Hydrogen bubble dynamic template synthesis of porous gold for nonenzymatic electrochemical detection of glucose

Schottky Interface Enabled Electrospun Rhodium Oxide Doped Gold for Both pH Sensing and Glucose Measurements in Neutral Buffer and Human Serum

This study has focused on adjusting sensing environment from basic to neutral pH and improve sensing performance by doping electrodeposited gold (Au) with metal oxide for nonenzymatic glucose measurements in forming a Schottky interface for superior glucose sensing with detailed analysis for the sensing mechanism. The prepared sensor also holds the ability to measure pH with the identical electrospun metal oxide-electrodeposited Au, which composed a dual sensor (glucose and pH sensor) through applying chronoamperometry and open circuit potential methods. The rhodium oxide nanocoral structure was fabricated with an electrospinning precursor solution, followed by a calcination process, and it was mixed with electrodeposited nanocoral gold to form the Schottky interface by constructing a p-n type heterogeneous junction for improved sensitivity in glucose detection. The prepared materials were characterized by X-ray powder diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), and X-ray photoelectron spectrometry (XPS), etc. The prepared materials were used for both pH responsive testing and amperometric glucose measurements. The rhodium oxide nanocoral doped gold demonstrated a sensitivity of 3.52 μA mM-1 cm-2 and limit of detection of 20 μM with linear range up to 3 mM glucose concentration compared to solely electrodeposited gold for a sensitivity of 0.46 μA mM-1 cm-2 and a limit of detection of 450 μM. The Mott-Schottky method was used for the analysis of an electron transfer process from noble metal to metal oxide to electrolyte in demonstrating the improved sensitivity at neutral pH for glucose measurements due to the Schottky barrier adjustment mechanism at an applied flat band potential of 0.3 V. This work opens a new venue in illustrating the metal oxide/metal materials in the glucose neutral response mechanism. In the end, human serum samples were tested against current commercial glucose meter to certify the accuracy of the proposed sensor.

The application of a novel biomimetic enzyme p-BEs cascade catalytic platform for the rapid detection of glucose

The blood glucose concentration in aquatic organisms, a crucial indicator reflecting their health status, holds significant importance for detecting glucose levels in serum in terms of processing and quality monitoring. In this study, a novel POD biomimetic enzyme (p-BEs) with horseradish peroxidase catalytic properties was designed, optimized, and its mechanism was discussed in detail. Based on this, a portable system has been developed capable of determining glucose levels in three ways: quantitatively analyzed through UV-Vis/MD, quantitatively analyzed on-site using a mobile phone RGB, and semi-quantitatively analyzed through a drip plate. Meanwhile, compared with other catalytic methods for detecting glucose, we achieved a lower limit of detection (0.03 μM) and shorter detection time (12 min), with high catalytic activity. This study provides new insights into the design of efficient and reliable cascade catalytic systems responsive to glucose, offering a low-cost, simplicity of operation method for glucose detection.

A hybrid effective medium description for nanoporous gold films and thickness-mediated control of optical absorption

With the increasing demand for sensing platforms operating across UV, visible, and near-infrared wavelengths, nanoporous gold has emerged as an ideal substrate for rapid, quantitative detection of analytes with excellent specificity and high sensitivity. This study investigates thickness-mediated compositional changes and their impact on scattering characteristics of thin nanoporous gold films fabricated using selective chemical etching. Specifically, we observe thickness-induced morphological and structural changes across different fabricated samples from 25 to 100 nm in thickness. Upon their optical characterization across UV-VIS-NIR spectral regime, we notice that the constitutional differences among samples manifest distinctively & deterministically in their total optical scattering response. In order to gain insights into these observed scattering responses and to fathom the subtle connections between structural properties of NPG films and their optical response, a hybrid theoretical model comprising Maxwell-Garnett & Bruggeman effective medium approximations has been adopted. Our approach not only allows to appropriately account for the inhomogeneous nature of these films, but also corroborates well with the atomic force microscopy characterizations of the fabricated samples. Furthermore, tracing such a theoretical model is important as it helps in systematically ascertaining additional loss terms emerging in the complex dielectric function of films due to their nanoscale porosity & roughness, permitting a good reproduction of measured optical spectra. We believe, our approach will not only facilitate accurate regulation of losses in NPG thin films but will also aid in deriving customized optical performance from them, thereby advancing their potential applications in sensing and beyond.

Reagentless Glucose Biosensor Based on Combination of Platinum Nanostructures and Polypyrrole Layer

Two types of low-cost reagentless electrochemical glucose biosensors based on graphite rod (GR) electrodes were developed. The electrodes modified with electrochemically synthesized platinum nanostructures (PtNS), 1,10-phenanthroline-5,6-dione (PD), glucose oxidase (GOx) without and with a polypyrrole (Ppy) layer-(i) GR/PtNS/PD/GOx and (ii) GR/PtNS/PD/GOx/Ppy, respectively, were prepared and tested. Glucose biosensors based on GR/PtNS/PD/GOx and GR/PtNS/PD/GOx/Ppy electrodes were characterized by the sensitivity of 10.1 and 5.31 μA/(mM cm2), linear range (LR) up to 16.5 and 39.0 mM, limit of detection (LOD) of 0.198 and 0.561 mM, good reproducibility, and storage stability. The developed glucose biosensors based on GR/PtNS/PD/GOx/Ppy electrodes showed exceptional resistance to interfering compounds and proved to be highly efficient for the determination of glucose levels in blood serum.

The Development and Evaluation of Reagentless Glucose Biosensors Using Dendritic Gold Nanostructures as a Promising Sensing Platform

Reagentless electrochemical glucose biosensors were developed and investigated. A graphite rod (GR) electrode modified with electrochemically synthesized dendritic gold nanostructures (DGNs) and redox mediators (Med) such as ferrocenecarboxylic acid (FCA), 1,10-phenathroline-5,6-dione (PD), N,N,N',N'-tetramethylbenzidine (TMB) or tetrathiafulvalene (TTF) in combination with glucose oxidase (GOx) (GR/DGNs/FCA/GOx, GR/DGNs/PD/GOx, GR/DGNs/TMB/GOx, or GR/DGNs/TTF/GOx) were developed and electrochemically investigated. A biosensor based on threefold-layer-by-layer-deposited PD and GOx (GR/DGNs/(PD/GOx)₃) was found to be the most suitable for the determination of glucose. To improve the performance of the developed biosensor, the surface of the GR/DGNs/(PD/GOx)₃ electrode was modified with polypyrrole (Ppy) for 5 h. A glucose biosensor based on a GR/DGNs/(PD/GOx)₃/Ppy_{(5 h)} electrode was characterized using a wide linear dynamic range of up to 39.0 mmol L^-1 of glucose, sensitivity of 3.03 µA mM^-1 cm^-2, limit of detection of 0.683 mmol L^-1, and repeatability of 9.03% for a 29.4 mmol L^-1 glucose concentration. The Ppy-based glucose biosensor was characterized by a good storage stability (τ_1/2 = 9.0 days). Additionally, the performance of the developed biosensor in blood serum was investigated.

Feather-like Gold Nanostructures Anchored onto 3D Mesoporous Laser-Scribed Graphene: A Highly Sensitive Platform for Enzymeless Glucose Electrochemical Detection in Neutral Media

The authors present a novel sensing platform for a disposable electrochemical, non-enzymatic glucose sensor strip at physiological pH. The sensing material is based on dendritic gold nanostructures (AuNs) resembling feather branches, which are electrodeposited onto a laser-scribed 3D graphene electrode (LSGE). The LSGEs were fabricated via a one-step laser scribing process on a commercially available polyimide sheet. This study investigates several parameters that influence the morphology of the deposited Au nanostructures and the catalytic activity toward glucose electro-oxidation. The electrocatalytic activity of the AuNs-LSGE was evaluated using cyclic voltammetry (CV), linear sweep voltammetry (LSV), and amperometry and was compared to commercially available carbon electrodes prepared under the same electrodeposition conditions. The sensor demonstrated good stability and high selectivity of the amperometric response in the presence of interfering agents, such as ascorbic acid, when a Nafion membrane was applied over the electrode surface. The proposed sensing strategy offers a wide linear detection range, from 0.5 to 20 mM, which covers normal and elevated levels of glucose in the blood, with a detection limit of 0.21 mM. The AuNs-LSGE platform exhibits great potential for use as a disposable glucose sensor strip for point-of-care applications, including self-monitoring and food management. Its non-enzymatic features reduce dependence on enzymes, making it suitable for practical and cost-effective biosensing solutions.

Field Effect Transistor with Nanoporous Gold Electrode

Nanoporous gold (NPG) has excellent catalytic activity and has been used in the recent literature on this issue as a sensor in various electrochemical and bioelectrochemical reactions. This paper reports on a new type of metal-oxide-semiconductor field-effect transistor (MOSFET) that utilizes NPG as a gate electrode. Both n-channel and p-channel MOSFETs with NPG gate electrodes have been fabricated. The MOSFETs can be used as sensors and the results of two experiments are reported: the detection of glucose and the detection of carbon monoxide. A detailed comparison of the performance of the new MOSFET to that of the older generation of MOSFETs fitted with zinc oxide gate electrodes is given.

Facile fabrication of hierarchically nanostructured gold electrode for bio-electrochemical applications

Nanoporous gold (NPG) is one of the most extensively investigated nanomaterials owing to its tunable pore size, ease of surface modification, and range of applications from catalysis, actuation, and molecular release to the development of electrochemical sensors. In an effort to improve the usefulness of NPG, a simple and robust method for the fabrication of hierarchical and bimodal nanoporous gold electrodes (hb-NPG) containing both macro-and mesopores is reported using electrochemical alloying and dealloying processes to engineer a bicontinuous solid/void morphology. Scanning electron microscopy (color SEM) images depict the hierarchical pore structure created after the multistep synthesis with an ensemble of tiny pores below 100 nm in size located in ligaments spanning larger pores of several hundred nanometers. Smaller-sized pores are exploited for surface modification, and the network of larger pores aids in molecular transport. Cyclic voltammetry (CV) was used to compare the electrochemically active surface area of the hierarchical bimodal structure with that of the regular unimodal NPG with an emphasis on the critical role of both dealloying and annealing in creating the desired structure. The adsorption of different proteins was followed using UV-vis absorbance measurements of solution depletion revealing the high loading capacity of hb-NPG. The surface coverage of lipoic acid on the hb-NPG was analyzed using thermogravimetric analysis (TGA) and reductive desorption. The roughness factor determinations suggest that the fabricated hb-NPG electrode has tremendous potential for biosensor development by changing the scaling relations between volume and surface area which may lead to improved analytical performance. We have chosen to take advantage of the surface architectures of hb-NPG due to the presence of a large specific surface area for functionalization and rapid transport pathways for faster response. It is shown that the hb-NPG electrode has a higher sensitivity for the amperometric detection of glucose than does an NPG electrode of the same geometric surface area.

3D-Structured Au(NiMo)/Ti Catalysts for the Electrooxidation of Glucose

In this study, 3D-structured NiMo coatings have been constructed via the widely used electrodeposition method on a Ti surface and decorated with very small Au crystallites by galvanic displacement (Au(NiMo)/Ti). The catalysts have been characterized using scanning electron microscopy, energy dispersive X-ray analysis, and inductively coupled plasma optical emission spectroscopy. Different Au(NiMo)/Ti catalysts, which had Au loadings of 1.8, 2.3, and 3.9 µgAu cm−2, were prepared. The electrocatalytic activity of the Au(NiMo)/Ti catalysts was examined with respect to the oxidation of glucose in alkaline media by cyclic voltammetry. It was found that the Au(NiMo)/Ti catalysts with Au loadings in the range of 1.8 up to 3.9 µgAu cm−2 had a higher activity compared to that of NiMo/Ti. A direct glucose-hydrogen peroxide (C6H12O6-H2O2) single fuel cell was constructed with the different Au-loading-containing Au(NiMo)/Ti catalysts as the anode and Pt as the cathode. The fuel cells exhibited an open circuit voltage of ca. 1.0 V and peak power densities up to 8.75 mW cm−2 at 25 °C. The highest specific peak power densities of 2.24 mW µgAu−1 at 25 °C were attained using the Au(NiMo)/Ti catalyst with the Au loading of 3.9 µg cm−2 as the anode.

A Label-Free Colorimetric Assay Based on Gold Nanoparticles for the Detection of H2O2 and Glucose

The significance of sensing hydrogen peroxide (H2O2) is due to its ubiquity, being a potential biomarker as well as an end-product of several oxidation reactions. Herein, based on gold nanoparticles (AuNPs) and coupled with single-stranded DNA (ssDNA) and ceria nanoparticles (CeO2), we developed a novel colorimetric method to detect H2O2 and glucose in NaCl solutions. In the presence of H2O2, ssDNA adsorbed on the surface of CeO2 could be released and subsequently decorated AuNPs, resulting in a distinct color change of the aqueous solution from purple to red, which could be observed by the naked eye. Since H2O2 can be produced in the process of glucose oxidation by glucose oxidase (GOx), this approach can also be employed to detect glucose. By employing this sensing system, the detection limits for H2O2 and glucose are about 0.21 μM and 3.01 µM, respectively. Additionally, monitoring the content of glucose in blood serum samples was successfully achieved by the proposed strategy. This work opens a potential avenue for the quantitative detection of H2O2 and glucose in clinical diagnostics.

A sensitive, fast, selective, and reusable enzyme-free glucose sensor based on monodisperse AuNi alloy nanoparticles on activated carbon support

In this study, a glucose sensor modified with activated carbon supported gold-nickel (AuNi@AC) metal nanoparticles was prepared for the early diagnosis of diabetes. Electrochemical tests were carried out by determining the optimum working conditions of the prepared glucose sensor. The characterization analyses of the designed glucose sensor were performed by Transmission Electron Microscopy (TEM), X-Ray Diffraction (XRD), X-Ray Photoelectron Spectroscopy (XPS) and Raman Spectroscopy. It was determined that the average particle size of the nanoparticles in the AuNi alloy structure was 2.03 ± 0.37 nm. The determined detection limit of the AuNi@AC nanosensor was calculated as 0.41 μM as a result of the high linear range provided up to 1.7 mM. In addition, the sensitivity of AuNi@AC nanosensor to glucose, which has a high sensitivity value of 1955 μA mM^-1 cm^-2, was determined.

Improving Nonenzymatic Biosensing Performance of Electrospun Carbon Nanofibers decorated with Ni/Co Particles via Oxidation

Nonenzymatic biosensors do not require enzyme immobilization nor face degradation problem. Hence, nonenzymatic biosensors have recently attracted growing attention due to the stability and reproducibility. Here, a comparative study was conducted to quantitatively evaluate the glucose sensing of pure/oxidized Ni, Co, and their bimetal nanostructures grown on electrospun carbon nanofibers (ECNFs) to provide a low-cost free-standing electrode. The prepared nanostructures exhibited sensitivity (from 66.28 to 610.6 μA mM^-1 cm^-2), linear range of 2-10 mM, limit of detection in the range of 1 mM, and the response time (< 5 s), besides outstanding selectivity and applicability for glucose detection in the human serum. Moreover, the oxidizable interfering species, such as ascorbic acid (AA), uric acid (UA), and dopamine (DA), did not cause interference. Co-C and Ni-C phase diagrams, solid-state diffusion phenomena, and rearrangement of dissolved C atoms after migration from metal particles were discussed. This study undoubtedly provides new prospects on the nonenzymatic biosensing performance of mono-metal, bimetal, and oxide compounds of Ni and Co elements, which could be quite helpful for the fabrication of biomolecules detecting devices.

Rapid, multiplexed, and nucleic acid amplification-free detection of SARS-CoV-2 RNA using an electrochemical biosensor

Considering the worldwide health crisis associated with highly contagious severe respiratory disease of COVID-19 outbreak, the development of multiplexed, simple and rapid diagnostic platforms to detect severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) is in high demand. Here, a nucleic acid amplification-free electrochemical biosensor based on four-way junction (4-WJ) hybridization is presented for the detection of SARS-CoV-2. To form a 4-WJ structure, a Universal DNA-Hairpin (UDH) probe is hybridized with two adaptor strands and a SARS-CoV-2 RNA target. One of the adaptor strands is functionalized with a redox mediator that can be detected using an electrochemical biosensor. The biosensor could simultaneously detect 5.0 and 6.8 ag/μL of S and Orf1ab genes, respectively, within 1 h. The biosensor was evaluated with 21 clinical samples (16 positive and 5 negative). The results revealed a satisfactory agreement with qRT-PCR. In conclusion, this biosensor has the potential to be used as an on-site, real-time diagnostic test for COVID-19.

One-step fabrication of soft calcium superhydrophobic surfaces by a simple electrodeposition process

A simple, one-step electrodeposition process was rapidly performed on a metal substrate to fabricate calcium superhydrophobic surfaces in an electrolyte containing calcium chloride (CaCl₂), myristic acid (CH₃(CH₂)₁₂COOH), and ethanol, which can avoid the intricate post-processing of surface treatment. The morphology and surface chemical compositions of the fabricated superhydrophobic surfaces were systematically examined by means of SEM, XRD, and FTIR, respectively. The results indicate that the deposited surfaces were mainly composed of calcium myristate, which can dramatically lower surface free energy. The shortest process for constructing a superhydrophobic surface is about 0.5 min, and the maximum contact angle of the as-prepared surfaces can reach as high as 166°, showing excellent superhydrophobicity. By adjusting the electrodeposition time, the structure of the cathodic surface transforms from the turfgrass structure, loose flower structures, larger and dense flower structures, secondary flower structures, and then into tertiary or more flower structures. The superhydrophobic surfaces showed excellent rebound performance with a high-speed camera. After a pressing force, their hardness increases, but the superhydrophobic performance is not weakened. Inversely, the bouncing performance is enhanced. This electrodeposition process offers a promising approach for large areas of superhydrophobic surfaces on conductive metals and strongly impacts the dynamics of water droplets.

We investigated a one-step method for calcium superhydrophobic surface preparation and researched the formation process of loose, flower-like microstructures. Also, we found that the pressing force strongly impacts the dynamics of water droplets.

The dependence of Cu2O morphology on different surfactants and its application for non-enzymatic glucose detection

Herein, the Cu₂O yolk-shell nanospheres, nanocubes and microcubes were successfully prepared by a simple seed-medium process. The formation of the Cu₂O yolk-shell nanospheres can be attributed to the self-assembly process caused by the introduction of the seed medium. The formation mechanism of our obtained Cu₂O yolk-shell nanospheres and the dependence of Cu₂O morphology on different surfactants have been studied. The obtained samples were applied in the field of non-enzymatic glucose detection. The electrochemical response characteristics of the modified electrodes toward glucose were investigated by cyclic voltammetry (CV) and chronoamperometry (CA). The electrode modified with C-Cu₂O (obtained by using CTAB as surfactant) shared the highest sensitivity of 3123 μAmM^-1 cm^-2, whereas, the electrode modified with S-Cu₂O (obtained by using SDBS as surfactant) exhibited the lowest LOD of 0.87 μM and the widest linear range of 0.05-10.65 mM. All obtained sensors showed fast response to the addition of glucose. The obtained electrodes showed better responses to glucose than other coexisting interferences, indicating that the obtained electrodes had the acceptable selectivity to glucose. In addition, the stability for 5 consecutive weeks had also been studied and exhibited satisfactory results. The obtained electrode was also used to detect the glucose content in real serum. The acceptable selectivity, stability together with the excellent sensing ability in real serum make the obtained electrodes a potential for practical applications.

Dispersed Conducting Polymer Nanocomposites with Glucose Oxidase and Gold Nanoparticles for the Design of Enzymatic Glucose Biosensors

Biosensors for the determination of glucose concentration have a great significance in clinical diagnosis, and in the food and pharmaceutics industries. In this research, short-chain polyaniline (PANI) and polypyrrole (Ppy)-based nanocomposites with glucose oxidase (GOx) and 6 nm diameter AuNPs (AuNPs_{(6 nm)}) were deposited on the graphite rod (GR) electrode followed by the immobilization of GOx. Optimal conditions for the modification of GR electrodes by conducting polymer-based nanocomposites and GOx were elaborated. The electrodes were investigated by cyclic voltammetry and constant potential amperometry in the presence of the redox mediator phenazine methosulfate (PMS). The improved enzymatic biosensors based on GR/PANI-AuNPs_{(6 nm)}-GOx/GOx and GR/Ppy-AuNPs_{(6 nm)}-GOx/GOx electrodes were characterized by high sensitivity (65.4 and 55.4 μA mM⁻¹ cm⁻²), low limit of detection (0.070 and 0.071 mmol L⁻¹), wide linear range (up to 16.5 mmol L⁻¹), good repeatability (RSD 4.67 and 5.89%), and appropriate stability (half-life period (τ_1/2) was 22 and 17 days, respectively). The excellent anti-interference ability to ascorbic and uric acids and successful practical application for glucose determination in serum samples was presented for GR/PANI-AuNPs_{(6 nm)}-GOx/GOx electrode.

Developments of the Electroactive Materials for Non-Enzymatic Glucose Sensing and Their Mechanisms

A comprehensive review of the electroactive materials for non-enzymatic glucose sensing and sensing devices has been performed in this work. A general introduction for glucose sensing, a facile electrochemical technique for glucose detection, and explanations of fundamental mechanisms for the electro-oxidation of glucose via the electrochemical technique are conducted. The glucose sensing materials are classified into five major systems: (1) mono-metallic materials, (2) bi-metallic materials, (3) metallic-oxide compounds, (4) metallic-hydroxide materials, and (5) metal-metal derivatives. The performances of various systems within this decade have been compared and explained in terms of sensitivity, linear regime, the limit of detection (LOD), and detection potentials. Some promising materials and practicable methodologies for the further developments of glucose sensors have been proposed. Firstly, the atomic deposition of alloys is expected to enhance the selectivity, which is considered to be lacking in non-enzymatic glucose sensing. Secondly, by using the modification of the hydrophilicity of the metallic-oxides, a promoted current response from the electro-oxidation of glucose is expected. Lastly, by taking the advantage of the redistribution phenomenon of the oxide particles, the usage of the noble metals is foreseen to be reduced.

Electrochemical Discrimination of Salbutamol from Its Excipients in VentolinTM at Nanoporous Gold Microdisc Arrays

The emergence of specific drug–device combination products in the inhalable pharmaceutical industry demands more sophistication of device functionality in the form of an embedded sensing platform to increase patient safety and extend patent coverage. Controlling the nebuliser function at a miniaturised, integrated electrochemical sensing platform with rapid response time and supporting novel algorithms could deliver such a technology offering. Development of a nanoporous gold (NPG) electrochemical sensor capable of creating a unique fingerprint signal generated by inhalable pharmaceuticals provided the impetus for our study of the electrooxidation of salbutamol, which is the active bronchodilatory ingredient in Ventolin^TM formulations. It was demonstrated that, at NPG-modified microdisc electrode arrays, salbutamol is distinguishable from the chloride excipient present at 0.0154 M using linear sweep voltammetry and can be detected amperometrically. In contrast, bare gold microdisc electrode arrays cannot afford such discrimination, as the potential for salbutamol oxidation and chloride adsorption reactions overlap. The discriminative power of NPG originates from the nanoconfinement effect for chloride in the internal pores of NPG, which selectively enhances the electron transfer kinetics of this more sluggish reaction relative to that of the faster, diffusion-controlled salbutamol oxidation. Sensing was performed at a fully integrated three-electrode cell-on-chip using Pt as a quasi-reference electrode.

Electrosynthesis of three-dimensional nanoporous nickel on screen-printed electrode used for the determination of narirutin in citrus wastewater

In this study, an electrochemical sensor was designed for the detection of narirutin using three-dimensional nanostructured porous nickel on screen-printed electrode (3DnpNi/SPE). The modified electrode was successfully synthesized by the dynamic hydrogen bubble template method. The 3DnpNi/SPE was characterized by spectroscopic, microscopic, and electrochemical methods. The results showed that the 3DnpNi/SPE presents good electrocatalytic activity for the oxidation of narirutin. The quantification of narirutin was conducted by differential pulse voltammetry, which showed a wide concentration range (1.0 × 10^-7 - 1.0 × 10^-5 mol L^-1), with low detection limit (3.9 × 10^-8 mol L^-1), and excellent sensitivity (0.31 A L mol^-1). The proposed electrode was applied toward the determination of narirutin in yellow water sample from the citrus industry, where it presented a good degree of accuracy. The 3DnpNi/SPE showed repeatability, long-term stability, and selectivity. The results obtained showed agreement with those obtained by HPLC/DAD method. Chemical compounds studied in this article.

Orderly aligned manganese-based nanotube arrays with controllable secondary structures

By combining a hard template with a dynamic negative template, orderly aligned micrometer-length manganese nanotubes (Mn-NTs) decorated with nanopores on their walls as the secondary structure are successfully grown by electrodeposition in aqueous solution. These nanopores were characterized and analyzed statistically. It is found that these nanopores evolve along the growth direction of the Mn-NTs and their morphology is well controlled by the deposition potential. In addition, the morphology evolution of the nanopores exhibits distinguished size distribution compared with that found in conventional nanoporous foam grown solely by the dynamic template approach, which is attributed to the nanoconfinement of the hard template.

Development of an electrochemical enzyme-free glucose sensor based on self-assembled Pt-Pd bimetallic nanosuperlattices

The huge demand for the clinical diagnosis of diabetes mellitus has prompted the development of great-performance sensing platforms for glucose detection. Non-enzymatic glucose sensors are getting closer to their use in realistic applications. In this work, polyvinylpyrrolidone (PVP)-conjugated bimetallic Pt-Pd nanosuperlattices were synthesized precisely through a simple synthesis procedure, leading to controllable spherical morphologies with significantly fine and precise nanostructures in a size range of ∼3-5 nm by the reduction of Pt and Pd precursors in ethylene glycol, using an ultrasonic method. High-resolution transmission electron microscopy (HRTEM) measurements evidenced the formation of Pt-Pd bimetallic nanosuperlattices (BMNSLs). The superlattice-fringe patterns (111) of bimetallic Pt-Pd NSLs were identified in the HRTEM images, clearly showing their crystalline nature. The prepared material was used in the electrochemical oxidation of glucose using voltammetry analyses. The experimental evidence indicates that the Pt-Pd BMNSL modified glassy carbon electrode is effective for the selective amperometric detection of glucose in the presence of galactose, sucrose, fructose, lactose, and ascorbic acid. Moreover, its application in the detection of glucose in real serum and urine samples was assessed and good recoveries are achieved. The results show that a Pt-Pd bimetallic nanosuperlattice with high surface area, catalytic activity, and superior selectivity could be a promising material in the generation of novel electrodes for low-cost non-enzymatic glucose sensors.

Formation and Electrochemical Evaluation of Polyaniline and Polypyrrole Nanocomposites Based on Glucose Oxidase and Gold Nanostructures

Nanocomposites based on two conducting polymers, polyaniline (PANI) and polypyrrole (Ppy), with embedded glucose oxidase (GOx) and 6 nm size gold nanoparticles (AuNPs_(6nm)) or gold-nanoclusters formed from chloroaurate ions (AuCl₄⁻), were synthesized by enzyme-assisted polymerization. Charge (electron) transfer in systems based on PANI/AuNPs_(6nm)-GOx, PANI/AuNPs_(AuCl4⁻₎-GOx, Ppy/AuNPs_(6nm)-GOx and Ppy/AuNPs_(AuCl4⁻₎-GOx nanocomposites was investigated. Cyclic voltammetry (CV)-based investigations showed that the reported polymer nanocomposites are able to facilitate electron transfer from enzyme to the graphite rod (GR) electrode. Significantly higher anodic current and well-defined red-ox peaks were observed at a scan rate of 0.10 V s⁻¹. Logarithmic function of anodic current (log I_pa), which was determined by CV-based experiments performed with glucose, was proportional to the logarithmic function of a scan rate (log v) in the range of 0.699–2.48 mV s⁻¹, and it indicates that diffusion-controlled electrochemical processes were limiting the kinetics of the analytical signal. The most efficient nanocomposite structure for the design of the reported glucose biosensor was based on two-day formed Ppy/AuNPs_(AuCl4⁻₎-GOx nanocomposites. GR/Ppy/AuNPs_(AuCl4⁻₎-GOx was characterized by the linear dependence of the analytical signal on glucose concentration in the range from 0.1 to 0.70 mmol L⁻¹, the sensitivity of 4.31 mA mM cm⁻², the limit of detection of 0.10 mmol L⁻¹ and the half-life period of 19 days.

Optical characterization and modeling of nanoporous gold absorbers fabricated by thin-film dealloying

This work studies the optical reflectance of nanoporous gold (NPG) thin films of varying pore volume fraction (PVF) synthesized by chemical dealloying of Ag-Au alloy precursors. The fabricated samples are characterized by scanning electron microscopy, and spectral hemispherical reflectance is measured with an integrating sphere. The effective isotropic optical constants of NPG with varying PVF are modeled for the wavelength range from 0.4 to 1.6 μm using the Bruggeman effective medium theory. As the thickness of the NPG thin films is more than ten times larger than the effective penetration depth, the spectral reflectance is simply modeled with the Fresnel coefficients at the interface of air and semi-infinite NPG with different incident angles and polarizations. Consistent with the modeling results, the optical measurement data shows that the spectral normal reflectance of NPG significantly decreases with larger PVF values in the near-infrared regime. On the other hand, the reflectance increases greatly only within visible range at larger oblique angles for transverse-electric polarized waves compared to transverse-magnetic waves. Moreover, the NPG samples demonstrate good thermal stability from room temperature up to 100 °C with little changes in the temperature-dependent spectral hemispherical reflectance.

One-step formation of a hybrid material of graphene and porous Ni with highly active Ni(OH)2 used for glucose detection

A hybrid material of graphene and porous Ni with highly active Ni(OH)₂ was formed through a one-step electrochemical exfoliation assisted method. The porous Ni with a pore size of 2-10 micrometers obtained by a hydrogen bubble template method was used as the cathode while the graphite foil was used as the anode with only (NH₄)₂SO₄ as the electrolyte. Both the high surface areas of porous Ni and the oxygen radicals in graphene favored the formation of the Ni(OH)₂. It is confirmed by energy dispersion spectrum, transmission electron microscope, Raman spectroscopy, x-ray diffraction and x-ray photoelectron spectroscopy analysis. Both the active area and the glucose sensing property of the as-prepared hybrid material were estimated by electrochemical methods of cyclic voltammetry with current-voltage (C-V) curve, chronoamperometry with current-time (I-t) curve and electrochemical impedance spectroscopy analysis, respectively. It shows an extraordinary active area as well as a low charge transfer resistance and absorption resistance. As a result, a high sensitivity of 6504 μA/mM^-1 cm^-2 within a linear range of 4 μM-1.0 mM was obtained for glucose detection.

Seed-mediated Electrochemically Developed Au Nanostructures with Boosted Sensing Properties: An Implication for Non-enzymatic Glucose Detection

A new approach has been developed to improve sensing performances of electrochemically grown Au nanostructures (AuNSs) based on the pre-seeding of the electrode. The pre-seeding modification is simply carried out by vacuum thermal deposition of 5 nm thin film of Au on the substrate followed by thermal annealing at 500 °C. The electrochemical growth of AuNSs on the pre-seeded substrates leads to impressive electrochemical responses of the electrode owing to the seeding modification. The dependence of the morphology and the electrochemical properties of the AuNSs on various deposition potentials and times have been investigated. For the positive potentials, the pre-seeding leads to the growth of porous and hole-possess networks of AuNSs on the surface. For the negative potentials, AuNSs with carved stone ball shapes are produced. The superior electrode was achieved from AuNSs developed at 0.1 V for 900 s with pre-seeding modification. The sensing properties of the superior electrode toward glucose detection show a high sensitivity of 184.9 µA mM⁻¹ cm⁻², with a remarkable detection limit of 0.32 µM and a wide range of linearity. The excellent selectivity and reproducibility of the sensors propose the current approach as a large-scale production route for non-enzymatic glucose detection.

Porous Gold: A New Frontier for Enzyme-Based Electrodes

Porous gold (PG) layers modified electrodes have emerged as valuable enzyme support to realize multiple enzyme-based bioelectrochemical devices like biosensors, enzymatic fuel cells (EFCs), smart drug delivery devices triggered by enzyme catalyzed reactions, etc. PG films can be synthesized by using different methods such as dealloying, electrochemical (e.g., templated electrochemical deposition, self-templated electrochemical deposition, etc.) self-assembly and sputter deposition. This review aims to summarize the recent findings about PG synthesis and electrosynthesis, its characterization and application for enzyme-based electrodes used for biosensors and enzymatic fuel cells (EFCs) development.

Core-shell gold-nickel nanostructures as highly selective and stable nonenzymatic glucose sensor for fermentation process

Non-enzymatic electrodes based on noble metals have excellent selectivity and high sensitivity in glucose detection but no such shortcomings as easy to be affected by pH, temperature, and toxic chemicals. Herein, spherical gold-nickel nanoparticles with a core-shell construction (Au@Ni) are prepared by oleylamine reduction of their metal precursors. At an appropriate Au/Ni ratio, the core-shell Au@Ni nanoparticles as a sensor for glucose detection combine the high electrocatalytic activity, good selectivity and biological compatibility of Au with the remarkable tolerance of Ni for chlorine ions (Cl-) and poisoning intermediates in catalytic oxidation of glucose. This electrode exhibits a low operating voltage of 0.10 V vs. SCE for glucose oxidation, leading to higher selectivity compared with other Au- and Ni-based sensors. The linear range for the glucose detection is from 0.5 mmol L-1 to 10 mmol L-1 with a rapid response time of ca. 3 s, good stability, sensitivity estimated to be 23.17 μA cm-2 mM-1, and a detection limit of 0.0157 mM. The sensor displays high anti-toxicity, and is not easily poisoned by the adsorption of Cl- in solution.

The electrochemical investigation of carboxamide-PEG2-biotin-CoPc using composite MWCNTs on modified GCE: the sensitive detections for glucose and hydrogen peroxide

The electroanalytical study of a synthesized novel tetra-cobalt(ii) carboxamide-PEG₂-biotin phthalocyanine (CoTPEG₂BAPc) composite with MWCNTs to create a biosensor with a high response to glucose in the presence of H₂O₂.

Electrochemical non-enzymatic glucose sensors: recent progress and perspectives

This review summarizes recent advances in the development of electrocatalysts for non-enzymatic glucose detection. The sensing mechanism and influencing factors are discussed, and the perspectives and challenges are also addressed.

Colorimetric detection of urine glucose using a C/CdTe QDs–GOx aerogel based on a microfluidic assay sensor

A sensitive fluorescent microfluidic sensor based on carbon quantum dots (CQDs), cadmium telluride quantum dots (CdTe QDs) aerogel and glucose oxidase (GOx) for urinal glucose detection was fabricated via a simple method.

Highly monodisperse Pd-Ni nanoparticles supported on rGO as a rapid, sensitive, reusable and selective enzyme-free glucose sensor

In this work, highly monodispersed palladium-nickel (Pd-Ni) nanoparticles supported on reduced graphene oxide (rGO) were synthesized by the microwave-assisted methodology. The synthesized nanoparticles were used for modification of a glassy carbon electrode (GCE) to produce our final product as PdNi@rGO/GCE, which were utilized for non-enzymatic detecting of glucose. In the present study, electrochemical impedance spectroscopy (EIS), chronoamperometry (CA) and, cyclic voltammetry (CV) methods were implemented to investigate the sensing performance of the developed glucose electrode. The modified electrode, PdNi@rGO/GCE, exhibited very noticeable results with a linear working range of 0.05-1.1 mM. Moreover, an ultralow detection limit of 0.15 μM was achieved. According to the results of amperometric signals of the electrodes, no significant change was observed, even after 250 h of operation period. In addition, the highly monodisperse PdNi@rGO/GCE was utilized to electrochemical detection of glucose in real serum samples. In light of the results, PdNi@rGO/GCE has shown an excellent sensing performance and can be used successfully in serum samples for glucose detection and it is suitable for practical and clinical applications.

Porous Zinc Anode Design for Zn-air Chemistry

Zinc-air battery has drawn increasing attention from the whole world owing to its large energy capacity, stable working voltage, environmentally friendship, and low price. A special porous Zn with three-dimensional (3D) network frame structure, whose multistage average pore sizes can be tuned from 300 to 8 um, is synthesized in this work. It is found that there is a competition between Zn²⁺ and NH 4 + for their reduction on the supports. And the decrease of Zn²⁺ concentration and increase of NH 4 + concentration can facilitate the decrease of pore size. Potential-dynamic polarization was tested with 3-electrodes cell, aiming to characterize the electrochemical activity and corrosion properties of porous Zn and commercial Zn foil electrodes. After optimization, the porous Zn prepared with the parameters of 3 M NaBr, 1 M C₂H₃O₂NH₄, and 0.01 M C₄H₆O₄Zn shows the most negative corrosion potential of -1.45 V among all the samples, indicating the remarkable anti-corrosion property. Its discharge specific capacity is up to 812 mAh g^-1. And discharge-charge test of the porous Zn shows an initial discharge platform of 1.33 V and an initial charge platform of 1.96 V, performing a small overpotential. What's more, the porous Zn exhibits a much longer cycle life than commercial Zn foil. Our work will not only shed light on the design and synthesis of other porous metal materials, but also further promote the development of Zn-based battery electrochemistry.

Template-Assisted Electrodeposition of Porous Fe-Ni-Co Nanowires with Vigorous Hydrogen Evolution

A novel method to fabricate porous Fe-Ni-Co nanowires directly by electrodepositing into polycarbonate membranes is reported when the electrolyte pH < 0.5. Hydrogen bubbles are used as a dynamic porous template created by operating in electrolytes with very low pH to drive the proton reduction reaction. The electrolyte pH was adjusted with sulfuric acid, and the added sulfate ions are thought to help reduce bubble coalescence, but not detachment at the electrode surface, to facilitate metal deposition within the nanopores. Porous nanowires were obtained when the electrolyte pH was less than 1.0. The average alloy composition was found to be pH sensitive, which shifted from an Fe-rich porous alloy to a Ni-rich porous alloy as the electrolyte pH decreased.

Gas Bubbles in Electrochemical Gas Evolution Reactions

Electrochemical gas evolution reactions are of vital importance in numerous electrochemical processes including water splitting, chloralkaline process, and fuel cells. During gas evolution reactions, gas bubbles are vigorously and constantly forming and influencing these processes. In the past few decades, extensive studies have been performed to understand the evolution of gas bubbles, elucidate the mechanisms of how gas bubbles impact gas evolution reactions, and exploit new bubble-based strategies to improve the efficiency of gas evolution reactions. In this feature article, we summarize the classical theories as well as recent advancements in this field and provide an outlook on future research topics.