarbonate-H2O2 reaction. The mixture has a powerful peroxidase mimicking activity on the bicarbonate-H2O2 CL reaction, and this effect is much larger than that of any single constituent. In addition, the CL emission is improved several times by using the stopped-flow technique. Under optimum condition, H2O2 can be determined in the 2.5–1500 nM concentration range. Moreover, glucose levels in human serum can be quantified via glucose oxidase based oxidation which leads to the generation of H2O2. Using this CL assay, a linear relationship was obtained between the intensity of the CL emission and glucose concentration in the range of 0.03–20 μM, with a limit of detection (3S) of 13 nM.

An optical method is described for the quantitation of glucose by using oxygen-deficient α-MoO3-x nanoflakes. It is based on the use of glucose oxidase (GOx) which produces hydrogen peroxide on oxidation of glucose. Hydrogen peroxide then oxidizes the α-MoO3-x nanoflakes, and this results in a visible color change from blue to colorless. The color change can be measured photometrically at 740 nm. The method has a 68 nM detection limit.

This work presents a microfluidic paper-based analytical device (μPAD) for glucose determination using a supported metal-organic framework (MOF) acting as a peroxidase mimic. The catalytic action of glucose oxidase (GOx) on glucose causes the formation of H2O2, and the MOF causes the oxidation of 3,3′,5,5′-tetramethylbenzidine (TMB) by H2O2 to form a blue-green product with an absorption peak at 650 nm in the detection zone. A digital camera and the iOS feature of a smartphone are used for the quantitation of glucose with the S coordinate of the HSV color space as the analytical parameter. Different factors such as the concentration of TMB, GOx and MOF, pH and buffer, sample volume, reaction time and reagent position in the μPAD were optimized. Under optimal conditions, the value for the S coordinate increases linearly up to 150 μmol·L−1 glucose concentrations, with a 2.5 μmol·L−1 detection limit. The μPAD remains stable for 21 days under conventional storage conditions. Such an enzyme mimetic-based assay to glucose determination using Fe-MIL-101 MOF implemented in a microfluidic paper-based device possesses advantages over enzyme-based assays in terms of costs, durability and stability compared to other existing glucose determination methods. The procedure was applied to the determination of glucose in (spiked) serum and urine.

Reduced graphene oxide (RGO) was used to construct a bienzyme biosensor containing horseradish peroxidase (HRP) and glucose oxidase (GOx). A poly(toluidine blue) (pTB) film containing RGO acted as both enzyme immobilization matrix and electron transfer mediator. The bienzyme biosensor was characterized by electrochemical techniques and displays a highly sensitive amperometric response to glucose and hydrogen peroxide (H2O2) at a potential as low as −0.1 V (vs. SCE). It is shown that use of RGO causes a strong enhancement on the amperometric responses. H2O2 formed by the action of GOx in the presence of oxygen can be further reduced by HRP in the pTB film contacting the RGO modified electrode. In the absence of oxygen, glucose oxidation proceeds by another mechanism in which electron transfer occurs from GOx to the electrode and with pTB acting as the mediator. Amperometric responses to glucose and H2O2 follow Michaelis-Menten kinetics. The experimental conditions were optimized, and under these conditions glucose can be determined in the 80 μM to 3.0 mM range with a detection limit of 50 μM. H2O2, in turn, can be quantified in up to 30.0 μM concentration with a detection limit of 0.2 μM. The bienzyme biosensor is reproducible, repeatable and stable. Finally, it has been successfully applied to the determination of glucose in plasma samples.

We report on an indirect optical method for the determination of glucose via the detection of hydrogen peroxide (H2O2) that is generated during the glucose oxidase (GOx) catalyzed oxidation of glucose. It is based on the finding that the ultraviolet (~374 nm) and visible (~525 nm) photoluminescence of pristine zinc oxide (ZnO) nanoparticles strongly depends on the concentration of H2O2 in water solution. Photoluminescence is quenched by up to 90 % at a 100 mM level of H2O2. The sensor constructed by immobilizing GOx on ZnO nanoparticles enabled glucose to be continuously monitored in the 10 mM to 130 mM concentration range, and the limit of detection is 10 mM. This enzymatic sensing scheme is supposed to be applicable to monitoring glucose in the food, beverage and fermentation industries. It has a wide scope in that it may be extended to numerous other substrate or enzyme activity assays based on the formation of H2O2, and of assays based on the consumption of H2O2 by peroxidases.

An enzymatic glucose biosensor was developed that is making use of microspheres consisting of an m-aminophenol based resin decorated with silver nanoparticles (AgNP/MAPR). It was applied to the detection of H2O2 and, if loaded with glucose oxidase (GOx), to the determination of glucose. The AgNPs were thermally immobilized on the MAPR microspheres. The AgNP/MAPR microspheres were deposited on a glassy carbon electrode (GCE) by surface casting. The resultant electrode exhibits remarkable catalytic performance in terms of H2O2 reduction. The sensor gives an amperometric response to H2O2 within

We report on a bienzyme-channeling sensor for sensing glucose without the aid of mediator. It was fabricated by cross-linking horseradish peroxidase (HRP) and glucose oxidase (GOx) on a glassy carbon electrode modified with multiwalled carbon nanotubes (MWNTs). The bienzyme was cross-linked with the MWNTs by glutaraldehyde and bovine serum albumin. The MWNTs were employed to accelerate the electron transfer between immobilized HRP and electrode. Glucose was sensed by amperometric reduction of enzymatically generated H2O2 at an applied voltage of −50 mV (vs. Ag/AgCl). Factors influencing the preparation and performance of the bienzyme electrode were investigated in detail. The biosensor exhibited a fast and linear response to glucose in the concentration range from 0.4 to 15 mM, with a detection limit of 0.4 mM. The sensor exhibited good selectivity and durability, with a long-term relative standard deviation of

Fe3O4 nanoparticles were deposited on sheets of graphene oxide (GO) by a precipitation method, and glucose oxidase (GOx) was then immobilized on this material to produce a GOx/Fe3O4/GO magnetic nanocomposite containing crosslinked enzyme clusters. The 3-component composite functions as a binary enzyme that was employed in a photometric method for the determination of glucose and hydrogen peroxide where the GOx/Fe3O4/GO nanoparticles cause the generation of H2O2 which, in turn, oxidize the substrate N,N-diethyl-p-phenylenediamine to form a purple product with an absorption maximum at 550 nm. The absorbance at 550 nm can be correlated to the concentration of glucose and/or hydrogen peroxide. Under optimized conditions, the calibration plot is linear in the 0.5 to 600 μM glucose concentration range, and the detection limit is 0.2 μM. The respective plot for H2O2 ranges from 0.1 to 10 μM, and the detection limit is 0.04 μM. The method was successfully applied to the determination of glucose in human serum samples. The GOx/Fe3O4/GO nanoparticles are reusable.

A novel glucose biosensor is presented as that based on a glassy carbon electrode modified with hollow gold nanoparticles (HGNs) and glucose oxidase. The sensor exhibits a better differential pulse voltammetric response towards glucose than the one based on conventional gold nanoparticles of the same size. This is attributed to the good biological conductivity and biocompatibility of HGNs. Under the optimal conditions, the sensor displays a linear range from 2.0 × 10−6 to 4.6 × 10−5 M of glucose, with a detection limit of 1.6 × 10−6 M (S/N = 3). Good reproducibility, stability and no interference make this biosensor applicable to the determination of glucose in samples such as sports drinks.

The aim of this work was to further evaluate the effect of colloidal solutions of gold nanoparticles (Au-NPs) on the performance of a carbon rod electrode modified with glucose oxidase. The amperometric response of the system at +0.3 V vs. Ag/AgCl was studied in the absence and in the presence of Au-NPs (6 nm and 13 nm in diameter) and in presence of N-methylphenazonium methyl sulfate (PMS) at pH 6.0. This study shows that the application of

A surface plasmon resonance (SPR) based biosensor for glucose is presented in which a thin gold film modified with polypyrrole and glucose oxidase (PPy-GOx) acts as the sensor chip. It is based on SPR response to the change of refractive index of PPy-GOx film by the enzymatic catalytic reaction. The co-electropolymerization of pyrrole and GOx was carried out under cyclic voltammetric conditions, and simultaneously monitored by in-situ SPR. It has been revealed that the enzymatic reaction between GOx and PPy in the presence of glucose can lead to distinct changes in the SPR signal. From the experiments, a linear relationship was obtained in the range 1–100 μmol L−1 between glucose concentration and the rate of redox transformation of PPy. The detection limit was 0.5 μmol L−1 (S/N = 3) and recoveries were 95.2–102.7%.

The electrochemistry of glucose oxidase (GOx) immobilized on a graphite rod electrode modified by gold nanoparticles (Au-NPs) was studied. Two types of amperometric glucose sensors based on GOx immobilized and Au-NPs modified working electrode (Au-NPs/GOx/graphite and GOx/Au-NPs/graphite) were designed and tested in the presence and the absence of N-methylphenazonium methyl sulphate in different buffers. Results were compared to those obtained with similar electrodes not containing Au-NPs (GOx/graphite). This study shows that the application of Au-NPs increases the rate of mediated electron transfer. Major analytical characteristics of the amperometric biosensor based on GOx and 13 nm diameter Au-NPs were determined. The analytical signal was linearly related to glucose concentration in the range from 0.1 to 10 mmol L−1. The detection limit for glucose was found within 0.1 mmol L−1 and 0.08 mmol L−1 and the relative standard deviation in the range of 0.1–100 mol L−1 was 0.04–0.39%. The τ1/2 of Vmax characterizes the storage stability of sensors: this parameter for the developed GOx/graphite electrode was 49.3 days and for GOx/Au-NPs/graphite electrode was 19.5 days. The sensor might be suitable for determination of glucose in beverages and/or in food.

A sensitive method was developed for the determination of the hebicide atrazine. It based on the use of glucose oxidase that is self-assembled on aligned carbon nanotubes on the surface of a copper electrode. The surface morphology and electrochemical properties of the electrode were characterized by field emission scanning electron microscopy and cyclic voltammetry. The effects of buffer solution and incubation time on the response of the electrode were investigated. Response to atrazine is linear in the range from 0.58 µM to 42 µM, and the detection limit is 39 nM. The performance of the biosensor was verified by determination of atrazine in environmental water samples.

A polyion complex membrane containing peroxidase and toluidine blue (PIC-POx-TB) was prepared by mixing polystyrene sulfonate, POx, TB, and poly-l-lysine solutions on the glassy carbon electrode. Current response to hydrogen peroxide on PIC-POx-TB electrode was measured at a potential of −0.25 V vs. Ag/AgCl: the response time was ca. 2 min, and the response current was proportional to the hydrogen peroxide concentration up to 50 μM. The lower detection limit was 1 μM (signal-to-noise ratio, S/N = 3). Current ratio between l-ascorbate and hydrogen peroxide at the same concentration was determined to be several percent. The PIC-POx-TB electrode was used as a hydrogen peroxide sensor. On the PIC-POx-TB electrode, glucose oxidase (GOx) was attached by the glutaraldehyde method. The GOx-PIC-POx-TB electrode was used for glucose detection. Response to glucose was proportional to the glucose concentration up to 100 μM, and lower detection limit was 5 μM (S/N = 3). The response current was not affected by l-ascorbate.

Amperometric biosensors are widely used for clinical, food industry and environmental control. A universal platform allowing immobilization of different enzymes could provide a fast and easy way to design new sensors, but the main drawback effect with oxidase based biosensors is the production of hydrogen peroxide. The direct electron transfer is a way to limit the H2O2 production. A modified electrode described by Zhao et al. (Bioelectrochemistry, 69(2):158, 2006), based on immobilization of glucose oxidase/colloidal gold nanoparticles on a glassy carbon electrode by Nafion film, has been used. Its sensitivity is 0.4 μA mM−1 cm−2, reproducibility is 3.0%, detection limit is 0.37 mM, response to glucose is linear up to 20 mM; limit of detection is 0.37 mM and response time is about 1.5 min. This sensor displays a formal redox potential compatible with a direct electron transfer, and has been tested for its response in time and GOx denaturation by X-ray photoelectron spectroscopy. Vanishing of disulphide bonds of GOx has been observed after a period in a saturating solution of glucose but this does not appear determinant in loss of enzyme activity.