Glucose Oxidase In Solution Research Articles

Nanozyme–Cellulose Hydrogel Composites Enabling Cascade Catalysis for the Colorimetric Detection of Glucose

Catalytic cascades obtained from the combination of nanozymes, which are nanomaterials with enzyme-like activity, and natural enzymes have drawn much attention for biosensing and biomedical applications. A key consideration in the development of cascade reaction systems is the integration of nanozymes with enzymes to boost the overall catalytic performance. Here, we report an efficient one-pot approach for the preparation of an enzyme–nanozyme hydrogel composite for cascade catalysis. Prussian blue (PB) nanoparticles (NPs) were prepared by using mild synthetic conditions in a cellulose-based hydrogel network in the presence of glucose oxidase (GOx), resulting in the simultaneous immobilization of PB NPs and active GOx in the hydrogel. This integrated system not only displays peroxidase-like activity relative to the PB NPs but also reveals an enhanced cascade catalytic performance for the colorimetric detection of glucose due to the proximity effect of the enzyme–nanozyme system within the hydrogel matrix. Compared to the analogue mixture with GOx in solution, the composite hydrogel shows enhanced glucose detection and improved stability. The developed colorimetric assay was successfully applied for the analysis of glucose in human serum samples, demonstrating its potential in clinical diagnosis. The versatility of this one-pot protocol holds promise for the development of different multienzyme systems, leading to efficient cascade catalysis for sensing applications.

AuPt Bimetallic Nanozymes for Enhanced Glucose Catalytic Oxidase.

Au metal nanoparticles as artificial nanozymes have attracted wide interest in biotechnology due to high stability and easy synthesis. Unfortunately, its catalytic activity is limited by the uniform surface electron distribution, fundamentally affecting the oxidation efficiency of glucose. Here, we synthesized AuPt bimetallic nanoparticles with unique surface electron structure due to the coupling effect of the two metal components, achieving improved glucose catalytic oxidase. Because of the effective work function difference between the two metals in AuPt, the electrons will transfer from Au to accumulate on Pt, simultaneously contributing to the substantial enhancement of Au-induced glucose oxidase and Pt-induced catalase performance. We systematically studied the enzyme-catalytic efficiency of AuPt with varied two metal proportions, in which Au:Pt at 3:1 showed the highest catalytic efficiency of glucose oxidase in solution. The AuPt nanoparticles were further co-cultured with cells and also showed excellent biological activity for glucose oxidase. This work demonstrates that the physicochemical properties between different metals can be exploited for engineering high-performance metal nanoparticle-based nanozymes, which opens up a new way to rationally design and optimize artificial nanozymes to mimic natural enzymes.

Increased thermal stability of a glucose oxidase biosensor under high hydrostatic pressure

We report the effects of high hydrostatic pressure (HHP), immobilization in electrochemically generated poly-o-phenylenediamine nano-films, and reticulation with glutaraldehyde on the thermal stability of glucose oxidase (GOx). The pseudo-first-order rate constant of inactivation of immobilized GOx inactivated at 70 °C and atmospheric pressure was 20.6 times smaller than that of GOx in solution under the same conditions. Immobilized GOx inactivated at 70 °C and 180 MPa was 87.6 times more stable than GOx in solution inactivated at 70 °C and atmospheric pressure. However, applying high pressure during electropolymerization or cross-linking with glutaraldehyde only had minor influences on GOx thermal stability. The stabilizing effect of HHP was not retained upon depressurization.

Enhancing online protein isolation as intact species from soy flour samples by actively modulated two-dimensional liquid chromatography (2D-LC)

In this study, an enhanced fully automated approach is described for the protein isolation from soy flour samples by two-dimensional liquid chromatography with active modulation interface. The use of two multi-port switching valves is proposed to on-line connect the first to the second dimension column, thus overcoming the problems associated with the re-mixing effects and incompatibility of eluent composition and pH. A 5-cm long C4 analytical column installed in the interface device allows to focus the proteins coming from the first column (size exclusion chromatography), before their selective elution in the second column (reversed-phase). A trap washing step was included in the total workflow, as a desalting step to remove buffer residues from the eluent of the first column and to enhance the chromatographic performances of the second column. The experimental conditions were optimized by analyses of mixed standard solutions of bovine serum albumin, glucose oxidase, immunoglobulin A, thyroglobulin and myoglobin. Then, the optimized 2D-LC method was applied to the protein analysis in extracts of soy flour, known worldwide as one of the major food allergen sources, with the final aim to recovery sufficient protein amounts for the molecular characterization and the assessment of the pattern of allergenic components.

3D Multilayered paper- and thread/paper-based microfluidic devices for bioassays.

In this paper we describe the fabrication of novel 3D microfluidic paper-based analytical devices (3D-μPADs) and a 3D microfluidic thread/paper-based analytical device (3D-μTPAD) to detect glucose and BSA through colorimetric assays. The 3D-μPAD and 3D-μTPAD consisted of three (wax, heat pressed wax-printed paper, single-sided tape) and four (hole-punched single-sided tape, blank chromatography circles, heat-pressed wax-printed paper, hole-punched single-sided tape containing trifurcated thread) layers, respectively. The saturation curves for each assay were generated for all platforms. For the glucose assay, a solution of glucose oxidase (GOx), horseradish peroxidase, and potassium iodide was flowed through each platform and, upon contact with glucose, generated a yellow-brown color indicative of the oxidation of iodide to iodine. For the protein assay, BSA was flowed through each device and, upon contact with citrate buffer and tetrabromophenol blue, resulted in a color change from yellow to blue. The devices were dried, scanned, and analyzed yielding a correlation between either yellow intensity and glucose concentration or cyan intensity and BSA concentration. A similar glucose assay, using unknown concentrations of glucose in artificial urine, was conducted and, when compared to the saturation curve, showed good correlation between the theoretical and actual concentrations (percent differences <10%). The development of 3D-μPADs and 3D-μTPADs can further facilitate the use of these platforms for colorimetric bioassays.

Designing Microreactors Resembling Cellular Microenvironment via Polyamine-Mediated Nanoparticle-Assembly for Tuning Glucose Oxidase Kinetics.

Spatial confinement of glucose oxidase (GOx) in the hollow interior of a bioinspired matrix via polyamine mediated silica nanoparticle assembly under environmentally benign conditions is demonstrated herein. In a similarity to the biosilicification processes in diatoms, we use poly(allylamine hydrochloride) (PAH) to direct the assembly of silica nanoparticles on CaCO3 spheres as the removable core. When this assembly process is performed on the CaCO3 spheres, which are preloaded with GOx in a postsynthesis method, microspheres encapsulating GOx are formed. Interestingly, the encapsulated GOx in these microreactors exhibits activity with a Michaelis-Menten constant ( KM) that is 2- to 3-fold less compared with the free enzyme in the solution. While the microenvironment of the organic (PAH)-inorganic (silica) hybrid system can be advantageous for the substrate to interact with enzyme, the effective pH in the vicinity of the entrapped enzyme may also be accountable for the improved activity, resulting in the lower apparent KM and enhanced specificity constant ( kcat/ KM). A 2-fold higher thermal stability of the encapsulated GOx compared with free GOx in solution further demonstrates the efficacy of the integrated architecture. Additionally, the PAH by virtue of its buffering capability allows the microspheres in imparting pH stability to the encapsulated GOx. Therefore, the method is not only a greener process for performing enzyme immobilization but also anticipated to aid in designing microreactors for enhanced enzyme activity.

Thread/paper- and paper-based microfluidic devices for glucose assays employing artificial neural networks.

This paper describes the fabrication of and data collection from two microfluidic devices: a microfluidic thread/paper based analytical device (μTPAD) and 3D microfluidic paper-based analytical device (μPAD). Flowing solutions of glucose oxidase (GOx), horseradish peroxidase (HRP), and potassium iodide (KI), through each device, on contact with glucose, generated a calibration curve for each platform. The resultant yellow-brown color from the reaction indicates oxidation of iodide to iodine. The devices were dried, scanned, and analyzed yielding a correlation between yellow intensity and glucose concentration. A similar procedure, using an unknown concentration of glucose in artificial urine, is conducted and compared to the calibration curve to obtain the unknown value. Studies to quantify glucose in artificial urine showed good correlation between the theoretical and actual concentrations, as percent differences were ≤13.0%. An ANN was trained on the four-channel CMYK color data from 54 μTPAD and 160 μPAD analysis sites and Pearson correlation coefficients of R = 0.96491 and 0.9739, respectively, were obtained. The ANN was able to correctly classify 94.4% (51 of 54 samples) and 91.2% (146 of 160 samples) of the μTPAD and μPAD analysis sites, respectively. The development of this technology combined with ANN should further facilitate the use of these platforms for colorimetric analysis of other analytes.

Electrodeposition of Both Carbon Nanotube and Glucose Oxidase on Pt Eectrode Using a Dispersed Electrolytic Solution

Immobilization of the enzyme is one of the most critical processes for the fabrication of an enzyme sensor, since it will highly influence properties of the obtained sensor. Various procedure have been proposed for a the preparation of glucose sensor, such as covalent attachment, cross-linking, hydrogel entrapment, polymer film entrapment, and the combination of two or more methods. Among the various techniques, the electrodeposition method is interesting owing to its simple preparation, miniaturization, and precise localization of enzyme. On the other hand, nanocarbons (NCs), such as carbon nanotubes (CNTs) and graphenes, are extremely attractive in biosensor application, since they can combine properties of the high surface area, high stability and good electrical conductivity. However, NCs is not soluble in aqueous solution, which is the least media to dissolve enzyme without reducing its activity. The use of surfactants is a candidate to preparer a disperse NCs in enzyme solution, while this may also reduce the enzyme activity. Therefore, processes of enzyme immobilization and NCs immobilization are commonly performed separately using different solutions. In this study, stable dispersed solutions of glucose oxidase (GOx) and multi-walled CNT were developed using gellan gum, which is a polysaccharide manufactured by microbial fermentation used widely as a gelling agents. By using this CNT/GOx dispersed solution, both CNT and GOx were successfully immobilized on Pt-Ir electrode by a simple step of applying a constant potential of 1.3 V（vs. Ag/AgCl) to the electrode in this solution. The electropolymerization of o-phenylenediamine was followed in order to increase the stability of enzyme-immobilized electrode. The CNT/GOx immobilized electrode performed as a glucose sensor with a high sensor sensitivity. This indicate that the introduction of CNT in GOx-immobilized film increased the efficiency of electron transfer between the electrode and generated hydrogen peroxide. In addition, the reproducibility of electrode fabrication was satisfactorily improved by the use of gellan gum compared with that using Triton X-100 as a dispersing agent.

Fluorescence Quenching-Based Evaluation of Glucose Oxidase Composite with Conducting Polymer, Polypyrrole

Glucose oxidase (GOx) composites with conducting polymers (e.g., polypyrrole (Ppy)) are excellent nanobiomaterials suitable for the design of bioelectronic devices such as biosensors and biofuel cells. Here, we address the spectroscopic properties of GOx, flavin adenine dinucleotide (FAD), and composites of these compounds with polypyrrole (Ppy). The exploration of native GOx and FAD solutions confirmed that about 5% of FAD dissociated from GOx during the period of solution preparation, and this fraction remained constant for 1 month. It has been found that the Ppy, which formed composites with FAD and GOx, facilitated the removal of FAD molecules from GOx and twice reduced the fluorescence decay rate. Differences in the FAD and Ppy average fluorescence relaxation times showed that the FAD composite with Ppy and Ppy effectively quenched the FAD fluorescence and FAD could not freely unfold. The intramolecular electron transfer took place between adenine and isoalloxazine moieties over the first 5 ps after ...

An Amperometric Glucose Biosensor Based on Poly (Pyrrole‐2‐Carboxylic Acid)/Glucose Oxidase Biocomposite

AbstractA newly developed amperometric glucose biosensor based on graphite rod (GR) working electrode modified with biocomposite consisting of poly (pyrrole‐2‐carboxylic acid) (PCPy) particles and enzyme glucose oxidase (GOx) was investigated. The PCPy particles were synthesized by chemical oxidative polymerization technique using H2O2 as initiator of polymerization reaction and modified covalently with the GOx (PCPy‐GOx) after activation of carboxyl groups located on the particles surface with a mixture of N‐(3‐dimethylaminopropyl)‐N′‐ethylcarbodiimide hydrochloride (EDC) and N‐hydroxysuccinimide (NHS). Then the PCPy‐GOx biocomposite was dispersed in a buffer solution containing a certain amount of bovine serum albumin (BSA). The resulting biocomposite suspension was adsorbed the on GR electrode surface with subsequent solvent airing and chemical cross‐linking of the proteins with glutaraldehyde vapour (GR/PCPy‐GOx). It was determined that the current response of the GR/PCPy‐GOx electrodes to glucose measured at +300 mV vs Cl reference electrode was influenced by the duration of the PCPy particles synthesis, pH of the GOx solution used for the PCPy particles modification and the amount of immobilized PCPy‐GOx biocomposite. An optimal pH of buffer solution for operation of the biosensor was found to be 8.0. Detection limit was determined as 0.039 mmol L−1 according signal to noise ratio (S/N: 3). The proposed glucose biosensor was tested in human serum samples.

Pluronic‐Conjugated Enzyme Cascade for In Situ Oxidation in Biphasic Media

AbstractA Pluronic‐conjugated enzyme cascade was synthesized for catalyzing oxidation reactions using hydrogen peroxide (H2O2) as the oxidant. The synthesis started with encapsulating enzymes in the micelles of aldehyde‐functionalized Pluronic (PL) containing bovine serum albumin (BSA). Schiff‐base bonds formed between the amine groups of proteins and the aldehyde groups of the PL, which were reduced to a more stable form, resulting in enzyme–PL conjugates. The effects of operation parameters on the conjugate yield were examined using glucose oxidase (GOx) and horseradish peroxidase (HRP) as examples. The co‐localization of GOx and HRP was confirmed by Förster resonance energy transfer (FRET), from which the average distance between GOx and HRP was interpreted as 6.1 nm. The proximity effect was confirmed by adding a high concentration of catalase (CAT) to a solution of GOx–HRP–PL to catalyze the oxidation of ABTS. The GOx–HRP–PL conjugate was readily solubilized in organic solvents such as dimethyl sulfoxide, methanol or chloroform. Phenol oxidation with GOx–HRP–PL in dimethyl sulfoxide/water biphasic media was conducted using glucose as the substrate to generate H2O2 in situ. The multiple enzyme conjugate provided a 1.3‐fold higher removal rate compared to their native counterparts in free form. The GOx–HRP–PL conjugate could be readily recovered by centrifugation at 4 °C and 90 % of the initial activity remained after 10 cycles.

A correlation of results measured by cyclic voltammogram and impedance spectroscopy in glucose oxidase based biocatalysts

A new biocatalyst consisting of glucose oxidase (GOx) and polyethylenimine (PEI) immobilized on carbon nanotube (CNT) (CNT/PEI/GOx) was developed, while cyclic voltammogram (CV) behaviors of several related catalysts including the CNT/PEI/GOx were analyzed in terms of charge transfer resistances (R ct s) obtained by measuring Nyquist plots using electrochemical impedance spectroscopy (EIS). A qualitative correlation between the flavin adenine dinucleotide (FAD) redox reactivity measured by the CV and R ct was established. As factors affecting both the FAD reactivity and R ct , concentrations of GOx, glucose, and phosphate buffer solution, electrolyte pH and ambient condition were considered and evaluations of the catalysts using the CV curves and Nyquist plots confirmed that a pattern in the FAD reactivity was closely linked to that in the R ct , implying that FAD reactivities of the catalysts are predicted by the measurements of their R ct s. Even regarding performance of the enzymatic biofeul cells (EBCs) using the reacted catalysts, a pattern of the R ct s is compatible with that in the maximum power densities (MPDs) of the EBCs.

Screen-printed enzymatic glucose biosensor based on a composite made from multiwalled carbon nanotubes and palladium containing particles

A composite material consisting of multiwalled carbon nanotubes and palladium containing particles was synthesized and applied to the preparation of bulk-modified screen-printed carbon electrodes (Pd-MWCNT-SPCE) and surface-modified screen-printed carbon electrodes (Pd-MWCNT/SPCE). They were characterized by cyclic voltammetry and hydrodynamic chronoamperometry in solution of pH 7.5. Both electrodes were then modified with glucose oxidase (GOx) by drop-coating a solution of GOx and Nafion® on their surface. Glucose can be determined via enzymatically formed H2O2. In an alternative approach, gold nanoparticles (5 nm) were incorporated into the biolayer of the electrodes. The resulting electrodes of type GOx/Pd-MWCNT-SPCE and GOx-Au/Pd-MWCNT-SPCE showed acceptable analytical performance at working potentials between −0.20 V and −0.50 V in case of hydrodynamic chronoamperometry. Both electrodes can be operated best at a working potential of −0.40 V vs SCE, with acceptable linearity of the methods in sub mM concentration ranges and with LOQs of 0.14 mM and 0.07 mM for glucose for the GOx/Pd-MWCNT-SPCE and GOx-Au/Pd-MWCNT-SPCE, respectively. Incorporation of gold nanoparticles prolongs the operational lifetime of the electrodes by two weeks. The GOx/Pd-MWCNT-SPCE based method was applied to the determination of glucose in multifloral honey, and the GOx-Au/Pd-MWCNT-SPCE method to the determination of glucose in blood serum. In both cases there was a good agreement with the results obtained by commercially available equipment for determination of glucose.

Fabrication of enzyme-based coatings on intact multi-walled carbon nanotubes as highly effective electrodes in biofuel cells

CNTs need to be dispersed in aqueous solution for their successful use, and most methods to disperse CNTs rely on tedious and time-consuming acid-based oxidation. Here, we report the simple dispersion of intact multi-walled carbon nanotubes (CNTs) by adding them directly into an aqueous solution of glucose oxidase (GOx), resulting in simultaneous CNT dispersion and facile enzyme immobilization through sequential enzyme adsorption, precipitation, and crosslinking (EAPC). The EAPC achieved high enzyme loading and stability because of crosslinked enzyme coatings on intact CNTs, while obviating the chemical pretreatment that can seriously damage the electron conductivity of CNTs. EAPC-driven GOx activity was 4.5- and 11-times higher than those of covalently-attached GOx (CA) on acid-treated CNTs and simply-adsorbed GOx (ADS) on intact CNTs, respectively. EAPC showed no decrease of GOx activity for 270 days. EAPC was employed to prepare the enzyme anodes for biofuel cells, and the EAPC anode produced 7.5-times higher power output than the CA anode. Even with a higher amount of bound non-conductive enzymes, the EAPC anode showed 1.7-fold higher electron transfer rate than the CA anode. The EAPC on intact CNTs can improve enzyme loading and stability with key routes of improved electron transfer in various biosensing and bioelectronics devices.

Nanoarmoring of Enzymes by Interlocking in Cellulose Fibers With Poly(Acrylic Acid).

A simple method for interlocking glucose oxidase (GOx) and horseradish peroxidase (HRP) in cellulose fibers using poly(acrylic acid) (PAA) as an armor around the enzyme, without any need for activation of the cellulose support, is reported here. The resulting enzyme paper is an inexpensive, stable, simple, wearable, and washable biosensor. PAA functions as a multifunctional tether to interlock the enzyme molecules around the paper fibers so that the enzymes are protected against thermal/chemical denaturation and not released from the paper when washed with a detergent. The decreased conformational entropy of the interlocked enzyme protected by the nanoarmor is likely responsible for increased enzyme stability to heat and chemical denaturants (retained ≥70 percent enzyme activity after washing with urea or SDS for 30min), and the polymer protects the enzyme against inactivation by proteases, bacteria, inhibitors, etc. The kinetics of the interlocked enzyme were similar to that of the enzyme in solution. The Vmax was 6(±0.5)mM per minute before washing, then increased slightly to 9(±1.4)mM per minute after washing with water. The Km was 22(±6.4mM), which was slightly higher compared to GOx in solution (25-27mM). Because the surface area of the paper does not limit the enzyme loading, about 20% of enzyme was successfully loaded onto the paper (0.2g enzyme per gram of paper), and ≥95% of the enzyme was retained after washing. Interlocking works with other enzymes such as laccase, where ≥60% of the enzyme activity is retained. This novel methodology provides a low cost, simple, modular approach of achieving high enzyme loadings in ordinary filter paper, not limited by cellulose surface area, and there has been no need for complex methods of enzyme engineering or toxic methods of activation of the solid support to prepare highly active biocatalysts.

Impact of additives on the formation of protein aggregates and viscosity in concentrated protein solutions

In concentrated protein solutions attractive protein interactions may not only cause the formation of undesired aggregates but also of gel-like networks with elevated viscosity. To guarantee stable biopharmaceutical processes and safe formulations, both phenomenons have to be avoided as these may hinder regular processing steps. This work screens the impact of additives on both phase behavior and viscosity of concentrated protein solutions. For this purpose, additives known for stabilizing proteins in solution or modulating the dynamic viscosity were selected. These additives were PEG 300, PEG 1000, glycerol, glycine, NaCl and ArgHCl. Concentrated lysozyme and glucose oxidase solutions at pH 3 and 9 served as model systems. Fourier-transformed-infrared spectroscopy was chosen to determine the conformational stability of selected protein samples. Influencing protein interactions, the impact of additives was strongly dependent on pH. Of all additives investigated, glycine was the only one that maintained protein conformational and colloidal stability while decreasing the dynamic viscosity. Low concentrations of NaCl showed the same effect, but increasing concentrations resulted in visible protein aggregation.

A facile and simple polyaniline-poly(ethylene oxide) based glucose biosensor

In this work, the fabrication and performance of a simple and efficient glucose biosensor based on chemically synthesized polyaniline-poly(ethylene oxide) nanocomposite (PAni-PEO) have been demonstrated. The nanocomposite was synthesized through rapid-mixing polymerization and characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), and Fourier transform infrared spectroscopy (FT-IR). The nanocomposite and glucose oxidase (GOx) solutions were placed on a platinum electrode by drop-casting, to produce a glucose biosensor that was characterized by cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS), and chronoamperometry. Under optimal conditions, the biosensor showed a linear range from 1 to 10mM (R2=0.990) with a high sensitivity of 16.04μAmM−1cm−2 and a detection limit of 0.82mM. The interference from ascorbic acid (AA) and uric acid (UA) was also investigated. The results indicated that the biosensor exhibited a satisfactory linear range, sensibility, and selectivity for use as a glucose biosensor, considering the normal range of approximately 4–6mM of glucose concentration in human blood.

Intensifying the O2-dependent heterogeneous biocatalysis: Superoxygenation of solid support from H2O2 by a catalase tailor-made for effective immobilization

Besides merely destroying H2O2, an important use of the catalase reaction, H2O2→1/2 O2+H2O, is to supply O2 to oxygenation reactions. Due to convenient spatiotemporal control over O2 release, oxygenation from H2O2 is useful in particular for enzymatic reactions confined to solid supports. Because commercial catalases are difficult to immobilize, we have developed a one-step procedure of purification and immobilization of Bordetella pertussis catalase, recombinantly produced in Escherichia coli. Fusion of the catalase to a positively charged binding module enabled effective immobilization of the chimeric enzyme on anionic support (Relisorb SP 400), giving a controllable activity loading of between 5000 and 100,000 units/g support. Use of the immobilized catalase in combination with H2O2 feeding provided O2 to the reaction of glucose oxidase in solution for a range of volumetric conversion rates (0.2–1.5mM/min). Using optical sensing to measure the O2 concentration in the liquid but also in the solid phase, we showed that internal superoxygenation of the support was made possible under these conditions, resulting in an inverted (that is, negative) O2 concentration gradient between the bulk and the particle and allowing the internal O2 concentration to exceed by up to 4-fold the limit of atmospheric-pressure air saturation in solution. By tailored immobilization of B. pertussis catalase, therefore, an efficient biocatalytic system for hydrogen peroxide conversion in porous solid support was developed. This could find application for bubble-free oxygenation of O2-dependent enzymes co-immobilized with the catalase whereby enhanced internal availability of O2 would contribute to biocatalytic reaction intensification.

Effects of the surface morphologies of ZnO nanotube arrays on the performance of amperometric glucose sensors

Amperometric glucose sensors have been fabricated with glucose oxidase (GOx) immobilized on ZnO nanotubes (ZnONTs) by physical adsorption. The ZnONTs were formed through selective dissolution of ZnO nanorods (ZnONRs) which were hydrothermally synthesized on Au cylindrical spiral (AuCS) electrodes. With the etching temperature regulated, the surface morphologies of the ZnONT arrays were tailored and their effects on the performance of the corresponding glucose sensors were investigated. It is found that at 65°C the as-prepared ZnONT arrays show a Gaussian rough surface with larger surface area and better hydrophilicity, and have an effective solid–liquid interface with GOx solution, which further results in desirable GOx immobilization. Therefore favorable performance of the ZnONT-based glucose sensor was obtained, such as the sensitivity 2.63 μA/(mMcm2), linear range 0–6.5mM, low detection limit 8μM (S/N=3) and Michaelis-Menten constant 5.24mM, which are superior to that of the ZnONR-based one. Moreover, the ZnONT-based glucose sensor exhibits good long-term stability, and excellent anti-interference ability to uric acid and ascorbic acid. The results can also be used for the performance optimization and the process standardization of other ZnONT-based amperometric biosensors.

Mixed thread/paper-based microfluidic chips as a platform for glucose assays.

A novel microfluidic thread/paper-based analytical device (μTPAD) to detect glucose through a colorimetric assay is described. The μTPAD was fabricated from nylon thread trifurcated into three channels terminating at analysis sites comprised of circular zones of chromatography paper, which have previously been spotted with glucose of different concentrations. A solution of glucose oxidase (GOx), horseradish peroxidase (HRP), and potassium iodide (KI) is transported via capillary action to the analysis sites where a yellow-brown color is observed indicating oxidation of iodide to iodine. The device was then dried, scanned, and analyzed yielding a correlation between yellow intensity and glucose concentrations. Both a flat platform constructed mainly of tape, and a cone platform constructed from tape and polyvinyl chloride, are described. Studies to quantitate glucose in artificial urine showed good correlation using the μTPAD.