Nanoporous Gold Films Research Articles

Performance simulation of terahertz waveguide resonance biochemical sensor based on nanoporous gold films

A highly sensitive terahertz (THz) waveguide resonance biochemical sensor is designed and simulated. The sensor consists of a silicon prism, a dielectric layer and a nanoporous gold film. The nanoporous gold film acts as both a THz waveguiding layer and a biochemical molecular enrichment layer, which can enhance the interaction between the THz waveguide mode and the adsorbed biochemical molecules, consequently improving the sensor’s sensitivity. When the THz transverse electric (TE) or transverse magnetic (TM) modes are excited by the prism-coupling method, the THz absorption of the nanoporous gold film results in the sharp resonance dips in the THz reflection spectrum. The resonance frequencies of the THz waveguide modes and the sensitivity to either liquid refractive index (RI) or adsorbed molecules can be determined with the measured reflection spectra, and the sensor’s sensitivity and its figure of merit (FOM) can be improved by adjusting the thickness and RI of the dielectric layer. The simulation results at 45º incidence angle indicate that the resonance frequencies of the TE and TM modes of the sensor linearly change with increasing either liquid RI or the amount of adsorbed molecules, and the RI sensitivity and the FOM with the TM mode are 13.42 THz/RIU and 167.70/RIU, respectively. Compared with the TM mode, the TE mode has a lower sensitivity to lqiuid RI but a high sensitivity to adsorbed molecules. The reason for these differences is that with the TE mode the evanescent field penentrating out of the nanopous gold film is weaker than that with the TM mode.

Highly sensitive and selective nanostructured microbiosensors for glucose and lactate simultaneous measurements in blood serum and in vivo in brain tissue

Highly sensitive and selective nanostructured lactate and glucose microbiosensors for their in vivo simultaneous determination in rat brain were developed based on carbon fiber microelectrodes (CFM) modified with nanoporous gold (NPG) using the Dynamic Hydrogen Bubble Template (DHBT) method. Electrodeposition of platinum nanoparticles (PtNP) onto the NPG film enhances the sensitivity and the electrocatalytic properties towards H2O2 detection. The nanostructured microelectrode platform was modified by glucose oxidase (GOx) and lactate oxidase (LOx) enzyme immobilization. High selective measurements were achieved by covering with a perm-selective layer of electropolymerized m-phenylenediamine, deposition of a Nafion® film and by using a null sensor. The morphological characteristics and electroanalytical performance of the microbiosensors were assessed, by scanning electron microscopy and electrochemical techniques, respectively.The PtNP/NPG/CFM shows a high sensitivity to H2O2 (5.96 A M-1 cm-2) at 0.36 V vs. Ag/AgCl, with a linear range from 0.2 to 200 μM, and an LOD of 10 nM. The microbiosensors were applied to the simultaneous determination of lactate and glucose in blood serum samples. Moreover, the basal extracellular concentrations of lactate and glucose were measured in vivo in four different rat brain structures. These results support the potential of the microbiosensor to be used as a valuable tool to investigate brain neurochemicals in vivo.

Coralloid-Pt nanodendrites decorated nanoporous gold films with exceptional ORR performance and ab initio DFT studies

Deposition of trace amounts of Pt onto nanoporous gold ligaments (NPG-Pt) has demonstrated promising performance of low-Pt electrocatalysts for oxygen reduction reaction (ORR); however, improving the activity of ORR remains challenging because of the difficulty in understanding the electronic effect between Pt and NPG as well as the absence of ORR mechanism studies on NPG-Pt. Here we show that NPG-Ptx (x = 1 ∼ 4), unique coralloid-Pt nanodendrites decorated nanoporous gold films through underpotential deposition/in-situ reduction replacement (UPD/IRR) strategy, exhibit significantly enhanced ORR activities. Among them, NPG-Pt3 exhibits the best ORR activity compared with the others and Pt/C in acidic media. Density functional theory (DFT) studies demonstrate the ORR mechanism and rate-determining step of NPG-Ptx follow the free energy diagrams. Furthermore, the projected density of state (PDOS) results reveal a relatively weaker O2 reaction capacity on the top side of Pt (Pttop) than the side site (Ptside) for NPG-Ptx. The increase of d-band center for NPG-Ptx pushes up the energy of the antibonding state above the Fermi level, and then the backflow of electrons into the system makes the energy more stable, optimizing the ORR activity. These results provide new inspirations for the development of low-Pt electrocatalysts for energy technologies in a rational manner.

Effect of Nanoscale Confinement on Polymer-Infiltrated Scaffold Metal Composites

Most research on polymer composites has focused on adding discrete inorganic nanofillers to a polymer matrix to impart properties not found in polymers alone. However, properties such as ion conductivity and mechanical reinforcement would be greatly improved if the composite exhibited an interconnected network of inorganic and polymer phases. Here, we fabricate bicontinuous polymer-infiltrated scaffold metal (PrISM) composites by infiltrating polymer into nanoporous gold (NPG) films. Polystyrene (PS) and poly(2-vinylpyridine) (P2VP) films are infiltrated into the ∼43 nm diameter NPG pores via capillary forces during thermal annealing above the polymer glass transition temperature (Tg). The infiltration process is characterized in situ using spectroscopic ellipsometry. PS and P2VP, which have different affinities for the metal scaffold, exhibit slower segmental dynamics compared to their bulk counterparts when confined within the nanopores, as measured through Tg. The more attractive P2VP shows a 20 °C increase in Tg relative to its bulk, while PS only shows a 6 °C increase at a comparable molecular weight. The infiltrated polymer, in turn, stabilizes the gold nanopores against temporal coarsening. The broad tunability of these polymer/metal hybrids represents a unique template for designing functional network composite structures with applications ranging from flexible electronics to fuel cell membranes.

Gold Nanoparticles/Carbon Nanotubes and Gold Nanoporous as Novel Electrochemical Platforms for L-Ascorbic Acid Detection: Comparative Performance and Application

Herein, the effects of nanostructured modifications of a gold electrode surface in the development of electrochemical sensors for L-ascorbic acid detection have been investigated. In particular, a bare gold electrode has been modified by electrodeposition of gold single-walled carbon nanotubes (Au/SWCNTs) and by the formation of a highly nanoporous gold (h-nPG) film. The procedure has been realized by sweeping the potential between +0.8 V and 0 V vs. Ag/AgCl for 25 scans in a suspension containing 5 mg/mL of SWCNTs in 10 mM HAuCl4 and 2.5 M NH4Cl solution for Au/SWCNTs modified gold electrode. A similar procedure was applied for a h-nPG electrode in a 10 mM HAuCl4 solution containing 2.5 M NH4Cl, followed by applying a fixed potential of −4 V vs. Ag/AgCl for 60 s. Cyclic voltammetry and electrochemical impedance spectroscopy were used to characterize the properties of the modified electrodes. The developed sensors showed strong electrocatalytic activity towards ascorbic acid oxidation with enhanced sensitivities of 1.7 × 10−2 μA μM−1cm−2 and 2.5 × 10−2 μA μM−1cm−2 for Au/SWCNTs and h-nPG modified electrode, respectively, compared to bare gold electrode (1.0 × 10−2 μA μM−1cm−2). The detection limits were estimated to be 3.1 and 1.8 μM, respectively. The h-nPG electrode was successfully used to determine ascorbic acid in human urine with no significant interference and with satisfactory recovery levels.

Fast attenuation of high-frequency acoustic waves in bicontinuous nanoporous gold

We studied the formation and attenuation of GHz elastic waves in free-standing nanoporous gold films by MeV ultrafast electron diffraction and finite element simulations. By tracing the evolution of the high frequency acoustic waves in time domain, we found that the bicontinuous nanoporous structure in nanoporous gold films results in three-dimensionally acoustic response with low coherence, leading to fast attenuation of the elastic waves in comparison with solid gold films. The morphologically dominated dynamics indicates the nanoporosity plays an important role in the high-frequency acoustic energy relaxation, which shines a light on the applications of dealloyed nanoporous materials in nanodevices and sensors as GHz and THz acoustic filters and dampers.

Formation of Nanoporous Gold Film on Ti by Anodization in Oxalic Acid

Abstract A nanoporous gold (NPG) film was formed on a Ti sheet or sputter-deposited thin Ti film by the anodization of a thin gold film on the Ti substrates in oxalic acid. A remarkably low anodic current of the Ti sheet compared with that of the Al sheet indicates that Ti is a stable substrate for the NPG film formed by the anodization. It is also confirmed that the preanodization of the Ti sheet significantly improves the adhesion of the NPG film to Ti. By increasing the anodic potential, NPG film was formed on sputter-deposited thin Ti film with a thickness of 130 nm.

Mass Transport in Nanoporous Gold and Correlation with Surface Pores for EC1 Mechanism: Case of Ascorbic Acid

AbstractThe present work correlates the mass transport of ascorbic acid (AA), which undergoes an electrochemical reaction accompanied by a first‐order chemical reaction (EC1 mechanism), with the size of surface pores of nanoporous gold (NPG) films. NPG films were electrodeposited on gold microelectrodes, generating polycrystalline, and highly porous surfaces. Studies of AA electrooxidation reveal mainly diffusional mass transport driven by EC1 pathways on the NPG electrodes prepared by changing the deposition potential. Similar studies on the NPGs prepared by changing the deposition time exhibit mainly diffusional transport at shorter deposition times, and largely an adsorption process driven by EC1 at longer deposition times. Such transition in the reaction pathways from diffusion EC1 to adsorption EC1 is correlated with the evolution of micrometer large surface pores in NPG films prepared at longer deposition times, allowing the diffusion of AA from the bulk solution to the volume of NPG, which enhances the adsorption probability.

A facile approach for fabrication of three-dimensional platinum-nanoporous gold film and its application for sensitive detection of microRNA-126 combining with catalytic hairpin assembly reaction

MicroRNAs (miRNAs) as important biomarkers are closely related to cancers. Herein, a easy-facilitative nanocomposite which consists of Pt nanoparticles (PtNPs) and nanoporous gold (NPG) structure has been successfully prepared on Au electrode through a facile two-step square wave voltammetry (SWV) combining with electrodeposition method. Scanning electron microscopy (SEM), energy-dispersive spectroscopy (EDS), and cyclic voltammetry (CV) were used for microscopic analysis and electrochemical studies of the PtNPs/NPG modified electrode. Combined with the well-designed catalytic hairpin assembly (CHA) amplification strategy, the small amount of Pt particles presented over the NPG film electrode substantially improved the electrocatalytic activity in the determination of microRNA-126 (miRNA-126), and a significant increase of amperometric current response accompanied with low background signal could be monitored at PtNPs/NPG electrode compared to those of bare Au and NPG electrodes. Under optimal conditions, a wide linear range of 0.5–500 pM for the amperometric assay of miRNA-126 was achieved along with a limit of detection (S/N = 3) of 0.17 pM. We further applied this assay to detect target miRNA in the total RNA extract of H1975 cells. Therefore, the proposed biosensing platform exhibits good analytical performance such as facile, ultrasensitive, low-cost, and high anti-interference capability, which promises to be a potential and beneficial tool for biomedical research and early clinical diagnosis of cancers through detection of multiple miRNA biomarkers.

High uniaxial buckling strain for measuring the mechanical properties of nanoporous gold films

Excellent studies have been conducted to understand the mechanical behavior of thin films by buckling the films using heat-shrinkable substrates. A buckling-based method [Stafford et al., Nat. Mater. 3 (2004) 545] has been adopted to measure the mechanical properties of nanoporous gold (NPG) films. This method is highly suitable under low-strain conditions; however, we attempted to use this approach under high-strain conditions. The calculated (8.2 GPa) and measured (10 ± 1.3 GPa) values of Young's modulus are remarkably near the literature value (8.8 GPa). Owing to the high-strain conditions, the effects of pore size on the Young's modulus [J. Erlebacher, J. Mathur, Appl. Phys. Lett. 90 (2007) 061910] may not be considered, and the cracks and delamination of the NPG films from the shrunken substrate were considered to interpret the mechanical behavior of the films.

A rechargeable all-solid-state sodium peroxide (Na2O2) battery with low overpotential

Na–O2 batteries have been attracting attention owing to their intrinsically high theoretical energy density. Several Na–O2 systems can produce various discharge products with different electrochemical performances. For example, sodium superoxide (NaO2) batteries have a low overpotential, and sodium peroxide (Na2O2) batteries have a high capacity. Studies of Na2O2 batteries are relatively scarce, owing to the difficulty of forming pure Na2O2 discharge products. A pure Na2O2 battery system is highly desirable for fully exploring the formation and decomposition of Na2O2 in Na–O2 batteries and evaluating their potential. This model of a Na2O2 battery should also be compatible with in situ characterization. To this end, we constructed a simple rechargeable all-solid-state Na2O2 battery. Using a nanoporous gold film as the cathode and Na–β″-Al2O3 as a solid electrolyte, we assembled a Na–O2 battery that can produce and decompose Na2O2. The all-solid-state Na–O2 battery is a simple model for conducting in situ ambient-pressure x-ray photoelectron spectroscopy (APXPS) investigations. The battery can be cycled at a low overpotential (≈450 mV). Qualitative and quantitative analyses of the APXPS and Raman results demonstrated that Na2O2 was the main discharge product and its transformation occurred during the charge and discharge periods. The operando investigation of this type of all-solid-state Na2O2 battery can help in the comprehensive exploration of the potential of Na–O2 batteries.

Facile fabrication of nanoporous gold films for surface plasmon resonance (SPR) sensing and SPR-based SERS

NPG films with controllable thickness and smaller pores are prepared by the sputtering-low-temperature dealloying process, and the spatial overlap of the SPP and the adsorbed analyte molecules offers the NPG film significant SERS enhancement.

High sensitive titanium/chitosan-coated nanoporous gold film electrode for electrochemical determination of acetaminophen in the presence of piroxicam

In this paper, the electro-catalytic activity of nano-porous gold film (NPGF) electrode modified with titanium (Ti) and chitosan (CS) is studied with regard to the determination of acetaminophen (AC) and piroxicam (PX). Underpotential deposition (UPD) is employed to cover Ti on NPGF electrode surface (TiNPGF), and then electrochemical method is used to modify the TiNPGF electrode surface using CS film (CS-TiNPGF). Scanning electron microscopy (SEM) and energy-dispersive X-ray spectroscopy (EDX) are employed for the characterization of the attained CS-TiNPGF electrode. CS-TiNPGF electrode shows great efficiency to the electrochemical oxidation of AC with a low detection limit 0.01 μM. The result acquired from differential pulse voltammetry (DPV) technique is linearly dependent on AC concentration in the ranges of 0.06–50.0 μM with a correlation coefficient of 0.9890, and in the range of 60.0–700.0 μM with a correlation coefficient of 0.9940. CS-TiNPGF electrode also shows excellent performance for determination of AC in the presence of P X . This electrode is used to find out the content of acetaminophen and piroxicam in biological and pharmaceutical samples using the standard addition method.

Rapid Microfluidic Electrochemical Sensor for the Detection of Heavy Metal Ions in Water Sample

Heavy metals are naturally found in the earth’s crust. A relatively dense metal or metalloid which is known for its potential toxicity in an environmental context is termed as Toxic Heavy Metal. They include cadmium, mercury, lead, arsenic, copper, silver etc. to name a few. Human activities like mining, production of industrial wastes, vehicle emissions, manufacturing paints, disposal of microplastics in water bodies are few examples of how these metals are exposed to open vicinities that lead to their direct interaction with living beings. Plants uptake heavy-metal polluted water is then consumed by animals. Ingestion of these plants and animal further becomes the largest source of heavy metal concentration in humans. They are hard to metabolize that causes them to bioaccumulate in the system of the living being. These metals bind to vital cellular components, such as structural proteins, enzymes, and nucleic acids, and interfere with their proper functioning. The symptoms and effects vary as per the concentration of the metal or metal compound. In most cases, carcinogenic effects have been observed in central and peripheral nervous system, and circulatory system of the organism. Therefore, there is a need to develop a fast, convenient, accurate, and cost-effective microfluidic sensor platform for heavy metal ions in water bodies of both urban and rural scenarios.In this project, a microfluidic device design (as shown in the Figure 1) is developed adapting a logical sequence of microchannels and microstructures representing the mixing, detection, and separation zones with consideration of desired operation. This is followed by incorporation of an optical and electrochemical sensing system for increased precision of heavy metal ion detection. The electrochemical system includes three electrodes such as working electrode, counter electrode and reference electrode. The potential at working electrode start with -0.4 V and switching potential at 1.2 V while the counter electrode at 0 V and standard reference electrode at 0.23 V. The three-electrode cell configuration consists of a nanoporous gold film (NPGF) as working electrode, Pt wire as the counter electrode and Ag/AgCl as the reference electrode. The electrode behavior is investigated using cyclic voltammetric studies in the presence of the electrolyte 10mM K3Fe(CN)6 in 0.1M KCl. The inlet velocity achieved through hydrodynamic focusing facilitates the rapid detection of heavy metal ions in the electroanalysis unit.In this study, a simulation model has been created using COMSOL Multiphysics® Modelling Software using both laminar flow physics for Fluid Transport and Electroanalysis modules to obtain Cyclic Voltammetry results for heavy metal ion detection within the microfluidic platform. The transport properties of water are used for simulation studies. Diffusion coefficient for the two species K3Fe(CN)6 and KCl (K3Fe(CN)6)= 7.6x10-10 m2/s ; (KCl) = 2.47x10-9 m2/s. Starting concentrations of the two species, C1 (K3Fe(CN)6) = 10 mM = 10 mol/m3and C2 (KCl) = 0.1M = 100 mol/m3. The scan rate applied is 0.1V/s. Figure 2 represents the results for the simulation model. These simulation results are in good agreement with the experimental results of the same. Further investigation on the microfluidic sensor for selective detection of heavy metal ions in water samples is in progress. Figure 1

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.

An Electrochemical Platform for Determination of Isoprenaline in the Presence of Acetaminophen Based on a Nanoporous Gold Film Electrode Modified With Polyaniline

In this paper, the fabrication of polyaniline (PANI) coating onto nano-porous gold film (PANI-NPGF) electrode is reported using an easy method. The covering electrode with PANI is carried out on the surface of NPGF electrode by cyclic voltammetry (CV). The electrochemical behavior of isoprenaline (IP) on PANI-NPGF electrode is investigated by cyclic and differential pulse voltammetry (DPV) techniques, and the capability of the PANI-NPGF electrode for simultaneous determination of IP and acetaminophen (AC) is checked. PANI-NPGF shows an outstanding performance towards oxidation of IP with high sensitivity and, therefore, a low limit of detection ( $7\times 10^{-10}$ mol/L) for IP. The obtained results show that the differential pulse response of IP is linear at two consecutive concentration ranges of $2.5\times 10^{-9}$ to $1.0\times 10^{-5}$ mol/L and $1.0\times 10^{-5}$ to $3.0\times 10^{-4}$ mol/L with linear coefficients of 0.9941 and 0.9930, respectively. Moreover, the proposed electrode remarkably shows good repeatability, rapid response, stability, and selectivity. The suggested sensor is also used for determination of IP in pharmaceutical samples.

Nanoporous gold film: Surfactant-assisted synthesis, anodic oxidation and sensing application in electrochemical determination of quercetin

In this research for a first time, the effect of cationic, anionic and nonionic surfactants on the gold nanostructures is studied using electrochemical techniques. The results present the size of gold nanostructures depends to the concentration surfactants. Improvement of the designing method is recommended for the anionic surfactant. On the other hand, nonionic and cationic surfactants show less importance for the present study. Also, the optimal concentration of the different surfactants is investigated in fabrication of the nanoporous gold film (NPGF). The studies are accomplished by cyclic voltammetry (CV), Brunauer-Emmett-Teller and scanning electron microscopy techniques. Further, the electrocatalytic behaviour of the gold nanostructures is investigated using quercetin (QU) as an analyte. The peak current of QU at the surface of NPGF shows two linear dynamic ranges from 0.01 to 12.0 and 12.0–100.0 μM. Using the data, detection limit is obtained 1.1 nM for QU. The voltammetric sensing studies suggest that the NPGF will become a potential material in the field of electrochemical sensors.

Light welding Au nanoparticles assembled at water-air interface for monolayered nanoporous gold films with tunable electrocatalytic activity

Nanoporous gold film (NPGF) has shown great potential for photonics, catalysis, sensing, and renewable energy. Herein, we report a monolayered NPGF with tunable electrocatalytic activity for improved methanol electrooxidation and H2O2 detection. The NPGFs were fabricated via interfacial self-assembly of Au nanoparticles (NPs) with different sizes and a subsequent light welding process. Amongst the NPGFs made from 16, 30, 55, and 70 nm Au NPs (denoted as x nm-NPGF, where x represents the size for the Au NPs), the 16 nm-NPGF shows the highest electrocatalytic activity, which is attributed to the synergistic contribution from its largest surface area, high conductivity, and the smallest hyperboloid-like ligaments that expose more high-index facets. Consequently, the optimized 16 nm-NPGF delivers a large current density of 151 μA cm−2 (at 0.22 V vs. saturated calomel electrode in 0.1 M KOH and 1.0 M methanol) for methanol electrooxidation. Moreover, it as well shows a good linear range (from 0.005 to 45 mM) for H2O2 detection, reaching a detection limit of 2.56 μM and sensitivity of 156.6 μA mM−1 cm−2. Our studies, thus, offer a low-temperature, solution-processable approach to fabricate monolayered NPGF from easily available Au NPs, without harsh dealloying process.

New strategy to fabricate a polydopamine functionalized self-supported nanoporous gold film electrode for electrochemical sensing applications

In this work, a polydopamine functionalized self-supported nanoporous gold film (PDA@NPGF) was prepared over a Au surface via anodization followed by chemical reduction method using dopamine as a reducing agent for the first time. Field emission scanning electron microscopy (FE-SEM) and energy dispersive X-ray analysis (EDX) were used to characterize the surface morphology and for elemental analysis. The electrocatalytic activity and sensing ability of the PDA@NPGF platform were examined towards hydrogen peroxide (H2O2) and dopamine (DA) detection using cyclic voltammetry and amperometry techniques. Cyclic voltammetry results confirm the excellent catalytic activity of the PDA@NPGF electrode for H2O2 and DA sensing compared to that of bare Au, and nanoporous gold film (NPGF) electrodes. The electrochemical determination of H2O2 and DA at PDA@NPGF was evaluated by amperometry by applying a constant potential of −0.13 V and 0.20 V (vs. Ag/AgCl) in the linear range of 1–100 µM, respectively. The detection limit of the developed sensor for H2O2 and DA analysis was calculated using the corresponding calibration plots and the values were found to be 0.1 µM and 0.27 µM (S/N = 3), respectively.

Amperometric microsensor based on nanoporous gold for ascorbic acid detection in highly acidic biological extracts

Tuning the electrocatalytic properties of high surface area porous metallic frameworks like Nanoporous Gold (NPG) by tailoring the structure is a convenient strategy to design electrochemical sensors. Accordingly, an NPG-based sensitive, selective and robust electroanalytical platform was designed for the detection of ascorbic acid (AA) in acidic extracts of Aspergillus fumigatus fungus and Arabidopsis thaliana leaves. NPG films were electrodeposited on a gold microelectrode by potentiostatic electrodeposition and characterized by electron microscopy techniques, which confirmed the morphology and highly porous structure resembling nanowires-type pure gold fractals. The electrodeposition parameters, particularly deposition potential and time, were optimized to achieve large and selective amperometric detection of AA on the NPG modified electrodes. Faster electron transfer kinetics was manifested on the 0.3 V shift in overpotential and remarkable enhancement of the oxidation peak current as compared with bare gold electrode. Amperometric measurements were performed at 0.3 V vs. Ag/AgCl(sat. KCl) in the highly acidic electrolyte solution employed to extract ascorbate from biological samples and minimize its autoxidation. The sensitivity of conventional Au-microelectrodes was increased about one thousand-fold upon modification with NPG film, reaching 2 nA μmol−1 L−1. The detection limit for AA based on a linear current-concentration calibration plot was found to be 2 μmol L−1. The NPG-based microsensor was demonstrated to be selective, reproducible and stable, and was employed for determinations of AA concentration in highly acidic biological extracts.