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• A smartphone-interfaced flow injection sensing system was developed. • An electrode was modified with Pd-PANI/Carbon microspheres@carbon nanotubes. • Sensitive determination of glucose was achieved in real human serum samples. Integrating a flow injection system with an electrochemical sensor controlled by a smartphone enables rapid, precise real-time monitoring and reduces analyte consumption, contamination and costs. An enzyme-free electrochemical sensor is presented for the monitoring of glucose, an important indicator of diabetes. The sensor integrates a smartphone and a flow injection amperometric system. The flow cell is fabricated from acrylic plastic and includes an electrochemical three-electrode cell that comprises a working electrode modified with a catalyst of palladium-polyaniline/carbon microspheres@carbon nanotubes (Pd-PANI/CM@CNTs/E) for the detection of glucose oxidation. In the optimal condition, the proposed system produced good analytical performances. The sensor determined glucose linearly in a range from 0.020 to 100 mM, with a sensitivity of 51.51 μA mM−1 cm−2, and a detection limit (LOD) of 0.0071 mM. The developed system also exhibited good repeatability, reproducibility, operational stability, and anti-interference properties, and accurately determined glucose levels in real human serum samples. This sensing platform provides an alternative tool for the development of a continuous glucose monitor system for clinical applications. [Display omitted] [ABSTRACT FROM AUTHOR]

In the present work, MoS 2 nanosheets were composited with TiO 2 nanorods to obtain a heterostructure with improved photoelectrochemical (PEC) performance. TiO 2 nanorods were initially prepared using a hydrothermal method, and then MoS 2 nanosheets were synthesized using TiO 2 nanorods as the substrates. Various spectroscopic and microscopic methods were used to investigate the morphology and composition of the composite. Electrochemical impedance spectroscopy was also conducted to demonstrate the excellent electrical conductivity of the composite. The bioactivity of glucose oxidase (GOx) to glucose was validated with cyclic voltammetry in air-saturated solution. Finally, a PEC biosensor was fabricated by immobilizing GOx on MoS 2 nanosheet-TiO 2 nanorod composite modified ITO electrode. Owing to the high specific surface area, good conductivity, excellent biocompatibility and small band gap associated with this composite, the PEC glucose biosensor exhibited a dynamic range of 0.1–10.5 mM, sensitivity of 0.81 μA mM −1 , and a detection limit of 0.015 mM within the visible spectrum. [ABSTRACT FROM AUTHOR]

This study presents the synthesis and characterization of a novel glucose electrochemical biosensor based on gold nanoparticles/bovine serum albumin/Fe 3 O 4 (AuNPs/BSA/Fe 3 O 4 ) composite nanoparticles. The prepared magnetic composite nanoparticles consist of a BSA protein shell, providing biocompatible environment for enzyme immobilization. Furthermore, in situ immobilization of gold nanoparticles greatly enhances the performance of electron transfer. Using these composite nanoparticles, the model enzyme, glucose oxidase (GOx) was readily adsorbed to surface so as the GOx/AuNPs/BSA/Fe 3 O 4 electrochemical biosensor was developed. The electrochemical performance of the biosensor was characterized by cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS), and chronoamperometry. Under the optimal preparation conditions, the resultant biosensor has a short response time of 0.8 s, an excellent sensitivity of 115.3 μA mM −1 cm −2 , and a linear dynamic range from 0.25 to 7.0 mM with a low detection limit of 3.54 μM (S/N = 3). The high sensitivity, good reproducibility and stability of the biosensor presented in this study show that the as-prepared AuNPs/BSA/Fe 3 O 4 composite nanoparticles are a promising material for the development and construction of biosensors. [ABSTRACT FROM AUTHOR]

A simple, organic solvent free ultrasonic exfoliation method was developed to produce exfoliated SnS 2 nanoplates of an average size of 24 nm and thickness of 8 nm. These SnS 2 nanoplates were decorated onto the surfaces of multi-walled carbon nanotubes (MWCNT) to serve as the sensing electrode for glucose oxidase (GOx) based direct electron transfer sensing of glucose. The decoration of exfoliated SnS 2 nanoplates significantly improved hydrophilicity of the electrode and the electron transfer micro-environment between the redox-active site of GOx and the electrode surface, both beneficial to the direct electron transfer sensing of glucose. A high sensitivity of 28.9 μA/mM cm 2 was achieved, 1.77 times that of the SnS 2 -free case and among the highest reported for CNT and GOx based direct electrochemical glucose sensing. [ABSTRACT FROM AUTHOR]

We report on a small and simple graphene-based potentiometric sensor for the measurement of intracellular glucose concentration. A fine borosilicate glass capillary coated with graphene and subsequently immobilized with glucose oxidase (GOD) enzyme is inserted into the intracellular environment of a single human cell. The functional groups on the edge plane of graphene assist the attachment with the free amine terminals of GOD enzyme, resulting in a better immobilization. The sensor exhibits a glucose-dependent electrochemical potential against an Ag/AgCl reference microelectrode which is linear across the whole concentration range of interest (10 – 1000 μM). Glucose concentration in human fat cell measured by our graphene-based sensor is in good agreement with nuclear magnetic resonance (NMR) spectroscopy. [ABSTRACT FROM AUTHOR]

LiNbO 3 nanotubes are prepared by biotemplate-assisted synthetic route. The mesoporous LiNbO 3 nanotubes can be an ideal platform to immobilize glucose oxidase (GOx) for glucose biosensing. As the GOx-biocatalyzed oxidation of glucose yield H 2 O 2 , and LiNbO 3 can direct catalyze the generated H 2 O 2 . What's more, one dimensional channels will facilitate the diffusion of reactants and ensure adequate contact between glucose and enzymes. Thus the as-prepared biosensor exhibit high sensitivity (52.4 μA·mM −1 ·cm −2 ), fast response (<2 s) and excellent selectivity to glucose. The results suggest the potential implementation of LiNbO 3 as a sensing platform for electrochemical detection of biology reagents. [ABSTRACT FROM AUTHOR]

Abstract: Nanoporous gold (NPG) is composed of three-dimensional (3D) bicontinuous nanostructures with large surface area. Nano-channels inside NPG provide an ideal local environment for immobilization of enzyme molecules with expected stabilization of the protein molecules. In this work, glucose oxidase (GOx) has been brought to assemble on NPG via surface chemical reactions to form enzyme modified NPG nanomaterial with promising sensitivity for glucose detection. Cyclic voltammetry and single-potential step chronoamperometry (SPSC) are employed to study the electrochemical behavior of both bare and enzyme-modified NPG. Two redox mediators, p-benzoquinone (BQ) and ferrocenecarboxylic acid (FCA) are used to shuttle electrons between the enzyme redox center inside of GOx and the NPG electrode. Diffusion patterns at the functionalized NPG electrode are found significantly different from those on planar gold electrodes. This is mainly caused by internal 3D single crystal-like structures of NPG. Electrostatically neutral BQ mediator gives much higher voltammetric sensitivity than negatively charged FCA for GOx modified NPG electrodes.This study provides insight into the understanding of the intrinsic properties of NPG materials aiming at evolving enzymatic biosensors with high performance. [Copyright &y& Elsevier]

Highlights: [•] Graphene/nano-Au composite was synthesized by electrochemical co-reduction method in one step. [•] Glucose oxidase achieves direct electrochemistry on the graphene/nano-Au composite film. [•] The glucose biosensor shows a high sensitivity of 56.93μAmM−1 cm−2 toward glucose. [•] Glucose was detected with a wide linear range and low detection limit. [ABSTRACT FROM AUTHOR]

Abstract: Magnetic single-enzyme nanoparticles (MSENs) encapsulated within a composite Fe3O4/poly(pyrrole-N-propylsulfonic acid) network were successfully fabricated via the surface modification and in situ aqueous polymerization of separate enzyme molecules. The resulting MSENs with magnetism and conductivity exhibited high activity and stability. An amperometric glucose biosensor has been developed based on the modification of MSENs onto magnetic glassy carbon electrode (MGCE) through magnetism immobilization. The performance of the developed glucose biosensor was evaluated and the results indicated that a sensitive glucose biosensor could be fabricated. The obtained glucose biosensor presents high-selectivity monitoring of glucose, satisfactory stability, fast response time (4s), wide linear range (0.0005–3.5mM) and low detection limit (0.2μM). The analytical application of the glucose biosensor confirms the feasibility of glucose detection in serum sample. [Copyright &y& Elsevier]

• Surface-clean AuNPs/N-GQDs anchored on the P-MOF surface. • Enhanced electrochemical sensing and electrocatalytic abilities of H 2 O 2. • "Cascade nanoreactor" amplification for glucose detection. • Amperometric biosensor shows excellent anti-interference ability and sensitivity. • Glucose detection in serum samples under a low overpotential. Robust and efficient multimodal catalysis platforms that possess high catalytic activity and enhanced electrical conductivity are preferred for enhancing the electrical analysis performance under a low overpotential. This report describes a function-switchable amperometric sensor for electrochemical monitoring hydrogen peroxide and glucose under relatively low overpotential based on PEI-functionalized metal–organic framework (P-MOF) supported gold nanoparticles/nitrogen-doped graphene quantum dots (AuNPs/N-GQDs) and glucose oxidase. AuNPs/N-GQDs with high peroxidase mimicking activity was anchored on the P-MOF modified electrode surface as H 2 O 2 sensors, exhibiting a high sensitivity of 134.26 μA mM−1 cm−2 and a detection limit of 3.38 μM. Subsequently, AuNPs/N-GQDs-P-MOF used as a nanocarrier for glucose oxidase (GOx) to achieve "cascade nanoreactor" amplification for glucose detection. The amplified amperometric glucose biosensor showed excellent anti-interference ability, reproducibility, and a limit of detection as low as 0.7 μM (S/N = 3) with high sensitivity of 1512.4 μA mM−1 cm−2. In addition, the feasibility of the electrochemical biosensor for accurate and quantitative detection of glucose in human serum samples was confirmed with a recovery ranging from 93.2 to 99.3%. The strategy of combining AuNPs/N-GQDs-P-MOF and glucose oxidase for cascade catalysis in this work provides a simple yet efficient approach to prepare nanomaterial-based enzyme-mimics and enzymes hybrids with high performance, which holds great potential in biological and chemical applications of electrochemical devices and biosensing. [Display omitted] [ABSTRACT FROM AUTHOR]

Highlights: [•] A multilayered glucose biosensor with enhanced sensitivity was fabricated. [•] Combination of Ni2+/Ni3+ redox couple and glucose oxidase has been exploited for the first time. [•] Exhibits a lower detection limit of 100nM with a high sensitivity of 16,840μAmM−1 cm−2. [•] The surface shows a low Michaelis–Menten constant value of 2.4μM. [•] Detailed mechanism of sensing was proposed and justified. [ABSTRACT FROM AUTHOR]

Abstract: In this paper, the novel polyurethane-heparin nanoparticles (PU-Hep NPs) were synthesized and used to establish an amperometric glucose biosensor that can be applied in whole blood directly, which was based on the antibiofouling property of PU-Hep NPs. More details of preparation of PU-Hep NPs, immobilizing glucose oxidase (GOx) on (PU-Hep)/glass carbon electrode (GCE) and its electrochemical behavior in whole blood were presented. The cyclic voltammetric results indicated that GOx immobilized on the PU-Hep NPs exhibited direct electron transfer reaction, and the cyclic voltammogram (CV) displayed a pair of well-defined and nearly symmetric redox peaks with a formal potential of −408mV. The biosensor had good electrocatalytic activity toward glucose with a low detection limit 1.4×10−5 M in whole blood. The glucose biosensor did not respond to ascorbic acid (AA) and uric acid (UA) at their concentration normally encountered in blood. The development of materials science will bring a new momentum to electrical analysis. [Copyright &y& Elsevier]

Abstract: The carbon nitride dots (CNDs) can serve as an effective stabilizing agent for reduced graphene oxide (GO) prepared by chemical reduction using hydrazine hydrate as the reducing agent. Physicochemical characterization with a combination of techniques including UV–vis spectroscopy, Raman spectroscopy, X-ray diffraction and X-ray photoelectron spectroscopy indicate the preparation of aqueous dispersion of rGO and the formation of CNDs–rGO hybrids. We further demonstrate the subsequent self-assembly of the CNDs–rGO with glucose oxidase (GOD) into hybrids, which is confirmed by the scanning electron microscopy and electron energy dispersive spectrum analysis. As a typical application of such materials, a glucose biosensor has been constructed by deposition of the GOD–CNDs–rGO hybrids on the surface of a glassy carbon electrode. The linear detection range and detection limit are estimated to be from 40μM to 20mM (r =0.994) and 40μM at signal-to-noise ratio of 3, respectively. It is further shown that this glucose biosensor can be used for glucose detection in human blood serum. [Copyright &y& Elsevier]

Abstract: We have demonstrated the electrochemistry of a redox active species, Fe(CN)6 4−, flowing in a nitrocellulose membrane incorporated into two plates with a pole array and electrodes, and applied it by measuring the activity of an enzyme, glucose oxidase (GOx), captured by immunoreaction to develop an electrochemical immunochromatographic format. The flow in the membrane between the flat surfaces with electrodes is unstable because the solution seeps into the surfaces by capillary force and the substrate support and electrode materials have different wettabilities. Thus, electrochemical responses obtained were also unstable. We prepared the small pole array and incorporated a microelectrode in a pole to diminish the total contact area used to support the membrane. The solution flowed uniformly and stably in the membrane supported on the plates with the pole array, and a steady-state oxidation current of Fe(CN)6 4− was observed by amperometry. The mouse IgG used as a model target was captured in the antibody immobilization area prepared in the membrane. Subsequent flowing of GOx to conjugate the antibody allowed the labeling of the captured target by the formation of a sandwich-type immunocomplex. Fe(CN)6 4− produced through the enzyme reaction in the presence of glucose flowed downstream to give an electrochemical response with the electrode arranged 2mm from the antibody immobilization area. Electrochemical detection of redox species flowing in the membrane indicated the possibility for developing a single-step immunochromatographic assay format with electrochemical quantitation. [Copyright &y& Elsevier]

Abstract: The effect of the room temperature ionic liquid (1-butyl-2,3-dimethylimidazolium tetrafluoroborate ([BMMI][BF4])) on the immobilization of glucose oxidase (GOx) was studied. The electrochemical performance of biosensors prepared following different protocols indicated a beneficial effect of the ionic liquid on the analytical parameters. The chemical interaction between GOx, [BMMI][BF4] and glutaraldehyde was investigated using UV–visible spectroscopy (UV–vis) and circular dichroism (CD). Structural changes of the biomolecule were observed to depend on the method used for the immobilization. [Copyright &y& Elsevier]

Abstract: In glucose oxidase (GOx) based biosensors, O2 has been reported to compete with the artificial redox mediator for GOx electrons, decreasing the current density of the devices. Here, we investigate the effect of O2 on the redox mediator itself. To do so, a range of osmium-based redox polymers of different redox potentials has been investigated in non-physiological relevant conditions, i.e. under forced convection and under 1atm O2, to maximize the effect of the O2. We show that molecular O2 could be reduced on osmium complexes producing H2O2, a fraction of which could be further reduced to H2O on the same Os complexes. This reduction occurs on polymers with apparent redox potential E°′≤+0.07V vs. Ag/AgCl and the kinetic increases exponentially when E°′ decrease. In addition to the consequent loss of sensitivity and selectivity for a biosensor, or of power density and faradaic efficiency in the case of a biofuel cell, the H2O2 produced during the reduction of O2 on the Os complex may be deleterious for the enzyme. Our results suggest that the effect of O2 on the mediator itself may also be a parameter to be taken into account for the design of efficient redox mediators. [Copyright &y& Elsevier]

Abstract: Glucose oxidase (GOx) was stably immobilized via a simple physical adsorption method onto the nanostructured Au thin films fabricated by using electrodeposition and galvanic replacement technology, which provides a facile method to prepare morphology-controllable Au films and also facilitates the preparation and application of enzyme modified electrodes. An obvious advantage of the as-prepared enzyme electrode (denoted as GOx/Au/GCE) is that the nano-Au films provide a favorable microenvironment for GOx and facilitate the electron transfer between the active center of GOx and electrodes. Cyclic voltammetry (CV) results indicate that the immobilized GOx displayed a direct, reversible and surface-confined redox reaction in the phosphate buffer solution. Furthermore, the enzyme modified electrode was used as a glucose bioelectrochemical sensor, exhibiting a linear relationship in the concentration ranges of 2.5–32.5μmolL−1 and 60–130μmolL−1 with a detection limit of 0.32μmolL−1 (S/N=3) at an applied potential of −0.55V. Due to the excellent stability, sensitivity and anti-interference ability, the Au thin films are hopeful in the construction of glucose biosensors. [Copyright &y& Elsevier]

Abstract: We report an enzyme-modified nanoporous gold (NPG) biosensor with excellent sensitivity and selectivity towards the detection of glucose in the physiological environment containing common interferents. The internal surface of biocompatible NPG films is functionalized with glucose oxidase using thiols as linking molecules. The three-dimensional porous metal/organic hybrid electrode exhibits effective enzyme immobilization and peroxide detection on gold ligaments for amperometric glucose sensing. This study has important implications in developing NPG based metal/organic electrodes for electrochemical sensors with high selectivity and sensitivity. [Copyright &y& Elsevier]