Inhibition and enhancement of glucose oxidase activity in a chitosan-based electrode filled with silver nanoparticles

A chitosan-based electrode filled with silver nanoparticles (AgNPs) and glucose oxidase (GOD) was used as an enzyme electrode to investigate the effect of aging process of AgNPs on the GOD activity. Freshly prepared AgNPs inhibit the GOD activity, however, the inhibitory effect decreased with the increase of aging time. After aged for a period of time, AgNPs showed enhancement effect on the GOD activity. The effect of aging was studied by the measurements of Ag⁺ ions concentration, zeta (ζ) potential and X-ray photoelectron spectroscopy (XPS). And the results indicated that the concentration of Ag⁺ ions in the silver sol decreased during the aging period (i.e. Ag⁺ ions converted to more inert silver metal Ag⁰). The effect of AgNPs on the GOD activity can be changed by controlling the aging time of AgNPs. This research provides a new and simple approach to mediate AgNPs property, which is of great value in potential application of AgNPs in biosensors and nanoscale devices.     

Tin disulfide nanoflakes decorated with gold nanoparticles for direct electrochemistry of glucose oxidase and glucose biosensing

Previously, we have prepared nanoflake-like tin disulfide (SnS2) and used for the immobilization of proteins and biosensing. We have now modified an electrode with a composite consisting of nanoflake-like SnS2 decorated with gold nanoparticles (Au-NPs) and have immobilized glucose oxidase (GOx) on its surface in order to study its direct electrochemistry. Scanning electron microscopy, electrochemical impedance spectroscopy, Fourier transform IR spectroscopy and cyclic voltammetry were used to examine the interaction between GOx and the AuNP-SnS2 film. It is shown that the composite film has a larger surface area and offers a microenvironment that facilitates the direct electron transfer between enzyme and electrode surface. The immobilized enzyme retains its bioactivity and undergoes a surface-controlled, reversible 2-proton and 2-electron transfer reaction, with an apparent electron transfer rate constant of 3.87 s ^-1. Compared to the nanoflake-like SnS2-based glucose sensor, the GOx-based biosensor exhibits a lower detection limit (1.0 :M), a better sensitivity (21.8 mA?M ^-1 ?cm ^-2), and a wider linear range (from 0.02 to 1.3 mM). The sensor displays excellent selectivity, good reproducibility, and acceptable stability. It was successfully applied to reagentless sensing of glucose at ?0.43 V.

Glucose biosensor based on the layer-by-layer self-assembling of glucose oxidase and chitosan derivatives on a thiolated gold surface

This work examines in deep the analytical performance of an example of “first-generation” microdevices: capillary electrophoresis microchip (CE) with end-channel electrochemical detection (ED). A hydroquinone and arbutin separation strategically chosen as route involving pharmaceutical-clinical testing, public safety and food control scenes was carried out. The reproducibility of the unpinched electrokinetic protocol was carefully studied and the technical possibility of working indiscriminately and/or sequentially with both simple cross-injectors was also demonstrated using a real sample (R.S.D.'s less than 7%). The robustness of the injection protocol allowed checking the state of the microchip/detector coupling and following the extraction efficiency of the analyte from real sample. Separation variables such as pH, ionic strength and, separation voltage were also carefully assayed and optimized. Analyte screening was performed using borate buffer (pH 9, 60 mM) in less than 180 s in the samples studied improving dramatically the analysis times used for the same analytes on a conventional scale (15 min), with good precision (R.S.D.'s ranging 5-10%), accuracy (recoveries ranging 90-110%) and acceptable resolution (Rs ≥ 1.0).In addition, the excellent analytical performance of the overall analytical method indicated the quality of the whole analytical microsystem and allowed to introduce the definition of robustness for methodologies developed into the “lab-on-a-chip” scene.     

A glucose biosensor based on electrodeposited biocomposites of gold nanoparticles and glucose oxidase enzyme.

Electrodeposition was used for the codeposition of glucose oxidase enzyme and a gold nanoparticle-silicate network onto an indium tin oxide (ITO) glass electrode. This co-entrapment of glucose oxidase enzyme in a gold nanoparticle-silicate network imparts biocatalytic activity to the film. The gold nanoparticles in the network catalyse the oxidation and reduction of H2O2, the by-product of the enzymatic reaction. The low operating potential of the sensor eliminates the interference from common interferents, such as acetaminophen, ascorbic acid, dopamine, etc.     

Covalent attachment of glucose oxidase to an Au electrode modified with gold nanoparticles for use as glucose biosensor

A feasible method to fabricate glucose biosensor was developed by covalent attachment of glucose oxidase (GOx) to a gold nanoparticle monolayer modified Au electrode. Cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS) of ferrocyanide followed and confirmed the assemble process of biosensor, and indicated that the gold nanoparticles in the biosensing interface efficiently improved the electron transfer between analyte and electrode surface. CV performed in the presence of excess glucose and artificial redox mediator, ferrocenemethanol, allowed to quantify the surface concentration of electrically wired enzyme (Gamma(E)(0)) on the basis of kinetic models reported in literature. The Gamma(E)(0) on proposed electrode was high to 4.1 x 10(-12) mol.cm(-2), which was more than four times of that on electrode direct immobilization of enzyme by cystamine without intermediate layer of gold nanoparticles and 2.4 times of a saturated monolayer of GOx on electrode surface. The analytical performance of this biosensor was investigated by amperometry. The sensor provided a linear response to glucose over the concentration range of 2.0 x 10(-5)-5.7 x 10(-3) M with a sensitivity of 8.8 microA.mM(-1).cm(-2) and a detection limit of 8.2 microM. The apparent Michaelis-Menten constant (K(m)(app)) for the sensor was found to be 4.3 mM. In addition, the sensor has good reproducibility, and can remain stable over 30 days.     

Activity enhancement of a screen-printed carbon electrode by modification with gold nanoparticles for glucose determination

We have successfully developed a highly sensitive electrochemical sensor strip for a home blood-sugar monitoring device by a single-step straightforward procedure. The strip consists of a pair of screen-printed carbon electrodes, which work as counter and working electrodes in the chronoamperometric mode. To remedy the poor electrochemical activity of the printed carbon electrode, a small amount of gold nanoparticles was immobilized on the electrode. In the presence of glucose oxidase, the electrode modified with 2-nm particles showed about a five times higher sensitivity for glucose oxidation than the bare printed carbon electrode, and there was a significant dependence of the current on the particle diameter. Based on these observations, we have elucidated the glucose oxidation mechanism, which is comprised of two key factors, i.e. (1) electron transfer between the gold particles, and (2) electronic coupling between the gold particles and glucose oxidase.     

Arrays of covalently bonded single gold nanoparticles on thiolated molecular assemblies

A simple approach to form arrays of covalently bonded single gold nanoparticles (AuNPs) is demonstrated. Asymmetric molecular assemblies composed of two layers of rigid aromatic molecules with different structures, arranged in hexagonal arrays on a template produced by edge-spreading lithography, are used to guide the assembly of AuNPs. Arrays of single AuNPs are achieved by taking advantage of the interplay of electrostatic interactions and covalent bonding in conjunction with the positional constraint on the template. Schiff base chemistry is highlighted in the surface chemical reaction to selectively modify nanoscale surface features with high yield.     

Novel glucose biosensor based on a glassy carbon electrode modified with hollow gold nanoparticles and glucose oxidase

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.

Glucose biosensor based on graphite electrodes modified with glucose oxidase and colloidal gold nanoparticles

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 τ_1/2 of V _max 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.     

Effect of silica nanoparticles with different sizes on the catalytic activity of glucose oxidase

In this work we present a strategy for the covalent immobilization of periodate oxidized glucose oxidase () to aminated silica nanoparticles (ASNPs) modified on gold electrodes. Silica nanoparticles greatly enhanced the catalytic ability of GOx toward the oxidation of glucose and improved the electron transfer between the GOx and the electrode surface. ASNPs of varying size—that is 100, 80, 60, and 30 nm—were prepared, and they were used to fabricate biosensors. Electrochemical impedance spectroscopy (EIS) of ferrocyanide followed the assembly process and verified the successful immobilization of on ASNPs modified on gold electrodes. From the analysis of catalytic signals of biosensors using different sizes of ASNPs under the same conditions, the surface concentration of electrically wired enzyme (Γ _ET) was estimated and was found to increase with decreasing ASNPs size. Therefore, the sensitivity of biosensors using smaller ASNPs was higher than that using larger particles. Specifically, we utilized the ASNPs with optimal size (30 nm) to fabricate the glucose biosensor. The resulting electrodes showed a wide linear response to glucose at least to 6 mM and reached 95% of the steady-state current in less than 4 s with a sensitivity of 5.02 μA mM⁻¹ cm⁻² and a detection limit of 0.01 mM. The biosensor also showed excellent stability and good reproducibility. Electronic supplementary material Supplementary material is available in the online version of this article at and is accessible for authorized users.     

Engineering the interface between glucose oxidase and nanoparticles

The behavior of glucose oxidase (GOx) on gold nanoparticles (NPs) was investigated as a function of (1) NP surface chemistry, (2) stabilizing protein additives, and (3) protein microenvironment. GOx secondary structure and unfolding was probed by circular dichroism (CD) spectroscopy and fluorescence, and GOx enzymatic activity was measured by a colorimetric assay. We also examined the activity and structure of GOx after displacement from the NP surface. Generally, GOx behavior was negatively impacted by conjugation to the NP, and conjugation conditions could vary the influence of the NP. Surface chemistry and protein microenvironment could improve behavior, but addition of stabilizing proteins negatively influenced activity. After displacement from the NPs, GOx tended to remain unfolded, indicating that the interactions with the NP were irreversible.     

Glucose biosensor based on a platinum electrode modified with rhodium nanoparticles and with glucose oxidase immobilized on gold nanoparticles

We have developed an enzymatic glucose biosensor that is based on a flat platinum electrode which was covered with electrophoretically deposited rhodium (Rh) nanoparticles and then sintered to form a large surface area. The biosensor was obtained by depositing glucose oxidase (GOx), Nafion, and gold nanoparticles (AuNPs) on the Rh electrode. The electrical potential and the fractions of Nafion and GOx were optimized. The resulting biosensor has a very high sensitivity (68.1 μA mM^?1 cm^?2) and good linearity in the range from 0.05 to 15 mM (r?=?0.989). The limit of detection is as low as 0.03 mM (at an SNR of 3). The glucose biosensor also is quite selective and is not interfered by electroactive substances including ascorbic acid, uric acid and acetaminophen. The lifespan is up to 90 days. It was applied to the determination of glucose in blood serum, and the results compare very well with those obtained with a clinical analyzer.

Application of nanoparticles for the enhancement of latent fingerprints

Two different types of nanoparticles dissolved in organic solution, gold stabilized by n-alkanethiols and CdSe/ZnS stabilized by n-alkane-amine, adhere preferentially to the ridges of latent fingerprints; the gold deposits catalyze silver electroless deposition from "Silver Physical Developer" (Ag-PD), an aqueous solution containing silver colloids stabilized by cationic surfactants, to form dark impressions of the ridge details; the hydrophobic capped gold nanoparticles significantly improve the intensity and clarity of the developed prints compared with Ag-PD alone; finger marks treated with CdSe/ZnS nanoparticles can be viewed directly, due to their fluorescence under UV illumination.     

Selective enhancement of nucleases by polyvalent DNA-functionalized gold nanoparticles

We demonstrate that polyvalent DNA-functionalized gold nanoparticles (DNA-Au NPs) selectively enhance ribonuclease H (RNase H) activity while inhibiting most biologically relevant nucleases. This combination of properties is particularly interesting in the context of gene regulation, since high RNase H activity results in rapid mRNA degradation and general nuclease inhibition results in high biological stability. We have investigated the mechanism of selective RNase H activation and found that the high DNA density of DNA-Au NPs is responsible for this unusual behavior. This work adds to our understanding of polyvalent DNA-Au NPs as gene regulation agents and suggests a new model for selectively controlling protein-nanoparticle interactions.     

A novel enhancement assay for immunochromatographic test strips using gold nanoparticles

The immunochromatographic assay is a well-known and convenient diagnostic system. In this report, the development of a novel enhancement assay for the test strips is described. Additionally, this highly sensitive immunochromatographic assay was applied to detect human chorionic gonadotropin hormone (HCG) as the model case. The primary antibody-conjugated gold nanoparticles were used as the enhancer of the standard method. The primary antibodies were immobilized within a defined detection zone (test line) on the diagnostic nitrocellulose membrane. The secondary antibodies were conjugated with colloidal gold nanoparticles. In combination with an effective sample pretreatment, the gold-conjugated antibodies and the primary antibodies formed a sandwich complex with the target protein. Within the test line, the sandwich complex was immobilized, and furthermore, concentrated by the enhancer resulting in a localized surface plasmon resonance (LSPR) phenomenon and a distinct red color on the test line. The intensity of color of the red test line (signal intensity), which correlated directly with the concentration of the target protein in the standard or spiked samples, was assessed visually and by computer image analysis using a three-determination analysis. Under optimum conditions, the limit of detection (LOD) for HCG assay was 1 pg/mL. When using human serum, 10 pg/mL of HCG could be detected. We have also spiked total prostate-specific antigen (TPSA) in female serum. The LOD for TPSA was determined as 0.2 ng/mL. With this method, the quantitative determination of the target protein could be completed in less than 15 min. Our novel immunochromatographic strips using the enhancing method based on LSPR of gold nanoparticles are useful as a rapid and simple screening method for the detection of important analytes for medical applications, environmental monitoring, food control, and biosecurity.      

Integration of a highly ordered gold nanowires array with glucose oxidase for ultra-sensitive glucose detection

A highly sensitive amperometric nanobiosensor has been developed by integration of glucose oxidase (GO_x) with a gold nanowires array (AuNWA) by cross-linking with a mixture of glutaraldehyde (GLA) and bovine serum albumin (BSA). An initial investigation of the morphology of the synthesized AuNWA by field emission scanning electron microscopy (FESEM) and field emission transmission electron microscopy (FETEM) revealed that the nanowires array was highly ordered with rough surface, and the electrochemical features of the AuNWA with/without modification were also investigated. The integrated AuNWA–BSA–GLA–GO_x nanobiosensor with Nafion membrane gave a very high sensitivity of 298.2 μA cm⁻² mM⁻¹ for amperometric detection of glucose, while also achieving a low detection limit of 0.1 μM, and a wide linear range of 5–6000 μM. Furthermore, the nanobiosensor exhibited excellent anti-interference ability towards uric acid (UA) and ascorbic acid (AA) with the aid of Nafion membrane, and the results obtained for the analysis of human blood serum indicated that the device is capable of glucose detection in real samples.     

Platinum covering of gold nanoparticles for utilization enhancement of Pt in electrocatalysts

This work attempts to enhance platinum utilization in a Pt-based electrocatalyst by the tuned covering of gold nanoparticles with small Pt entities. Reductive deposition of Pt on Au nanoparticles of two size ranges (Au-I: 10 +/- 1.2 nm, Au-II: 3 +/- 0.6 nm) up to different atomic Pt : Au ratios (m) was used to prepare two series of samples named Pt(m)insertion markAu-I and Pt(m)insertion markAu-II particles, respectively. The obtained Pt(m)insertion markAu particles were characterized with TEM, XPS, UV-Vis and XRD techniques, and then loaded on conventional Vulcan XC-72 carbon to make Pt(m)insertion markAu/C electrocatalysts. Cyclic voltammetry (CV) measurements showed that the electrochemical active surface area (EAS) and Pt utilization (U(Pt)) in Pt(m)insertion markAu/C were enhanced remarkably at m< or = 0.2 for Pt(m)insertion markAu-I/C or m< or = 0.5 for Pt(m)insertion markAu-II/C, in comparison to conventional Pt/C electrocatalyst. In particular, U(Pt) was enhanced to nearly 100% in Pt(m)insertion markAu-I/C catalysts at m< or = 0.05 and in Pt(m)insertion markAu-II/C at m< or = 0.1. In the CV measurement of methanol electro-oxidation, the specific mass activity of Pt in Pt(m)insertion markAu/C catalysts was found in proportional to U(Pt), confirming that the enhancement of Pt utilization is essential for the development of highly active Pt-based electrocatalysts. The highly dispersed Pt entities on Au nanoparticles proved to be stable during the electro-oxidation of methanol. Our study also showed that the use of smaller Au nanoparticles is advantageous for the generation of more active Pt catalyst at higher atomic Pt : Au ratios.     

Interfacial activity of polymer-coated gold nanoparticles

A systematic study of the interfacial activity of polymer-coated gold nanoparticles was performed with the use of a computer-controlled four-roll mill. The nanoparticle locality within the polymeric domains (bulk or interface) was controlled by means of a mixture of polymeric ligands grafted to the gold nanoparticle core. The bulk polymers were polybutadiene (PBd) and polydimethylsiloxane (PDMS). Monoterminated PDMS and PBd ligands were synthesized on the basis of the esterification of reactive groups (such as hydroxyl or amino groups) with lipoic acid anhydride. The formation of polymer-coated nanoparticles using these lipoic acid-functionalized polymers was confirmed via transmission electron microscopy (TEM), and their interfacial activity was manifested as a reduction of the interfacial tension and in the enhanced stability of thin films (as seen via the inhibition of coalescence). The nanoparticles showed an equal, if not superior, ability to reduce the interfacial tension when compared to previous studies on the effect of insoluble surfactants; however, these particles proved not to be as effective at inhibiting coalescence as their surfactant counterpart. We suggest that this effect may be caused by an increase in the attractive van der Waals forces created by the presence of metal-core nanoparticles. Experimental measurements using the four-roll mill allow us to explore the relationship between nanoparticle concentration at the interface and interfacial tension. In particular, we have found evidence that the interface concentration can be increased relative to the equilibrium value achieved by diffusion alone, and thus the interfacial tension can be systematically reduced if the interfacial area is increased temporarily via drop deformation or breakup followed by recoalescence.     

Direct electrochemistry of glucose oxidase and a biosensor for glucose based on a glass carbon electrode modified with MoS2 nanosheets decorated with gold nanoparticles

An electrochemical glucose biosensor was developed by immobilizing glucose oxidase (GOx) on a glass carbon electrode that was modified with molybdenum disulfide (MoS₂) nanosheets that were decorated with gold nanoparticles (AuNPs). The electrochemical performance of the modified electrode was investigated by cyclic voltammetry, and it is found that use of the AuNPs-decorated MoS₂ nanocomposite accelerates the electron transfer from electrode to the immobilized enzyme. This enables the direct electrochemistry of GOx without any electron mediator. The synergistic effect the MoS₂ nanosheets and the AuNPs result in excellent electrocatalytic activity. Glucose can be detected in the concentration range from 10 to 300 μM, and down to levels as low as 2.8 μM. The biosensor also displays good reproducibility and long-term stability, suggesting that it represents a promising tool for biological assays. Figure

A MoS₂-based glucose sensor has been prepared by gold nanoparticles-decorated MoS₂ nanocomposite, which exhibited excellent electrocatalytic activity, reproducibility and long-term stability. It was applied to determine glucose concentration in human serum, suggest the sensor maybe promising for practical application.