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Fermi-level pinning caused by the kinetic damage during metallization has been recognized as one of the major reasons for the non-ideal behavior of electrical contacts, forbidding reaching the Schottky–Mott limit. In this manuscript, we present a scalable technique wherein Indium, a low-work-function metal, is diffused to contact a few-layered MoS2 flake. The technique exploits a smooth outflow of Indium over gold electrodes to make edge contacts to pre-transferred MoS2 flakes. We compare the performance of three pairs of contacts made onto the same MoS2 flake, the bottom-gold, top-gold, and Indium contacts, and find that the Indium contacts are superior to other contacts. The Indium contacts maintain linear I – V characteristics down to cryogenic temperatures with an extracted Schottky barrier height of ∼2.1 meV. First-principle calculations show the induced in-gap states close to the Fermi level, and the damage-free contact interface could be the reason for the nearly Ohmic behavior of the Indium/MoS2 interface. [ABSTRACT FROM AUTHOR]

Fermi-level pinning caused by the kinetic damage during metallization has been recognized as one of the major reasons for the non-ideal behavior of electrical contacts, forbidding reaching the Schottky–Mott limit. In this manuscript, we present a scalable technique wherein Indium, a low-work-function metal, is diffused to contact a few-layered MoS2 flake. The technique exploits a smooth outflow of Indium over gold electrodes to make edge contacts to pre-transferred MoS2 flakes. We compare the performance of three pairs of contacts made onto the same MoS2 flake, the bottom-gold, top-gold, and Indium contacts, and find that the Indium contacts are superior to other contacts. The Indium contacts maintain linear I – V characteristics down to cryogenic temperatures with an extracted Schottky barrier height of ∼2.1 meV. First-principle calculations show the induced in-gap states close to the Fermi level, and the damage-free contact interface could be the reason for the nearly Ohmic behavior of the Indium/MoS2 interface. [ABSTRACT FROM AUTHOR]

Spin transport properties of single rhenium phthalocyanine (RePc) and double-rhenium phthalocyanine (Re2Pc2) molecular devices with gold electrodes have been investigated by combining Density Functional theory and nonequilibrium Green's functions. It was found that the RePc molecular devices exhibited good spin filtration efficiency in the small bias range even in the absence of magnetic electrodes. The Re2Pc2 molecular device exhibited a large magnetoresistance and excellent spin-filtering properties at a finite bias, which can only be achieved by altering the magnetization orientation of the rhenium atom at the center of the phthalocyanine molecule. These conclusions of the rhenium phthalocyanine molecule may have potential application in magnetoresistive devices and spin filters. [ABSTRACT FROM AUTHOR]

Metal oxide-based sensors have the benefit of inexpensive, quick response, and high sensitivity in detecting specific biological species. In this article, a simple electrochemical immunosensor was fabricated using antibody-chitosan coated silver/cerium oxide (Ab-CS@Ag/CeO2) nanocomposites on a gold electrode for sensitive alpha-fetoprotein (AFP) diagnosis in human serum samples. Successfully synthesis of AFP antibody-CS@Ag/CeO2 conjugates was confirmed through Fourier transform infrared spectra of the prototype. The amine coupling bond chemistry was then used to immobilize the resultant conjugate on a gold electrode surface. It was observed that the interaction of the synthesized Ab-CS@Ag/CeO2 nanocomposites with AFP prevented an electron transfer and reduced the voltammetric Fe(CN)63−/4− peak current, which was proportional to the amount of AFP. The linear ranges of AFP concentration were found from 10−12–10−6 g.ml−1. The limit of detection was calculated using the calibration curve and came out to be 0.57 pg.ml−1. The designed label-free immunosensor successfully detected AFP in human serum samples. As a result, the resulting immunosensor is a promising sensor plate form for AFP detection and could be used in clinical bioanalysis. [ABSTRACT FROM AUTHOR]

In the present study, a novel sensor PVA capped Mn doped ZnS incorporated MoS2 nanosheet composite modified gold electrode (PVA-Mn:ZnS/MoS2@GE) has been developed for the determination of acebutolol (ACB). Cyclic voltammetry (CV) and square wave voltammetry (SWV) were used to measure the electrochemical performance of ACB. When nanocomposite PVA-Mn:ZnS/MoS2 was used as a modifier in electrode-based sensors, results in well-resolved peaks and improved electrochemical current sensitivity compared to bare gold electrode. Using the SWV technique in pH 7.0 phosphate buffer, the examination of samples of biological, environmental and tablet spiked with ACB was monitored, the limit of detection and quantification is found to be 0.38 x 10-9 M and 1.28 x 10-9 M respectively. CV, energy dispersive X-ray, scanning electron microscopy, and impedance spectroscopy were performed to characterize the electrode material. A suitable mechanism was proposed for the number of protons and electrons involved in the redox reaction of ACB. [ABSTRACT FROM AUTHOR]

Au-n-octanedithiol-Au molecular junction (Au-SC8S-Au) has been investigated using density functional theory combined with the nonequilibrium Green's function approach. Theoretically calculated results are used to build the relationship between the interface binding structures and single-molecule quantum conductance of n-octanedithiol (SC8S) embodied in a gold nanogap with or without stretching forces. To understand the electron transport mechanism in the single molecular nanojunction, we designed three types of Au-SC8S-Au nanogaps, including flat electrode through an Au atom connecting (Model I), top-pyramidal or flat electrodes with the molecule adsorbing directly (Model II), and top-pyramidal Au electrodes with Au atomic chains (Model III). We first determined the optimized structures of different Au-SC8S-Au nanogaps, and then predicted the distance-dependent stretching force and conductance in each case. Our calculated results show that in the Model I with an Au atom bridging the flat Au (111) gold electrodes and the SC8S molecule, the conductance decreases exponentially before the fracture of Au–Au bond, in a good agreement with the experimental conductance in the literature. For the top-pyramidal electrode Models II and III, the magnitudes of molecular conductance are larger than that in Model I. Our theoretical calculations also show that the Au–Au bond fracture takes place in Models I and III, while the Au–S bond fracture appears in Model II. This is explained due to the total strength of three synergetic Au–Au bonds stronger than an Au–S bond in Model II. This is supported from the broken force about 2 nN for the Au–Au bond and 3 nN for the Au–S bond. [ABSTRACT FROM AUTHOR]

The adsorption of analyte molecules on nano-optoelectrodes (e.g. a combined nanoantenna and nanoelectrode device) significantly affects the signal characteristics in surface-enhanced Raman scattering (SERS) measurements. Understanding how different molecules adsorb on electrodes and their electrical potential modulation helps interpret SERS measurements better. We use molecular dynamics simulations to investigate the adsorption of prototypical analyte molecules (rhodamine 6G and choline) on gold electrodes with negative, neutral, and positive surface charges. We show that both molecules can readily adsorb on gold surfaces at all surface charge densities studied. Nevertheless, the configurations of the adsorbed molecules can differ for different surface charge densities, and adsorption can also change a molecule’s conformation. Rhodamine 6G molecules adsorb more strongly than choline molecules, and the adsorption of both molecules is affected by electrode charge in 0.25 M NaCl solutions. The mechanisms of these observations are elucidated, and their implications for voltage-modulated SERS measurements are discussed. [ABSTRACT FROM AUTHOR]

First time in the literature, we imprinted 8-hydroxyguanosine (8OHG) to engineer an impedimetric sensor on a polymer from three different main non-covalent structures. Considering the chemical structure of the molecule and its potential non-covalent bonding behaviors, we designed a special electrode with molecular imprinting technology (MIT). Therefore, 8OHG, which serves as an important biomarker of oxidative stress, was imprinted on an electrode to form an 8OHG sensor. In this imprinting method, firstly, a gold electrode was modified with Cytosine-1yl-acetic acid (CAA) to increase selectivity and form DNA hydrogen bond-like structures. Afterward, pyrrole and aminophenyl boronic acid monomers were polymerized from three different points by electropolymerization, and a selective and sensitive sensor technology was developed. 8OHG measurement was carried out impedimetrically in six minutes (R² value in the range of 500-10000 pg ml-1 is 0.9928 ± 0.006). LOD and LOQ was calculated 155.8 pg ml-1 and 472 pg ml-1, respectively. In conclusion, a sensitive, low-cost, fast and innovative technique with higher selectivity has been introduced. We believe that novel imprinting techniques will provide the important potential for MIP techniques for medical diagnostics. [ABSTRACT FROM AUTHOR]

To investigate the potential dependence of the dynamics of the interface structure of an ionic liquid (IL), electrochemical surface plasmon resonance (ESPR) has been combined with normal pulse and differential pulse techniques at the gold electrode interface of 1-butyl-3-methylimidazolium bis(trifluoromethanesulfonyl)amide. The fast response of SPR angle in 0.1 ∼ 0.2 s, originating from the orientation, distortion, and electronic polarization of ions in the first ionic layer, has been clearly observed, which is opposite to both the direction of the change in potential and of the slow response. This separate detection of the fast and slow responses has been realized based on the fact that the ionic rearrangement, which results in the slow response, does not proceed in a short potential pulse, especially for the positive pulse. The fast response, which reflects the interfacial dielectric constant, exhibits the potential-dependent dielectric saturation, i.e., a bell shape (or camel shape) potential dependence with a maximum around the potential of zero charge (PZC) and steep decrease at the potentials far from PZC. Molecular dynamics simulation explains that the decrease is caused by the strong electric field and ionic crowding in the first ionic layer which hinders the orientation and distortion of ions. [ABSTRACT FROM AUTHOR]

Sensitivity and selectivity are two important figures of merit in analytical measurements, but in redox potentiometry, they are often limited. In this study, we describe how the potentiometric sensitivity and selectivity can be improved using nanoporous gold (NPG) electrodes with hydrogen peroxide, dopamine, ascorbic acid, and a mixture of dopamine and ascorbic acid as the test analytes. The results show that the addition of platinum (Pt) to the nanoporous framework significantly improves electrode sensitivity for the analytes studied. Furthermore, it was only possible to potentiometrically detect hydrogen peroxide at the NPG-Pt electrodes. To further improve sensitivity and also impart some selectivity, the electrodes were spin-coated with Nafion. The addition of Nafion shifts the open-circuit potential to more positive values, increases sensitivity by almost a factor of 2, and imparts selectivity to the surface for the analysis of mixtures. Collectively, this works shows the promise of Pt-decorated nanoporous electrodes coupled with a Nafion film to improve the overall performance of redox potentiometry in analytical science. [ABSTRACT FROM AUTHOR]

Sandwich type voltammetric immunosensors were developed for the quantitative determination of cancer biomarkers, HER2 (human epidermal growth factor receptor 2), and CA125 (cancer antigen 125). Specific antibodies were immobilized on the gold electrodes by using a self-assembled monolayer of mercaptoundecanoic acid (MUA) activated by EDC-NHS ((1-ethyl-3-(3-dimethylamino propyl) carbodiimide and N-hydroxysuccinimide). Antibody conjugated gold nanoparticles decorated reduced graphene oxide (anti-HER2-Au/rGO and anti-CA125-Au/rGO) were used as enzyme-free nano labels for signal amplification. The sensors were characterized thoroughly by spectroscopic, microscopic, and electrochemical methods. Differential pulse voltammetric (DPV) studies in the presence of thionine revealed that the current signal produced is directly related to the biomarker concentration. A linear range of 0.2 pg ml-1 to 100 ng ml-1 was obtained, which indicated the immunosensors to be highly sensitive in lower concentrations of cancer biomarkers. Finally, the fabricated immunosensors were tested with serum samples spiked with HER2 and CA125. The results obtained from the test confirmed the data collected from clinical labs. [ABSTRACT FROM AUTHOR]

While gold is a stable metal in water, it is not uncommon for microfluidic experimenters using biologically-relevant fluids such as phosphate-buffered saline (PBS) to witness their precious gold electrodes quickly vanish from the microchannel once the voltage exceeds a few volts. This stability issue concerns multiple fields where high voltage provides superior actuator or sensor performance, such as resistive pulse sensing (RPS), electroosmosis, electrowetting and so on. One solution to protect metallic electrodes is using alternative voltages (AV) as opposed to continuous voltages. After recalling that gold dissolution is enabled by the chloride ions present in most biologically-relevant solutions, we explore the stability conditions of the electrodes for voltages from 1 to 20 Vpp (Peak to Peak voltage amplitude), actuation frequencies between 0 and 5 kHz, and for various pH and electrolytes (NaCl, Na2SO4, HCl). We find that the dissolution threshold voltage depends on the ratio of reaction to diffusion rate given by the Damkhöler number Da. In mass-transfer limited regime, the dissolution threshold is independent of the frequency, whereas the dissolution voltage is observed to grow as Da-1/2 in the reaction limited regime. These findings provide guidelines to design more reliable electrowetting, electroosmosis, dielectrophoresis and resistive pulse sensing devices. [ABSTRACT FROM AUTHOR]

Plasma contacting with liquid (PCL) provides many charged particles and reactive species into the liquid. The difficulty in controlling or selecting each specific species has significantly limited its applications in industry. Here, we present a study on using voltage polarity to regulate the type of charged particles absorbing from the plasma into the liquid. A detailed understanding of the processes at the plasmaâ€"liquid interface and electrolysis due to switching in voltage polarity was determined via a visual pH observation, measuring the concentration of H2O2 and solvated electrons. The results indicated that changes in voltage polarity strongly affect the plasma properties, chemical properties and electrolysis process in liquid, and also in the types of reducing species for gold nanoparticle (GNP) synthesis. The results also showed that using a suitable frequency could improve the efficiency of absorption of H2O2 from plasma into the bulk liquid as well as the yield in the production of GNPs. The results provide a way to select desired species from the plasma to be transferred into the liquid for a distinct purpose and to accompany other properties in the system of PCL. [ABSTRACT FROM AUTHOR]

The organoleptic virtues of wine can be damaged by the presence of compounds produced during fermentation or aging, such as mercaptans. This work presents an environmentally friendly electrochemical sensor for the easy detection of mercaptans in wine samples, using glassy carbon and screen-printed carbon electrodes. The modification of the carbon working electrodes with gold nanoparticles increased the sensitivity and selectivity of the procedures, considering the strong covalent bond that forms readily between sulfur and gold atoms. Ethanethiol reduction has been shown to depend both on pH and on adsorption time since the electrode is immersed in the solution until the voltammogram is recorded. The highest current has been recorded in a supporting electrolyte solution at pH 4.2 with an adsorption time of 10 min in the case of gold nanoparticle modified glassy carbon electrodes and pH 3 and 90 s for gold nanoparticle screen-printed carbon electrodes. The developed procedures reach a reproducibility of 7.9% (n = 7), based on the slopes associated with different calibration curves registered in the concentration range from 7.7 to 36.6 μg l-1 when using gold nanoparticle modified glassy carbon electrodes and 7.2% (n = 5) in the case of gold nanoparticle modified screen-printed carbon electrodes (concentration range, from 1.6 to 10.9 μg l-1). The sensors have successfully been applied to the detection of ethanethiol, representing mercaptans, in white and red wines. [ABSTRACT FROM AUTHOR]

Narrow bandgap semiconductors like indium antimonide (InSb) are very suitable for high-performance room temperature infrared photodetectors, but the fragile nature of the wafer materials hinders their application as flexible/wearable devices. Here, we present a method to fabricate a photodetector device of assembled crystalline InSb nanowire (NW) arrays on a flexible substrate that balances high performance and flexibility, facilitating its application in wearable devices. The InSb NWs were synthesized by means of a vapor–liquid–solid technique, with gold nanoclusters as seeding particles. The morphological and crystal properties were investigated using scanning electron microscopy, x-ray diffraction and high-resolution transmission electron microscopy, which revealed the unique spike shape and high crystallinity with (111) and (220) planes of InSb NWs. The flexible infrared photodetector devices were fabricated by transferring the NWs onto transparent and stretchable polydimethylsiloxane substrate with pre-deposited gold electrodes. Current versus time measurement of the photodetector devices under light showed photoresponsivity and sensitivity to mid-infrared at bias as low as 0.1 V while attached to curved surfaces (suitable for skin implants). A high-performance NW device yielded efficient rise and decay times down to 1 s and short time lag for infrared detection. Based on dark current, calculated specific detectivity of the flexible photodetector was 1.4 × 1012 Jones. The performance and durability render such devices promising for use as wearable infrared photodetectors. [ABSTRACT FROM AUTHOR]

The asynchronous transient responses at the edge and center of a gold disk electrode are monitored by in situ differential reflectance spectroscopy (DRS). The DRS spectrum collected in 10 mM perchloric acid shows that the edge of the electrode achieves the equilibrium sooner than the center does in chronoamperometry, which establishes the foundation for a similar electrochemical protocol to remove the metallic Cu at the edge of a Cu/Au disk electrode while keeping these at the center intact. Both phenomena are caused by the larger resistance at the center than the edge of a disk electrode. [ABSTRACT FROM AUTHOR]

Ionic liquids (ILs) add complexity to electrochemical interfaces that cannot be adequately treated with traditional double layer models. We present a series of carefully controlled capacitance measurements to optimize the collection of reproducible and uniform capacitance-potential datasets. We quantitatively evaluate analysis methods on the experimentally observed capacitance of l-ethyl-3-methylimidazolium trifluoromethauesulfonate [Emim][TFO] IL at the gold-IL interface. The major outcomes of our work are to identify how experimental data collection methods affect capacitive hysteresis, and to suggest a systematic approach to collect reproducible capacitance data for IL systems. We evaluate different potential scan directions, examine varying potential sweep rates, and capacitance collection methods. We find that faster scan rates can mitigate the capacitive hysteresis between the anodic and cathodic scans for a particular collection technique. However, faster scan rates also result in more variation between the collection techniques. We also find that decreasing the effective potential sweep rate reduces hysteresis between different collection techniques when other factors are held constant. It is crucial for researchers to consistently report the direction of the potential sweep and the effective rate of potential sweep. Our data suggest that using slower effective potential perturbation rates would reduce discrepancies in capacitance data collected from different laboratories under different experimental conditions. [ABSTRACT FROM AUTHOR]

Despite significant demand for penetrating intracortical neural probes (PINPs), challenges remain regarding their biocompatibility and stability due to the mechanical mismatch between brain tissue and PINPs. Here, we propose a promising UV patternable polymeric material for PINPs and a design criterion for optimizing the geometry of polymeric PINPs. UV-curable polysiloxane acrylate (PSA) shows remarkably low cytotoxicity in vitro, comparable to that of polyimide. Real-time two-photon imaging of CX3CR1-gfp-Tg mice reveals that a PSA microneedle shows a markedly low immune-responsive effect. The photo-patternability and modulus-tunability of PSA provide effective design capability, even for hierarchical structures. Also, we found a design criterion suggesting minimized scar that can penetrate the tissue surface, reducing both iatrogenic injury and mechanical mismatch while simultaneously dampening tissue micromotion. This damping behaviour of polymeric PINPS was shown by both experimental methods and finite element method simulation. Finally, we fabricated gold electrodes on PSA microneedles and successfully recorded local field potentials during seizure activity. [ABSTRACT FROM AUTHOR]

Due to increased energy demand and environmental concerns, sustainable energy systems such as electrolyzers and Li-air batteries have attracted significant interest. However, it is imperative to develop an efficient inexpensive catalyst for the underlying reactions, namely oxygen reduction (ORR) and evolution (OER) reactions, to overcome their sluggish kinetics. In our previous work, a combination of silver and Co3O4 particles showed high bifunctional activity. Herein, we extend the study to investigate how the electrocatalytic activity is dependent on the oxide composition and the type of the underlaying substrate. A significant enhancement in OER performance is realized at perovskite-supported silver or gold electrodes with activity decreasing in the order Ag≥Au>GC. This is attributed mainly to a synergistic interaction between the oxide and metal support and the enhanced conductivity. The ORR activity observed at oxides loaded on Ag and Au bulk electrode is similar, however they exhibit about 450 mV lower overpotential than on GC. The improved activity at oxides/metal substrate renders this approach promising for O2-electrodes design. [ABSTRACT FROM AUTHOR]

Graphene nanoribbon is an attractive material for nano-electronic devices, as their electrical transport performance can be controlled by their edge structures. However, in most cases, the electrical transport has been investigated only for graphene nanoribbons fabricated on a substrate, which hinders the appearance of intrinsic electrical transport due to screening effects. In this study, we developed special devices based on silicon chips for transmission electron microscopy to observe a monolayer graphene nanoribbon suspended between two gold electrodes. Moreover, with the development of an in-situ transmission electron microscopy holder, the current–voltage characteristics were achieved simultaneously with observing and modifying the structure. We found that the current–voltage characteristics differed between 1.5 nm-wide graphene nanoribbons with armchair and zigzag edge structures. The energy gap of the zigzag edge was more than two-fold larger than that of the armchair edge and exhibited an abrupt jump above a critical bias voltage in the differential conductance curve. Thus, our in-situ transmission electron microscopy method is promising for elucidating the structural dependence of electrical conduction in two-dimensional materials. [ABSTRACT FROM AUTHOR]

Designing tunable molecular devices with different charge carriers in single-molecule junctions is crucial to the next-generation electronic technology. Recently, it has been demonstrated that the type of charge carriers depends on and can be tuned by controlling the molecular length and the number of interfacial covalent bonds. In this study, we show that the type of charge carriers can also be tuned by controlling the material and shape of electrodes. N-heterocyclic carbenes (NHCs) have attracted attention because of their ability to form strong, substitutional inert bonds in a variety of metals. Also, NHCs are more stable than the widely used thiol group. Therefore, we use electrodes to tune the type of charge carriers in a series of NHCs with different side groups. The ab initio calculations based on non-equilibrium Green's formalism combined with density functional theory show that the dominant charge carrier switches from electrons to holes when gold electrodes are changed into platinum ones. The nature of the charge carriers can be identified by variations in the transport spectra at the Fermi level (EF), which are caused by the side groups. The projections of transport spectra onto the central molecules further validate our inferences. In addition, the transmission coefficient at EF is found to be dependent on the atomic interface structure. In particular, for the NHC without methyl or ethyl side groups, connecting a protruding atom on the electrode surface significantly enhances the transportability of both electrode materials. Overall, this study presents an effective approach to modifying transport properties, which has potential applications in designing functional molecular devices based on NHCs. [ABSTRACT FROM AUTHOR]

An electrochemical sensor based on Au/poly(ortho-aminophenol-co-ortho-phenylenediamine)/TiO2 nanocomposite ((Au/P(OAP-co- OPD)/TiO2)) to detect ampicillin (AMP) antibiotic was developed. The thin films of poly(ortho-aminophenol) (POAP), poly(orthophenylenediamine) (POPD), P(OAP-co-OPD), POAP/TiO2, POPD/TiO2 and (P(OAP-co-OPD)/TiO2)) nanocomposites were synthesized on gold electrodes by in situ electrocopolymerization method and characterized by CV, FT-IR, SEM, EIS, in situ resistivity measurements and in situ UV-visible spectroelectrochemistry. Two mechanism for copolymerization of OAP and OPD were suggested. In order to achieve a reproducible state of the sensing, the current changes were recorded for nanocomposites electrodes over time using the double chronoamperometric technique. Between the modified electrodes, Au/(POAP-co-POPD)/TiO2 nanocomposite exhibited high conductivity and sensitivity, excellent activity and long-term stability for detecting AMP antibiotic with a limit of detection down to 0.28 nM. The reproducibility of the Au/Cop. A/TiO2 nanocomposites sensors to lowest AMP concentration contents was observed approximately 6%-8% changes. The interference effects of four selected antibiotics on AMP for Au/Cop. A/TiO2 nanocomposites electrode were investigated. The response signal indicating that the sensor can not detect the target molecules within the different concentration range solutions. The results in the analysis of AMP on Au/P(OAP-co-POPD)/TiO2 sensor demonstrates that the obtain electrode is suitable as a promising candidates for electrochemical sensor applications. [ABSTRACT FROM AUTHOR]

A non-enzymatic electrocatalyst, nickel oxide (NiO) nanosheets was developed via a facile hydrothermal approach and further characterized in detail. To harness the potential of NiO nanosheets as a potential electrocatalyst, the hydrothermally synthesized nanosheets were fixed onto the sensor working electrode for glucose sensing application. The NiO nanosheets providing abundance active sites for non-enzymatic glucose detection showed sensitive (1618.4 µA mM-1 cm-2) response in the linear range of 0.25-3.75 mM. The excellent electrocatalytic activity of the NiO modified gold working electrode resulted in a low detection limit (2.5 µM). Moreover, the sensor selectively detected glucose in the solution containing common interferants such as cholesterol, dopamine, uric acid and ascorbic acid, further makes it highly suitable for non-enzymatic glucose detection in near-real samples. [ABSTRACT FROM AUTHOR]

It is very simple and convenient using the commercial chloroauric acid instead of sodium gold sulfite as the main salt in the Au(I) sulfite electrodeposition bath. In this paper, the effects of chloride ions on cyanide-free Au(I) electrodeposition in the gold sulfite bath are carefully investigated. Both UV-vis absorption spectroscopy and visual inspection reveal that chloride ions suppress the disproportionation reaction of Au(I) and improve the bath stability. Cyclic voltammetry indicates that chloride ions promote the cathodic reduction of Au(I). EC-SERS spectra elucidate that in the sodium sulfite solution, SO3 2- ions firstly adsorb on the gold electrode, then experience a structural transformation (SO3 2- S2O5 2-), and last electroreduce to S2O3 2- ions (S2O5 2- S2O3 2-) as the potential shifts negatively. In the gold sulfite electrolytes, the cathodic reduction of Au(I) and chloride ions hinder the reduction of S2O5 2- ions. The gold coatings obtained from the gold sulfite electrolyte containing chloride ions present in fine and pure grains without chlorine and sulfur inclusion. [ABSTRACT FROM AUTHOR]

We demonstrate a novel method for the selective extraction and electrochemical detection of S100β disease biomarker. The protein is extracted from blood plasma using target-specific gold coated magnetic nanoparticles. This is followed by the rapid reduction of the disulfide bond structure of the purified protein using chronoamperometry and its immobilisation onto a nanostructured gold electrode. The protein concentration is quantified down to 10 pM (120 ng l−1 ), by electrochemical desorption using differential pulse voltammetry (DPV). The new method was used to extract and determine S100β in spiked blood plasma and the DPV quantification was cross-validated against enzyme-linked immunosorbent assay (ELISA) where the percent agreement between the two measurements was 96.54%. Therefore, this method has strong potential for the sensitive determination of S100β. In addition, 65% of proteins have similar disulfide bond structure. Therefore, the new method can be utilised for the determination of many disease biomarkers after optimizing specific extractor nanomaterial for the target biomarker. [ABSTRACT FROM AUTHOR]

A facile way was developed to fabricate Zr(IV) cation modified gold electrode for high-performance electrochemical sensing of methyl parathion (MP) via layer-by-layer self-assembly. The electrode was prepared by sequentially absorbing 11-mercaptoundecyl-phosphoric acid (MDPA) and Zr(IV) cation on gold electrode through strong chelating interactions between gold and -SH as well as Zr(IV) cation and phosphoric groups of MDPA. Fourier transform infrared spectrophotometry, field-emission scanning electron microscopy, energy-dispersive X-ray spectroscopy and cyclic voltammetry were employed for the characterization of morphologies and electrochemical properties. The sensor was used to determine MP by square wave voltammetry. The cathodic peak current (at + 0.25 V vs saturated calomel electrode) increases linearly in the range of 1.0 - 180.0 ng ml-1 under optimized conditions. And the detection limit is low to 0.22 ng ml-1 (based on a signal-to-noise ratio of 3). The electrode is successfully used to detect MP in the real water sample with recoveries of 98.97%-102.4% and RSDs of 0.21%-1.99% (n = 3) at three spiked levels. The proposed method provides one simple way to prepare Zr(IV) cation modified electrode for the fast determination of MP. The reliability and accuracy of the method is validated by independent assays with HPLC. [ABSTRACT FROM AUTHOR]

Prussian blue (PB) modified nanoporous gold (NPG) electrodes exhibit great potential for improving the detection sensitivity and stability for hydrogen peroxide monitoring. The NPG provides large surface-to-volume ratio as well as diffusion 'highways' to assist the transfer of the ions. In the present work, we optimized the deposition time for NPG fabrication and examine the electrochemical performance of the electrodes. A critical deposition time on the electrochemical performances including linear range, operational stability and sensitivity was experimentally determined. Below and above such a deposition time, two different growth patterns of the microstructures were observed. This transition of deposited structures corresponding to the critical time results in different pathways for electron transfer and ion diffusivity through PB lattice. [ABSTRACT FROM AUTHOR]

Lysozyme is an enzyme that is responsible for the catalysis of β - 1,4 bond breakage in peptidoglycan residues of Gram-positive bacterium cell walls between N-acetylmuramic acid and N-acetylglucosamine. Lysozyme is commonly applied in food industry and its elevated concentration might indicate a development of leukemia or kidney failure, hence it is necessary to elaborate fast and sensitive tools for its detection. Herein, we present the studies on the elaboration of electrochemical aptasensor for lysozyme determination. For that purpose thiolated aptamer probes were immobilized on gold electrode surface that was subsequently modified with 6-mercapto-1-hexanol as blocking agent. It was found that 2h incubation period is sufficient to form monolayers that efficiently bind to target analyte. Methylene blue at 2 μM concentration was chosen as redox indicator as it provided the highest biosensor response in comparison to other tested electroactive molecules. 5 min. incubation time enabled lysozyme detection within the range from 0.1 fM to 10 nM. The developed biosensor exhibited good selectivity toward target analyte as well as minor response toward a reference DNA aptamer specific for HER2 biomarker. The proposed sensor was also successfully used for discrimination of lysozyme in diluted serum samples. [ABSTRACT FROM AUTHOR]

Gold electrode (GE) is modified with composite of Au nanoparticles (AuNPs) and graphene quantum dots (GQDs), and its electrochemical performance is evaluated. The modified electrode (GE/AuNPs/GQDs) exhibits higher electrochemical activity and better stability than bare GE and AuNPs or GQDs modified GEs. The higher electrochemical activity of GE/AuNPs/GQDs is attributed to the increase of the active surface area and the decrease of the interface transfer resistance that accelerates reactant absorption and electron transfer of the electrodes. In addition, p-p interaction between GQDs in theGE/AuNPs/GQDs and aromatic rings of phenolic compounds contributes to the enhanced electrochemical activity in detection of phenolic compounds. Given the high electrochemical activity and long cycling stability, the method for GE modification can be applicable to the detection of phenolic compounds. [ABSTRACT FROM AUTHOR]

By introducing Cu into the self-assembled curcumin-cysteine on gold electrode, the surface reactivity has been tuned by potentiodynamic electrodeposition approach. The synthesis of curcumin-cysteine has been carried out by modified Fischer esterification method and confirmed by FT-IR, ¹H, and 13C NMR spectroscopy, respectively. The self-assembly of curcumin-cysteine on gold electrode has been confirmed by electrochemical techniques like, cyclic voltammetry and electrochemical impedance spectroscopy (EIS). The surface confinement of modular copper nanospheres and its bi-dentate complexation with the diketo moiety of self-assembled curcumin-cysteine is enhancing the catalytic activity. Further, as-constructed electrochemical platform has been exploited for electrocatalytic application like: electroreduction of p-nitrophenol and also tested for real world sample analysis. The fabricated sensor has shown an enhanced sensitivity (i.e, 153.08 μAμM-1cm-2) and low level of detection (i.e, 57 nM) of p-nitrophenol as well as good selectivity in the presence of interfering species. The present investigation is providing an ideal approach for resource limited settings to construct an economically viable sensor and molecular electronic devices. [ABSTRACT FROM AUTHOR]

A variety of voltammetric methods have been carried out for determination of brexpiprazole (BRX) using cyclic voltammetry (CV) and two different type anodic stripping methods; differential pulse (AS-DP) and square wave (AS-SWV) at modified carbon paste electrode with gold nanoparticles (AuNPs-CPEs). Additionally, electrochemical impedance spectroscopy (EIS) technique has been utilized for characterization of the different electrodes. Electrochemical oxidation behavior of BRX shows an irreversible anodic peak at 0.88 V versus Ag/AgCl, in Britton-Robinson buffer (BR) at pH 4.0, 50s preconcentration time and -0.5 deposition potential. Rectilinear relationship between the peak current versus concentration was obtained over the ranges of 1.32 × 10-6-6.45 × 10-6 and 1.32 × 10-7- 6.45 × 10-7 mol L-1 for AS-DP and AS-SWV respectively. The lowest concentration that can be detected for both for AS-DP and AS-SWV was 3.99 × 10-7 and 3.32 × 10-8 mol L-1 respectively; the utilized methods have been devoted adequately for the estimation of BRX in its pure and dosage form. [ABSTRACT FROM AUTHOR]

Fast and accurate measurement of hydrogen peroxide is essential to glucose monitoring. In this work, we describe a highly efficient H2O2 sensor through the modification of Prussian blue (PB) on the nanoporous gold film (NPG). By de-alloying from Au-Ag film, we prepare the NPG film and characterize it through SEM and AFM. Tests using chronoamperometry and cyclic voltammetry on the Prussian blue modified NPG electrodes show an excellent electrochemical performance of the sensors. Owing to the comparatively huge specific surface area in the nanoporous structure, such electrodes significantly enhance the direct electron transfer from PB nanocrystals to NPG film. Comparing to earlier PB modified electrodes, the sensor fabricated in this work exhibits the widest linearity of 0.001~17 mM, and produces a high selectivity of 708 µA·cm-2·mM-1. [ABSTRACT FROM AUTHOR]

The effect of instabilities on the nonlinear electrochemical impedance spectroscopic (NLEIS) response of a simple electron transfer reaction in a kinetic and diffusion-controlled regime was studied using classical Fe2+/Fe3+ redox couple on a gold electrode. Numerical simulations were employed to calculate the NLEIS response, and the predictions were compared with experimentally acquired NLEIS data. Instabilities were introduced by continuously changing the dc potential or the active species concentrations. At high frequencies, the effect of potential instabilities manifested more clearly in higher harmonic signals than at the fundamental frequency. In case of changes in species concentrations which did not break the symmetry, the higher harmonics were not particularly more sensitive than the fundamental. An analysis of the results shows that multiple factors contribute to the higher harmonics. The sensitivity of second harmonics to the instabilities arises from the nonlinear component of the rate constant as well as the interaction between the rate constant oscillations and concentration oscillations at the applied frequency. The results show that NLEIS can be used to quickly identify instabilities which alter the symmetry. [ABSTRACT FROM AUTHOR]

In this work, we have studied tin electrodeposition on polycrystalline gold electrodes from two different supporting electrolytes: sulfuric acid (SA) and methanesulfonic acid (MSA), both of them commonly used in the industry. This work aims to understand the effect of the different electrolyte anions on the deposition process. We show at least three different tin deposition mechanisms on gold: irreversible adsorption, underpotential deposition, and overpotential (bulk) deposition. Underpotential deposition leads to the formation of a layer of tin in SA and MSA with a coverage around θSn(H2SO4) = 0.45 ML (monolayer) and θSn(CH3SO3H) = 0.42 ML, respectively. The UPD Sn layer is however somewhat uncharacteristic as it is associated with island formation and surface alloying. Cyclic voltammograms in an extended potential range showed five distinct peaks: two cathodic peaks associated with tin underpotential and overpotential deposition, and three main anodic peaks, corresponding to the oxidation of the bulk Sn, of the AuSn intermetallic layer, and of the adsorbed Sn(II) to Sn(IV). Both voltammetric and rotating disk electrode measurements show that the kinetics of tin electrodeposition in MSA is slower than in SA, which we ascribe to Sn-MSA complex formation in solution. Slow Sn deposition in MSA promotes AuSn formation, in contrast to SA in which bulk tin deposition is more prominent. Complete Levich-type mass transport control of tin deposition in SA and MSA was only reached at low scan rate due to concurrent HER on the uncovered gold surface during the deposition process at higher scan rates. An unexpected surface-confined passivation process is observed in both electrolytes. [ABSTRACT FROM AUTHOR]

A selective and sensitive electrochemical sensor for detecting uric acid (UA) has been developed. The UA electrochemical sensor was made from single-walled carbon nanotubes (SWCNTs), which were coated on the surface of a gold wire electrode using the chemical vapor deposition (CVD) method. The performance of UA electrochemical sensor was characterized using cyclic voltammetry. The obtained calibration curve followed a linear equation, ipa = 132.753 + 1.512c, with R2 = 0.99597. The LOD and sensitivity of the SWCNTs-modified gold electrode for UA detection obtained were 5.05 nM and 5.240 μA mm-2nM-1, respectively. The reaction between the electrode and UA demonstrated the diffusion-controlled behavior. No interference signals from ascorbic acid, glucose and urea were observed during the UA measurements. However, the signal for dopamine appeared in the voltammogram, although it was located at a different potential. Moreover, the dopamine signal disappeared when the measurement was conducted at concentrations of less than 1 mM. These results confirm that SWCNTs-modified gold electrodes are favorable for detecting uric acid. [ABSTRACT FROM AUTHOR]

The adsorption kinetics and thermodynamics of hydroquinone (QH2) onto a polycrystalline gold electrode surface in an unbuffered aqueous solution as a function of concentration have been investigated using cyclic voltammetry. The adsorption kinetics appeared to be kinetic control rather than diffusion control. The adsorption thermodynamics was represented by the Langmuir isotherm as the interaction parameter of the Frumkin isotherm was found to be 0.01, indicating small interaction between the adsorbate molecules. The saturation surface coverage was found to be 1.8 × 10-10 mol cm-2 , which suggested that QH2 adsorbs on a polycrystalline gold electrode in horizontal orientation at the close packing state. The free energy of the adsorption was calculated to be -23 kJ mol-1, indicating moderate adsorption force. [ABSTRACT FROM AUTHOR]

Biomaterials gelatin is used as the dielectric layer in this work to develop metal/gelatin/Tungsten (W) RRAM devices, with silver (Ag), copper (Cu), W, and gold (Au) as the top electrode (TE) to study the effects of electrode metals on device characteristics. All types of the RRAM devices exhibit bipolar resistive switching characteristics with diverse performances. The work function difference between the TE and bottom electrode (BE) metals is found to play a profound role in determining the characteristics of the devices and even reversing the set and reset processes. The devices with larger work function difference between the TE and BE metals have higher and more stable on/off resistance ratio. The Ag/gelatin/W devices exhibit a relatively stable switching behavior with an on/off resistance ratio of >102, while that with Au TE exhibits a reversed set and reset processes with a high on/off resistance ratio of >105 owing to the large positive work function difference between Au and W. Metallic conductive filaments are confirmed to be responsible for the switching behaviors of the devices experimentally, and what metal element in the conductive filaments is determined by the work function difference of the metals used for the top and bottom electrodes. [ABSTRACT FROM AUTHOR]

This paper reports on the electrochemical characterization and comparison of printable silver inks for the fabrication of planar electrodes to integrate in a microfluidic platform for in situ desalination of seawater prior to detection of nutrients in marine environment. Screen printing and inkjet printing were investigated to overcome limitations of more conventional deposition techniques. The screen printed ink DuPont 5064H was chosen for the fabrication of the desalination platform as it displayed the best properties in terms of oxidation ability (15.5 mC/mm2) and absence of sample contamination. The platform was tested at different oxidation conditions; the optimum potential for desalination was found to be +0.9 V. The device desalination performance was then evaluated through conductivity measurements of the treated sample and a proof-of-concept was achieved: for a potential of +0.9 V, conductivity (hence concentration) could be lowered from an initial value of 42.13 mS (0.6 M) to 20.36 mS (0.206 M), 17.37 mS (0.157 M) and 6.38 mS (0.0516 M) for oxidation times of 120 s, 240 s and 360 s, respectively. The operating conditions allowed the regeneration of the silver electrode and the possibility to deploy it for six to ten cycles before depletion of the silver working electrode. [ABSTRACT FROM AUTHOR]

Adsorption of hydroquinone (QH2) onto a polycrystalline gold electrode surface in an unbuffered aqueous solution was confirmed by cyclic voltammetry (CV) and time-of-flight secondary ion mass spectrometry. The adsorption appeared to inhibit direct electron transfer between QH2 in the solution and the gold electrode. CV indicated that the surface coverage was ca. 9 × 10-11 mol cm-2. It was also demonstrated that when QH2 was electrochemically oxidized, the adsorbed QH2 likely desorbed from the gold surface. [ABSTRACT FROM AUTHOR]

A gold electrode (GE) modified with L-cysteine and gold nanoparticles (AuNPs) has been generated for computing the individual and simultaneous determination of nimesulide (NM) and acetaminophen (APAP). The electrochemical behavior of the pair of molecules has been inspected utilizing squarewave voltammetry (SWV), cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS). Studies indicated that the oxidation of APAP and NM is expedited at AuNPs/L-cysteine GE giving well defined peaks for APAP and NM at 0.596 V and 1.072 V respectively in Britton-Robinson (B-R) buffer (pH 2). The assay enabled simultaneous determination of these drugs in the linear working range of 3.0 × 10-4 M-1.0 × 10-5 M with detection limits of 4.06 × 10-7 M and 6.49 × 10-6 M for APAP and NM respectively. The high selectivity and sensitivity of the proposed assay were illustrated by its active application in the ascertainment of both APAP and NM in pharmaceutical preparations. [ABSTRACT FROM AUTHOR]

Electropolymerization of Azure A on indium-tin oxide (ITO) and gold electrodes have been carried out from KNO3 aqueous solution. After repetitive voltammetry cycles (electrochemical ageing process), surface morphology of the resulting film is altered involving a deactivation of its pristine electroactivity. Aged and pristine PAA films have been characterized by hyphenated techniques based on spectroelectrochemistry and electrogravimetry (cyclic voltammetry, electrochemical quartz crystal microbalance, and Vis-NIR spectroscopy). Correlation of these techniques allows to obtain the very subtle qualitative and quantitative difference between both films. Accumulation of hydrogen gas inside films is postulated to be the cause of the electrochemical deactivation. In addition, the electroactivity renovation by a soft thermal treatment in oven at 60°C during 24 h is evaluated. [ABSTRACT FROM AUTHOR]

Presented work studies the relation between kinetics of metal deposition via surface limited redox replacement (SLRR) of underpotentially deposited (UPD) monolayer (ML) and experimental parameters of reaction solution such as meal ions concentrations and supporting electrolyte concentration. The model system is Au deposition on Au(111) via SLRR of Pb UPD ML. The rate constant of the SLRR reaction for different solution designs is determined from temporal change of electrode surface reflectivity and from the open circuit potential transients' analysis. The obtained results show clearly that reaction kinetics of metal deposition via SLRR of UPD ML is significantly affected by the design of the reaction solution i.e. the UPD metal ion, depositing metal ion, and supporting electrolyte concentrations. The ten-fold change of concentration of either solution parameter produces approximately the same change in the value of the rate constants. The presented results have fundamental importance for the future development and application of the metal deposition via SLRR of UPD ML. They offer a link between the reaction solution design and expected trend in SLRR reaction rate, which transposes to successful control of deposition flux, nucleation density and resulting morphology of the deposit. [ABSTRACT FROM AUTHOR]

A channel flow triple electrode (CFTE) was employed for the in-situ detection of Fe2+ and Fe3+ preferentially dissolved from a Pt-50at.%Fe alloy under potential cycles in a 0.5 M H2SO4 solution. The CFTE consisted of a Pt-50at.%Fe alloy working electrode (PtFe-WE) and two split Au collector electrodes (Au-CE) placed upstream and downstream in a channel, respectively. The optimum potentials for detecting Fe2+ and Fe3+ on the Au-CEs were determined to be 1.0 and 0 V vs. a standard hydrogen electrode, respectively, when using solutions of different concentrations of FeSO4 and Fe2(SO4)3. When PtFe-WE was potential-cycled between 0.05 and 1.4 V, Fe dissolved as Fe2+ between 0.25 and 0.75 V in both anodic and cathodic scans, and mainly dissolved as Fe3+ above 1.1 V and from 0.9 to 0.5 V in cathodic scans. [ABSTRACT FROM AUTHOR]

In recent years, there has been a substantial increase in the research of plasmonic effects in catalysis motivated by the enhanced surface reactivity that can be achieved using resonant optical fields confined on the nanoscale. However, these plasmonic materials have not been extended to electrocatalysis applications. In this paper, we demonstrate the fabrication, modeling and characterization of gold (Au) nanofiber-based electrodes for plasmonic enhanced electrocatalysis of ethanol and methanol in alkaline media. By combining light scattering and electrochemical measurements with computational electromagnetic field design, we show that the resonant excitations of plasmon modes in Au nanofibers can significantly increase the activity of electrocatalytic reactions at electrode surfaces by preventing their passivation. In particular, our results demonstrate higher performance and stability of the alcohol electrocatalysts in sodium hydroxide solutions. The fabrication of "plasmonic electrodes" using the facile, inexpensive and environmentally friendly electrospinning technology provides unique opportunities to engineer novel light-enhanced electrodes over large surface areas for applications to fuel cells, electrofuels, and other electrolysis systems. [ABSTRACT FROM AUTHOR]

The electric double layer containing a negatively charged compact-layer surface was designed by modifying the 3-mercaptopropionic acid self-assembled monolayer (3-MPA SAM) on the Au electrode. Thus the surface potential of the compact layer on the SAM can be adjusted by shifting the dissociation equilibrium of the carboxyl group (-COOH). Cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS) were used to study the electrochemical reversibility of Fe(CN))6 at the above mentioned electrode, respectively. A key finding is that the negatively charged 3-MPA SAM surface can depress the electrochemical reversibility of Fe(CN))6, while the formation of ion-pairs between the dissociated carboxylate groups (-COO-) and the divalent cations on the monolayer can improve the electrochemical reversibility of Fe(CN))6 by increasing the surface potential of the compact layer. Further, the electrochemical reversibility of Fe(CN))6 can also be regulated by a mixed solution of different divalent cations. The logarithm of ion-pair formation constants (log K) with the -COO- were determined to be 2.78 ° 0.03, 2.75 ° 0.04, 2.69 ° 0.04 for Ba2+, Ca2+, Mg2+ by electrochemical titration method, respectively. [ABSTRACT FROM AUTHOR]

In the present study, we investigated the reduction and the evolution of oxygen from lithium containing DMSO based electrolytes at gold. The number of electrons that are transferred per O2 (z-value) during oxygen reduction depends on the structure of the electrode: Despite the presence of Li+, O2 is reduced electrochemically to superoxide at smooth gold electrodes and at low overpotentials. At porous electrodes a z-value close to 2 e-/O2 indicates Li2O2-formation even at low overpotentials. This is ascribed to a reaction of superoxide, which is catalyzed by gold-particles at open circuit. This behavior is also responsible for the non-proportionality between reduced and evolved amounts of oxygen. Furthermore, we observed a linear relationship between evolved amounts of CO2 and reduced amounts of oxygen, indicative for electrolyte decomposition during oxygen reduction. Combined electrochemical quartz crystal microbalance (eQCMB) and Differential electrochemical mass spectroscopy (DEMS) measurements reveal that mass changes that occur in the anodic sweep are due to the evolution of CO2, whereas oxygen evolution takes place without any mass changes. The observed m.p.e-values (mass changes per transferred electron) are affected by convection due to the formation of soluble reduction products which observed in rotating ring disc electrode measurements. [ABSTRACT FROM AUTHOR]

Simple and label-free electrochemical sensors for the detection of DNA hybridization were developed based on charge perturbation of poly(thionine)-modified glassy carbon and gold electrodes (PTH/GCE and PTH/Au). Probe DNA (pDNA) was immobilized on PTH films via covalent bonds between the amine (-NH2) group of the PTH and the phosphate (PO43-) group at the 5' end of the pDNA. The immobilized single-strand pDNA decreased the oxidation current of [Fe(CN)6]4- as a result of electrostatic repulsion by the negatively charged PO43- backbone of the pDNA. The current was further decreased subsequent to duplex formation by the hybridization of target complementary DNA (cDNA) due to increased electrostatic repulsion. Both sensors demonstrated excellent selectivity, stability, and the sensitivity of 1.27 and 58.6 µA⋅cm-2⋅pM-1 with detection limits of 0.47 and 0.20 pM, respectively, for cDNA hybridization. [ABSTRACT FROM AUTHOR]

In this paper, a novel electrochemical sensor based on thiol-β-cyclodextrin (β-CD-SH) and graphene (GR) hybrid-modified gold electrode (β-CD-SH--GR/Au) was prepared by electrochemical reduction of thiol-β-cyclodextrin-graphene oxide (β-CD-SH--GO/Au). The composite of p-CD-SH/GO was directly synthesized on the surface of Au electrode by electrochemical polymerization using the chrono amperometry, and then reducted by cyclic voltammetry (CV). Meanwhile, the electrochemical behavior of nonylphenol (NP) was studied by CV and differential pulse voltammetry (DPV). It was found that the oxidation current on β-CD-SH--GR/Au electrode was much higher than on the Au, β-CD-SH/Au and β-CD-SH--GO/Au electrodes. The oxidation potential shifted negatively, indicating that the β-CD-SH--GR/Au electrode had obviously catalytic activity on the oxidation of NP. Under the optimized conditions, the oxidation peak current exhibited a good linear relationship in the concentration range from 0.07 to 70 µmol L-1 (R = 0.9952) and the detection limit was 0.061 µmol L-l (S/N = 3). The prepared electrode was successfully applied to the determination of NP with the recovery from 92.36% to 105.6%, showing a practical prospect in real samples. [ABSTRACT FROM AUTHOR]

The electrochemical oxidation of 1,4-dihydroxybenzene and 4-hydroxybenzyl alcohol (4 HBA) in aqueous solutions of different pH values has been studied. The deposition of polymer films on gold electrodes from solutions of 4 HBA was demonstrated by the rapid decrease in current observed in cyclic voltammograms (CVs) subsequent to the first scan. In contrast, no polymer films were formed at the electrode surfaces from solutions of 1,4-dihydroxybenzene regardless of the pH. The eigenvalues for the highest occupied molecular orbitals (HOMO) for both molecules, at all pH values studied, has been calculated and correlated, where possible, with oxidation potentials. [ABSTRACT FROM AUTHOR]

The proton transport property of Nafion nanothin films (4-300 nm) has been investigated by electrochemical impedance spectroscopy (FIS) using interdigitated array (IDA) of gold electrodes on SiO2 substrate. The proton conductivity has been investigated as a function of film drying/heating protocol, relative humidity, temperature and film thickness. It is found that the film treatment protocol makes a difference in film transport property. Ultimately, the proton conductivity and capacitance of the Nafion nanothin film is thickness- dependent, where the former decreased and the latter increased exponentially with decreasing film thickness. Moreover, the activation energy increased exponentially with decreasing film thickness. The proton conductivity of the thin films of Nafion is significantly lower than that of the membrane counterpart regardless of the thickness, which is consistent with the high activation energy found in the thin films. These differences are likely related to the polymer confinement and morphological differences between the thin films and the freestanding membrane. [ABSTRACT FROM AUTHOR]