Nonenzymatic amperometric response of glucose on a nanoporous gold film electrode fabricated by a rapid and simple electrochemical method

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.

SHOX Variations in Idiopathic Short Stature in North India and a Review of Cases from Asian Countries

Objective

Short stature homeobox (SHOX) haploinsufficiency underlies idiopathic short stature (ISS) and Leri-Weill dyschondrosteosis. The worldwide prevalence of SHOX variations in ISS varies from 2.5% to 15.0%. The aim of this study was to assess the implication of SHOX variation in ISS in North Indians and compare this with other cases of SHOX variations from Asian population.

Methods

SHOX gene analysis was carried out by multiplex ligation-dependent probe amplification followed by Sanger sequencing in 54 patients with variable phenotypes. Comparison with other reports in a meta-analysis comprising the current study and 11 previous studies (n=979) was performed.

Results

SHOX analysis resulted in 12.9% positivity (7.4% deletions and 5.5% duplications). SHOX association was seen significantly related to gender, with predominance in females (p=0.047). Short arms and forearms were the only significantly associated trait seen in 51.9% of children. The overall prevalence of SHOX variation was 15.2% in Asians with ISS. No significant difference was found in geographical region-specific analysis.

Conclusion

This study summarises findings from the last decade and provides an updated picture of the prevalence of SHOX variations in Asians, emphasizing their potential as therapeutic targets in ISS patients. Further high quality, large investigations including functional validation is warranted to validate this association.

Recent Advances in Bimetallic Nanoporous Gold Electrodes for Electrochemical Sensing

Bimetallic nanocomposites and nanoparticles have received tremendous interest recently because they often exhibit better properties than single-component materials. Improved electron transfer rates and the synergistic interactions between individual metals are two of the most beneficial attributes of these materials. In this review, we focus on bimetallic nanoporous gold (NPG) because of its importance in the field of electrochemical sensing coupled with the ease with which it can be made. NPG is a particularly important scaffold because of its unique properties, including biofouling resistance and ease of modification. In this review, several different methods to synthesize NPG, along with varying modification approaches are described. These include the use of ternary alloys, immersion-reduction (chemical, electrochemical, hybrid), co-electrodeposition-annealing, and under-potential deposition coupled with surface-limited redox replacement of NPG with different metal nanoparticles (e.g., Pt, Cu, Pd, Ni, Co, Fe, etc.). The review also describes the importance of fully characterizing these bimetallic nanocomposites and critically analyzing their structure, surface morphology, surface composition, and application in electrochemical sensing of chemical and biochemical species. The authors attempt to highlight the most recent and advanced techniques for designing non-enzymatic bimetallic electrochemical nanosensors. The review opens up a window for readers to obtain detailed knowledge about the formation and structure of bimetallic electrodes and their applications in electrochemical sensing.

Porphyrin-Based Covalent Organic Frameworks with Donor-Acceptor Structure for Enhanced Peroxidase-like Activity as a Colorimetric Biosensing Platform

Hydrogen peroxide (H₂O₂) and glucose play a key role in many cellular signaling pathways. The efficient and accurate in situ detection of H₂O₂ released from living cells has attracted extensive research interests. Herein, a new porphyrin-based porous covalent organic framework (TAP-COF) was fabricated via one-step condensation of 1,6,7,12-tetrachloroperylene tetracarboxylic acid dianhydride and 5,10,15,20-tetrakis (4-aminophenyl)porphyrin iron(III). The obtained TAP-COF has high surface areas, abundant surface catalytic active sites, and highly effective electron transport due to its precisely controllable donor-acceptor arrangement and 3D porous structure. Then, the new TAP-COF exhibited excellent peroxidase-like catalytic activity, which could effectively catalyze oxidation of the substrate 3,3',5,5'-tetramethylbenzidine by H₂O₂ to produce a typical blue-colored reaction. On this basis, simple, rapid and selective colorimetric methods for in situ H₂O₂ detection were developed with the detection limit of 2.6 nM in the wide range of 0.01 to 200 μM. The colorimetric approach also could be used for in situ detection of H₂O₂ released from living MCF-7 cells. This portable sensor based on a COF nanozyme not only opens a new path for point-of-care testing, but also has potential applications in the field of cell biology and clinical diagnosis.

Applications of Nanoporous Gold in Therapy, Drug Delivery, and Diagnostics

Nanoporous gold (np-Au) has promising applications in therapeutic delivery. The promises arise from its high surface area-to-volume ratio, ease of tuning shape and size, ability to be modified by organic molecules including drugs, and biocompatibility. Furthermore, np-Au nanostructures can generate the photothermal effect. This effect can be used either for controlled release of drugs of therapeutic importance or for destroying cancer cells by heating locally. Despite the enormous potential, the research on the therapeutical use of the np-Au is still in its early stage. In this review, we discuss the current progress and future directions of np-Au for therapeutic applications.

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.

Nanoporous Gold for the Miniaturization of In Vivo Electrochemical Aptamer-Based Sensors

Electrochemical aptamer-based sensors enable real-time molecular measurements in the living body. The spatial resolution of these measurements and ability to perform measurements in targeted locations, however, is limited by the length and width of the device's working electrode. Historically, achieving good signal to noise in the complex, noisy in vivo environment has required working electrode lengths of 3-6 mm. To enable sensor miniaturization, here we have enhanced the signaling current obtained for a sensor of given macroscopic dimensions by increasing its surface area. Specifically, we produced nanoporous gold via an electrochemical alloying/dealloying technique to increase the microscopic surface area of our working electrodes by up to 100-fold. Using this approach, we have miniaturized in vivo electrochemical aptamer-based (EAB) sensors (here using sensors against the antibiotic, vancomycin) by a factor of 6 while retaining sensor signal and response times. Conveniently, the fabrication of nanoporous gold is simple, parallelizable, and compatible with both two- and three-dimensional electrode architectures, suggesting that it may be of value to a range of electrochemical biosensor applications.

A Multifunctional Electrochemical Sensor for the Simultaneous Detection of Ascorbic Acid, Dopamine, Uric Acid, and Nitrite

BACKGROUND

Ascorbic acid (AA), dopamine (DA), uric acid (UA), and nitrite (NO2-) are essential biomarkers for human metabolism and can be used to indicate some chronic diseases and metabolic disorders, including scurvy, Parkinson's disease, hyperuricemia, and kidney disease.

OBJECTIVE

A multifunctional electrochemical sensor that can integrate the detection of these species was constructed using nanoporous gold (NPG) as a recognition element to modify glassy carbon electrode (GCE).

METHODS

The electrochemical performance of the multifunctional electrochemical sensor was investigated toward AA, DA, UA, and NO2- in citrate buffer solution (CBS, 100 mM, pH 4.0) and human serum using cyclic voltammetry (CV) and differential pulse voltammetry (DPV) methods.

RESULTS

In the quaternary mixture detection, the resulting NPG/GCE electrode displayed four independent oxidation peaks with wide peak separations. Further, the NPG/GCE electrode showed good linear responses with the sensitivities of 32, 1103, 71, and 147 μA/mM/cm2 and the detection limits of 1.58, 0.17, 0.37, and 0.36 μM for AA, DA UA, and NO2-, respectively. Additionally, the NPG/GCE electrode exhibited great anti-interference and was successfully applied in human serum samples.

CONCLUSIONS

These results indicate that the NPG/GCE electrode can simultaneously and selectively detect AA, DA, UA, and NO2-, which has the potential for application and diagnosis in the screening and diagnosis of chronic diseases and metabolic disorders.

HIGHLIGHTS

A multianalyte electrochemical sensor was fabricated for human metabolites detection. The sensor displayed good performance in the simultaneous detection of AA, DA, UA, and NO2- and applied to human serum samples.

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.

Superior Degradation Performance of Nanoporous Copper Catalysts on Methyl Orange

The development of low-cost and high-efficiency catalysts for wastewater treatment is of great significance. Herein, nanoporous Cu/Cu2O catalysts were synthesized from MnCu, MnCuNi, and MnCuAl with similar ligament size through one-step dealloying. Meanwhile, the comparisons of three catalysts in performing methyl orange degradation were investigated. One of the catalysts possessed a degradation efficiency as high as 7.67 mg·g−1·min−1. With good linear fitting by the pseudo-first-order model, the reaction rate constant was evaluated. In order to better understand the degradation process, the adsorption behavior was considered, and it was divided into three stages based on the intra-particle diffusion model. Three different temperatures were applied to explore the activation energy of the degradation. As a photocatalytic agent, the nanoporous structure of Cu/Cu2O possessed a large surface area and it also had low activation energy, which were beneficial to the excellent degradation performance.

Electrochemical Oxidation of Monosaccharides at Nanoporous Gold with Controlled Atomic Surface Orientation and Non-Enzymatic Galactose Sensing

Non-enzymatic saccharide sensors are of great interest in diagnostics, but their non-selectivity limits their practical diagnostic abilities. In this study, we investigated the electrochemical oxidation of monosaccharides at nanoporous gold (NPG) catalysts with different contributions of surface crystallographic orientations. Fructose elicited no clear electrochemical response, but glucose, galactose, and mannose produced clear oxidative current. The onset potentials for oxidation of these saccharides depended on the surface atomic structure of the NPG. The oxidation potential was approximately 100 mV less positive at the Au(100)-enhanced NPG than at the Au(111)-enhanced NPG. Furthermore, the voltammetric responses significantly differed among the saccharides. Galactose was oxidized at less positive potential and exhibited a higher current response than the other saccharides. This tendency was enhanced in the presence of chloride ions. These features enabled the selective and sensitive detection of galactose at an NPG electrode without enzymes under physiological conditions. A linear range of 10 μM to 1.8 mM was obtained in the calibration plot, which was comparable to those in previously reported enzymatic galactose sensors. Thus, we demonstrated that controlling the crystallographic orientation on the nanostructured electrode surface is useful in developing electrochemical sensors.

Nanoporous Gold-Based Sensing

In recent years, the field of nanoporous metals has undergone accelerated developments as these materials possess high specific surface areas, well-defined pore sizes, functional sites, and a wide range of functional properties. Nanoporous gold (NPG) is, surely, the most attractive system in the class of nanoporous metals: it combines several desired characteristics as occurrence of surface plasmon resonances, enormous surface area, electrochemical activity, biocompatibility, in addition to feasibility in preparation. All these properties concur in the exploitatiton of NPG as an efficient and versatile sensong platform. In this regard, NPG-based sensors have shown exceptional sensitivity and selectivity to a wide range of analytes ranging from molecules to biomolecules (and until the single molecule detection) and the enormous surface/volume ratio was shown to be crucial in determining these performances. Thanks to these characteristics, NPG-based sensors are finding applications in medical, biological, and safety fields so as in medical diagnostics and monitoring processes. So, a rapidly growing literature is currently investigating the properties of NPG systems toward the detection of a multitude of classes of analytes highlighting strengths and limits. Due to the extension, complexity, and importance of this research field, in the present review we attempt, starting from the discussion of specific cases, to focus our attention on the basic properties of NPG in connection to the main sensing applications, i.e., surface enhanced Raman spectroscopy-based and electrochemical-based sensing. Owing to the nano-sized pore channels and Au ligaments, which are much smaller than the wavelength of visible light (400–700 nm), surface plasmon resonances of NPG can be effectively excited by visible light and presents unique features compared with other nanostructured metals, such as nanoparticles, nanorods, and nanowires. This characteristics leads to optical sensors exploiting NPG through unique surface plasmon resonance properties that can be monitored by UV-Vis, Raman, or fluorescence spectroscopy. On the other hand, the catalytic properties of NPG are exploited electrochemical sensors are on the electrical signal produced by a specific analyte adsorbed of the NPG surface. In this regard, the enourmous NPG surface area is crucial in determining the sensitivity enhancement. Due to the extension, complexity, and importance of the NPG-based sensing field, in the present review we attempt, starting from the discussion of specific cases, to focus our attention on the basic properties of NPG in connection to the main sensing applications, i.e., surface enhanced Raman spectroscopy-based and electrochemical-based sensing. Starting from the discussion of the basic morphological/structural characteristics of NPG as obtained during the fabrication step and post-fabrication processes, the review aims to a comprehensive schematization of the main classes of sensing applications highlighting the basic involved physico-chemical properties and mechanisms. In each discussed specific example, the main involved parameters and processes governing the sensing mechanism are elucidated. In this way, the review aims at establishing a general framework connecting the processes parameters to the characteristics (pore size, etc.) of the NPG. Some examples are discussed concerning surface plasmon enhanced Uv-Vis, Raman, fluorescence spectroscopy in order to realize efficient NPG-based optical sesnors: in this regard, the underlaying connections between NPG structural/morphological properties and the optical response and, hence, the optical-based sensing performances are described and analyzed. Some other examples are discussed concerning the exploitation of the electrochemical characteristics of NPG for ultra-high sensitivity detection of analytes: in this regard, the key parameters determing the NPG activity and selectivity selectivity toward a variety of reactants are discussed, as high surface-to-volume ratio and the low coordination of surface atoms. In addition to the use of standard NPG films and leafs as sensing platforms, also the role of hybrid NPG-based nanocomposites and of nanoporous Au nanostructures is discussed due to the additional increase of the electrocatalytic acticvity and of exposed surface area resulting in the possible further sensitivity increase.

Roles of TiO2 in the highly robust Au nanoparticles-TiO2 modified polyaniline electrode towards non-enzymatic sensing of glucose

Along with the rise of diabetes mellitus issue, glucose sensor has become an imperative tool for healthcare. Studies have been widely conducted on electrode materials for glucose sensors; metal nanoparticles and/or oxide particles in its nano-size are reported to exhibit remarkable electrocatalytic activities in the non-enzymatic glucose sensors. However, the decoration processes of metal nanoparticles or nano-sized oxides are known to be tedious and time-consuming. In addition, the processes usually result in great amount of waste solution emission. In this study, therefore, an Au nanoparticles (NPs)-TiO₂ modified polyaniline (PANI) composite is practiced towards the applications of non-enzymatic glucose sensors, by using a facile and time-saving thermal reduction and by electrodeposition techniques with low waste solution emission. Au NPs, which is modified with TiO₂ nanoparticles in its optimized amount, performs the highest electrocatalytic activity to the oxidation of glucose in alkaline solution. The stability of Au NPs-TiO₂/PANI is superior to those of most reported results over 70 days. The sensitivity and detection limit are 379.8 μA mM^-1 cm^-2 and 0.15 μM, respectively. High selectivity of Au NPs-TiO₂/PANI is also confirmed by the interference test. Spill-over effect of OH^- between Au NPs and TiO₂, which is the main reason for the improved catalytic activity, is described in this study.

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.

Alleviating concentration polarization: a micro three-electrode interdigitated glucose sensor based on nanoporous gold from a mild process

Precisely detecting the concentration of glucose in the human body is an attractive way to prevent or diagnose diabetes. Compared with the traditional enzyme-based electrochemical glucose sensors, the non-enzymatic ones have gradually come to people's attention recently. By integrating three electrodes into one device, glucose sensors can achieve superior performance and are convenient to carry. Herein, a non-enzymatic three-electrode interdigitated glucose sensor (TEIDGS) based on nanoporous gold is designed and fabricated. To our best knowledge, it is the first time that interdigitated electrodes are combined in a single non-enzymatic glucose sensor device. Due to the advantage of the interdigitated structure and the smart design of the three-electrode circuit board, the TEIDGS can effectively reduce concentration polarization and achieve a high detective sensitivity for glucose of 1217 μA mM-1 cm-2 and 343 μA mM-1 cm-2 in the ranges of 0.001-0.590 mM and 0.59-7.00 mM, respectively. Moreover, a low detection limit of 390 nM can be reached. In addition, this TEIDGS possesses excellent selectivity for glucose among other interferents. Strikingly, after three weeks of operation, it can still retain a high detection performance. This work will certainly provide an efficient structure and proper catalytic material choice for future non-enzymatic glucose sensors.

Ultrafast one-pot anodic preparation of Co3O4/nanoporous gold composite electrode as an efficient nonenzymatic amperometric sensor for glucose and hydrogen peroxide

For fabrication of composite electrode, one-pot strategy is highly attractive for convenience and efficiency. Here, a self-supporting Co₃O₄/nanoporous gold (NPG) composite electrode was one-pot prepared via one-step in situ anodization of a smooth gold electrode in a CoCl₂ solution within 100 s. It worked as a bifunctional electrocatalyst for glucose oxidation and H₂O₂ reduction in NaOH solution. Under optimized conditions, the electrocatalytic oxidation of glucose exhibits a wide linear range from 2 μM to 2.11 mM with a limit of detection as low as 0.085 μM (S/N = 3) and an ultrahigh sensitivity of 4470.4 μA mM^-1 cm^-2. Detection of glucose in human serum samples are also realized with results comparable to those from local hospital. The electrocatalytic reduction of H₂O₂ shows a linear response range from 20 μM to 19.1 mM and a high sensitivity of 1338.7 μA mM^-1 cm^-2. The present results demonstrate that the facilely prepared Co₃O₄/NPG is a promising nonenzymatic sensor for rapid amperometric detection of glucose and H₂O₂ with ultrasensitivity, high selectivity, satisfactory reproducibility, good stability and long duration.

Hierarchical bi-continuous Pt decorated nanoporous Au-Sn alloy on carbon fiber paper for ascorbic acid, dopamine and uric acid simultaneous sensing

In this work, Pt nanoparticles modified nanoporous AuSn(Pt@NP-AuSn) alloy on Ni buffered flexible carbon fiber paper (CFP) is fabricated by a simple replacement reaction in which NP-AuSn is fabricated by controllable dealloy of electrodeposited Au-Sn alloy films. The as prepared Pt@NP-AuSn/Ni/CFP possesses hierarchical pore structure, high specific surface area and excellent catalytic activity. Due to the bi-functions of both the large surface area of nanoporous metal and macroporous of carbon fiber paper facilitating mass transfer, the Pt@NP-AuSn/Ni/CFP shows high sensitivity of detecting ascorbic acid (AA), dopamine (DA) and uric acid (UA), with sensitivities of 0.14 μA μM^-1 cm^-2, 15.23 μA μM^-1 cm^-2, 0.28 μA μM^-1 cm^-2 under the concentration ranging from 200 to 2000 μM, 1-10 μM, and 25-800 μM for AA, DA and UA, respectively. Further, the Pt@NP-AuSn/Ni/CFP possesses long-term stability of sensing AA, DA and UA and presents great anti-interference towards a variety of common compounds in body fluid. All of these results manifest the Pt@NP-AuSn/Ni/CFP can be a promising candidate for the application of the electrochemical sensor for simultaneous detection of AA, DA and UA.

Ultra-rapid fabrication of highly surface-roughened nanoporous gold film from AuSn alloy with improved performance for nonenzymatic glucose sensing

Using one-step anodization strategy, a nanoporous gold film (HNPG) with large surface area was rapidly fabricated on Au₈₀Sn₂₀ (wt%) alloy in just 80 s. The formation of highly surface-roughened nanoporous structures results from a complex process of electrochemical dealloying of Sn component from AuSn alloy, anodic electrodissolution, disproportion and deposition of Au component, and spontaneous redox reaction between electrodissolved Sn²⁺ and AuCl₄^－species at the applied anodic potential. As-prepared HNPG/AuSn shows enhanced electrochemical performance for glucose oxidation in alkaline electrolyte. At a low potential of 0.1 V (vs. SCE), it offers a short response time of 4 s, a wide linear detection range of 2 μM to 8.11 mM, an ultralow detection limit of 0.36 μM (S/N = 3), an ultrahigh sensitivity of 4374.6 μA cm^-2 mM^-1, and satisfactory selectivity and reproducibility. Specifically, after 6 weeks, no obvious loss of glucose amperometric signal was observed on HNPG/AuSn. The facile preparation and excellent sensing performance of HNPG/AuSn electrode make sure that it is a promising candidate for advanced enzyme-free glucose sensors.

Recent advances in electrochemical non-enzymatic glucose sensors - A review

This review encompasses the mechanisms of electrochemical glucose detection and recent advances in non-enzymatic glucose sensors based on a variety of materials ranging from platinum, gold, metal alloys/adatom, non-precious transition metal/metal oxides to glucose-specific organic materials. It shows that the discovery of new materials based on unique nanostructures have not only provided the detailed insight into non-enzymatic glucose oxidation, but also demonstrated the possibility of direct detection in whole blood or interstitial fluids. We critically evaluate various aspects of non-enzymatic electrochemical glucose sensors in terms of significance as well as performance. Beyond laboratory tests, the prospect of commercialization of non-enzymatic glucose sensors is discussed.

Preparation, Modification, Characterization, and Biosensing Application of Nanoporous Gold Using Electrochemical Techniques

Nanoporous gold (np-Au), because of its high surface area-to-volume ratio, excellent conductivity, chemical inertness, physical stability, biocompatibility, easily tunable pores, and plasmonic properties, has attracted much interested in the field of nanotechnology. It has promising applications in the fields of catalysis, bio/chemical sensing, drug delivery, biomolecules separation and purification, fuel cell development, surface-chemistry-driven actuation, and supercapacitor design. Many chemical and electrochemical procedures are known for the preparation of np-Au. Recently, researchers are focusing on easier and controlled ways to tune the pores and ligaments size of np-Au for its use in different applications. Electrochemical methods have good control over fine-tuning pore and ligament sizes. The np-Au electrodes that are prepared using electrochemical techniques are robust and are easier to handle for their use in electrochemical biosensing. Here, we review different electrochemical strategies for the preparation, post-modification, and characterization of np-Au along with the synergistic use of both electrochemistry and np-Au for applications in biosensing.

Electrochemical nonenzymatic sensing of glucose using advanced nanomaterials

An overview (with 376 refs.) is given here on the current state of methods for electrochemical sensing of glucose based on the use of advanced nanomaterials. An introduction into the field covers aspects of enzyme based sensing versus nonenzymatic sensing using nanomaterials. The next chapter cover the most commonly used nanomaterials for use in such sensors, with sections on uses of noble metals, transition metals, metal oxides, metal hydroxides, and metal sulfides, on bimetallic nanoparticles and alloys, and on other composites. A further section treats electrodes based on the use of carbon nanomaterials (with subsections on carbon nanotubes, on graphene, graphene oxide and carbon dots, and on other carbonaceous nanomaterials. The mechanisms for electro-catalysis are also discussed, and several Tables are given where the performance of sensors is being compared. Finally, the review addresses merits and limitations (such as the frequent need for working in strongly etching alkaline solutions and the need for diluting samples because sensors often have analytical ranges that are far below the glucose levels found in blood). We also address market/technology gaps in comparison to commercially available enzymatic sensors. Graphical Abstract Schematic representation of electrochemical nonenzymatic glucose sensing on the nanomaterials modified electrodes. At an applied potential, the nanomaterial-modified electrodes exhibit excellent electrocatalytic activity for direct oxidation of glucose oxidation.

Nickel-gold bimetallic monolayer colloidal crystals fabricated via galvanic replacement as a highly sensitive electrochemical sensor

Bimetallic Ni-Au monolayer colloidal crystals (MCCs) were fabricated by galvanic replacement of Ni monolayers with Au salt. The influence of Au concentration used in the galvanic replacement solutions on the morphology and structure of the resulting Ni-Au surface is studied. It was found that the use of monolayer colloidal crystals, which display cohesive structure formations across the monolayer, results in the galvanic replacement reaction occurring more evenly over the surface when compared to the thin film counterpart. The fabricated devices were analyzed under alkaline conditions using chronoamperometric techniques to detect glucose concentrations ranging between 20 μM and 10 mM. The optimum Ni-Au MCC substrate was produced using 0.1 mM Au salt solution and showed a very low experimental detection limit of 14.9 μM and a calculated sensitivity of 506 μA mM^-1 cm^-2, which was ∼3 times larger than that of the plain Ni MCC substrate. The Ni-Au MCC substrate also showed minimal current response changes in the presence of common physiological contaminants, thus being a highly selective electrochemical glucose sensor.