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Electrode fabrication in microfluidic devices is often avoided due to the smaller footprint of the platform, associated complexity in the process, and absence of a well-established method. In this article a glass microchip with chemically modified and vapor deposited gold internal electrode was fabricated and used for biomolecule immobilization and electrochemical applications. The silanol (-OH) on glass surface of the microdevice was modified with (3-mercaptopropyl)trimethoxysilane prior to gold deposition to achieve a strong attachment of the metal film using the gold-thiol binding. The practical utility of the microdevice with gold surface was demonstrated by performing quantitative enzyme linked immunosorbent assay (ELISA) of human interferon gamma (IFN-γ) antigen, yielding a limit of detection (LOD) of 0.15 pg/mL compared to 4 pg/mL in the microplate assay. Additionally, the functionality of the internal electrode was established by performing cyclic voltammetry (CV) and linear sweep voltammetry (LSV) of potassium ferricyanide (III) in potassium chloride (KCl) solution using the proposed gold patterned electrode in the microchip, offering limits of detection of 0.14 and 0.11 mM for CV and LSV respectively. Both the ELISA and electrochemical assays were validated by generating calibration curves and using a control sample for the electroanalytical sensing applications. The measurements yielded experimental results that agreed with control concentration with 7% relative standard deviation (RSD). The promising reproducibility of the electrode in fabrication with no/minimum failure rate and its outstanding performance in immunosensor applications as well as an electron exchange surface makes our technique of gold electrode fabrication in microchips a state of the art. [ABSTRACT FROM AUTHOR]

In this study, the effect of halide anions on the selectivity of the CO2 reduction reaction to CO was investigated in choline‐based ethylene glycol solutions containing different halides (ChCl : EG, ChBr : EG, ChI : EG). The CO2RR was studied using silver (Ag) and gold (Au) electrodes in a compact H‐cell. Our findings reveal that chloride effectively suppresses the hydrogen evolution reaction and enhances the selectivity of carbon monoxide production on both Ag and Au electrodes, with relatively high selectivity values of 84 % and 62 %, respectively. Additionally, the effect of varying ethylene glycol content in the choline chloride‐containing electrolyte (ChCl : EG 1 : X, X=2, 3, 4) was investigated to improve the current density during CO2RR on the Ag electrode. We observed that a mole ratio of 1 : 4 exhibited the highest current density with a comparable faradaic efficiency toward CO. Notably, an evident surface reconstruction process took place on the Ag surface in the presence of Cl− ions, whereas on Au, this phenomenon was less pronounced. Overall, this study provides new insights into anion‐induced surface restructuring of Ag and Au electrodes during CO2RR, and its consequences on the reduction performance on such surfaces in non‐aqueous electrolytes. [ABSTRACT FROM AUTHOR]

In this work, the diamine oxidase (DAO) produced from pea seedlings was partially purified using ammonium sulphate precipitation, dialysis, and gel filtration chromatography. Partially purified DAO was immobilized covalently with the help of a cross-linker glutaraldehyde onto the chitosan- modified gold electrode. The properties of immobilized enzyme were evaluated by optimum pH, optimum temperature, activity recovery, and recyclability using putrescine dihydrochloride as substrate. After immobilization of DAO, optimum pH ranges from 6.0 to 7.0 did not change and optimum temperature of enzyme changed from 34 to 38°C in comparison to free DAO. The immobilized DAO preserved 81% activity of free DAO and permitted increased stability and reusability of the enzyme than its native form. After 15 cycles of usage, the immobilized DAO maintained around 51% of its original activity, and this activity prolonged for 30 days at 4°C. [ABSTRACT FROM AUTHOR]

This paper was aimed to modify gold electrode surface with a BODIPY derivative and to examine its electrochemical behavior on the modified surface. Firstly, a BODIPY derivative including azido terminal was synthesized and characterized with several techniques such as NMR, FT-IR, element analysis and melting point. For the electrochemical studies, a triple electrode system was applied, with Gold electrode, Ag/AgCl (in aqueous medium) or Ag/Ag+ (in non-aqueous medium) and a Pt wire. The modified surface has been characterized using different electrochemical techniques. Then, the morphologies of the bare and modified electrode surfaces were evaluated with Scanning Electron Microscopy and Atomic Force Microscope. The metal adsorption property of the modified surface was investigated by using a copper solution. [ABSTRACT FROM AUTHOR]

The electrochemical oxidation of bio‐based 5‐hydroxymethylfurfural (HMF) results in 2,5‐furandicarboxylic acid (FDCA), which is a renewable and environmentally friendly alternative to terephthalic acid. Using a gold electrode, we compare the electrochemical oxidation of the aldehyde and alcohol functionality in HMF to the isolated functionalities represented by ethanol and acetaldehyde. Thereby, we investigate the effect of the inert furan ring on the electrochemical reaction. The linear sweep voltammogram (LSV) of HMF in a weakly adsorbing electrolyte differs only marginally from the superposition of LSVs obtained in ethanol and acetaldehyde containing electrolytes. However, in the presence of strong adsorbates, only the kinetics of ethanol and acetaldehyde oxidation but not of HMF oxidation are hampered. We assign this to a stronger adsorption of HMF through the furan ring than through the alcohol and carbonyl functionality of ethanol and acetaldehyde. Hence, HMF is better equipped to compete for adsorption sites than aliphatic compounds. [ABSTRACT FROM AUTHOR]

Redox-active polymers have garnered significant attention as promising materials for redox capacitors, which are energy-storage devices that rely on reversible redox reactions to store and deliver electrical energy. Our focus was on optimizing the electrochemical performance in the design and synthesis of redox-active polymer electrodes. In this study, a redox-active polymer was prepared through step-by-step synthesis on a gold electrode. To achieve this, we designed an automatic sequential polymerization equipment that minimizes human intervention and enables a stepwise polymerization reaction. The electrochemical properties of the polymer gold electrodes were investigated. The degree of polymerization of the polymer grown on the gold electrode can be controlled by adjusting the cycle of the sequential operation. As the number of cycles increases, the amount of accumulated charge increases proportionally, indicating the potential for enhanced electrochemical performance. [ABSTRACT FROM AUTHOR]

Epirubicin is prescribed as an essential drug for treating breast, prostate, uterine, and gastrointestinal cancers. It has many side effects, such as heart failure, mouth inflammation, abdominal pain, fever, and shortness of breath. Its measurement is necessary by straightforward and cheap methods. The application of aptamer-based electrochemical sensors is accounted as a selective option for measuring different compounds. In this work, a thiol-modified aptamer was self-assembled on the surface of the gold electrode (AuE) boosted with carbon nano-onions (CNOs), and coupled with methylene blue (MB) as an electroactive tracker to achieve a sensitive and selective aptasensor. In the absence of the epirubicin, CNOs binds to the aptamer through a π-π interaction enhancing the MB electrochemical signal. When epirubicin binds to the aptamer, the adsorption of CNOs and MB to the aptamer is not well established, so the electrochemical signal is reduced, consequently, the epirubicin value can be measured. The prepared aptasensor demonstrated an excellent sensitivity with a curve slope of 0.36 μI/nM, and 3 nM limit of detection in the linear concentration range of 1–75 nM. The prepared aptasensor was accurately capable of measuring epirubicin in blood serum samples. [ABSTRACT FROM AUTHOR]

A CA19-9 electrochemical immunosensor was constructed using a hybrid self-assembled membrane modified with a gold electrode and applied to detect real samples. Hybrid self-assembled membranes were selected for electrode modification and used to detect antigens. First, the pretreated working electrodes were placed in a 3-mercaptopropionic acid (MPA)/β-mercaptoethanol (ME) mixture for 24 h for self-assembly. The electrodes were then placed in an EDC/NHS mixture for 1 h. Layer modification was performed by stepwise dropwise addition of CA19-9 antibody, BSA, and antigen. Differential pulse voltammetry was used to characterize this immunosensor preparation process. The assembled electrochemical immunosensor enables linear detection in the concentration range of 0.05–500 U/mL of CA19-9, and the detection limit was calculated as 0.01 U/mL. The results of the specificity measurement test showed that the signal change of the interfering substance was much lower than the response value of the detected antigen, indicating that the sensor has good specificity and strong anti-interference ability. The repeatability test results showed that the relative standard deviations were less than 5%, showing good accuracy and precision. The CA19-9 electrochemical immunosensor was used for the actual sample detection, and the experimental results of the standard serum addition method showed that the RSD values of the test concentrations were all less than 10%. The recoveries were 102.4–115.0%, indicating that the assay has high precision, good accuracy, and high potential application value. [ABSTRACT FROM AUTHOR]

A gold nanoparticles transparent electrode was realized by chemical reduction. This work aims to compare the transparent gold nanoparticles electrode with a more commonly utilized gold-film-coated electrode in order to investigate its potential use as counter-electrode (CE) in dye-sensitized solar cells (DSSCs). A series of DSSC devices, utilizing I−/I3− and Co(III)/(II) polypyridine redox mediators [Co(dtb)3]3+/2+; dtb = 4,4′ditert-butyl-2,2′-bipyridine)], were evaluated. The investigation focused firstly on the structural characterization of the deposited gold layers and then on the electrochemical study. The novelty of the work is the realization of a gold nanoparticles CE that reached 80% of average visible transmittance. We finally examined the performance of the transparent gold nanoparticles CE in DSSC devices. A maximum power conversion efficiency (PCE) of 4.56% was obtained with a commercial I−/I3−-based electrolyte, while a maximum 3.1% of PCE was obtained with the homemade Co-based electrolyte. [ABSTRACT FROM AUTHOR]

• Sulfur-functionalized graphene (S-Graph) were prepared through non-thermal plasma process. • S-Graph is a novel hydrophilic graphene-based material with sulfur entities at the edge sheets. • Novel electrochemical method for simultaneous detection of TBHQ and BPA was developed. • The high affinity of gold electrode and S-Graph (strong Au−S covalent bound) made the sensor very stable. • Low-cost strategy for the quantification of BPA and TBHQ simultaneously. Electrochemical sensors based on graphene have proven to be powerful tools for detecting bisphenol A (BPA) and tert-butylhydroquinone (TBHQ) individually. There are currently no reports of these analytes being detected simultaneously. By assembling graphene-based materials on gold surfaces, it is possible to improve the charge transfer of both analytes. This study utilized non-thermal plasma-assisted synthesis with a sulfur-containing precursor to functionalize graphene (S-Graph), resulting in the fabrication of an ultrasensitive electrochemical sensor that can detect both BPA and TBHQ, simultaneously. Compared with native graphene or a traditional surface of gold electrode, S-Graph/Au retained superior electrochemical activity for both analytes that showed significantly enhanced sensing performance, including a wide linear range, with a detection limit of 13 and 54 nmol L−1 for TBHQ and BPA, respectively. The enhanced long-term storage stability, as well as reproducibility showed that S-Graph is a promising strategy for promoting the application of novel graphene-based materials. [Display omitted] [ABSTRACT FROM AUTHOR]

[Display omitted] • First comparative report on the electrochemical behavior of NAR using unmodified electrodes. • Selective and sustainable electroanalytical method for detecting NAR. • Linear range of 1.36 to 19.1 mg L-1 (LOD 0.11 mg L-1) for GCE. • Electronic structure of NAR probed using B3LYP/Def2-TZVPPD calculations alongside Fukui and dual descriptor analyses. • Cost-effective strategy for electroanalysis of pharmaceutical formulations. Naringenin (NAR) is a versatile herbal flavonoid known for its broad pharmacological benefits, including antioxidant, anti-inflammatory, and anticancer properties. These properties underscore its potential and necessity for industrial applications within the pharmaceutical sector, making its detection and quantification crucial for ensuring the quality and efficacy of pharmaceutical products. Addressing the imperative for a sensitive and sustainable screening approach, this research leverages electrochemical analysis techniques including electrochemical impedance spectroscopy (EIS), cyclic voltammetry (CV), and differential pulse voltammetry (DPV). Complementary to experimental investigations, the electronic structure of NAR was probed using B3LYP/Def2-TZVPPD calculations alongside Fukui and dual descriptor analyses. Our findings delineate the dissociation kinetics of the hydroxyl groups within NAR, with particular emphasis on the phenolic group's proton as the primary dissociation site, elucidating pivotal insights into the oxidation mechanism of NAR. Noteworthy is the irreversibility of the electrochemical oxidation process observed on both non-modified glassy carbon electrode (GCE) and gold electrode (GE), indicating a one-electron-one-proton mechanism. Utilizing the external calibration method and GCE, a linear range from 1.36 to 19.1 mg L-1 in Britton-Robinson (BR) supporting electrolyte was established, exhibiting a limit of detection (LOD) of 0.11 mg L-1 (R2 = 0.9945). For GE, the standard addition calibration approach revealed one linear range, from 0.27 to 0.48 mg L-1 (LOD of 0.04 mg L-1, R2 = 0.9960). Importantly, the proposed methodologies demonstrate satisfactory selectivity against potential interferences, with intra- and inter-day precision exhibiting low relative standard deviation (RSD) values. This study introduces a simple, sensitive, stable, selective, and sustainable electroanalytical method for the detection of NAR in pharmaceutical formulations, harnessing the advantages of unmodified electrodes and rigorous experimental validation. [ABSTRACT FROM AUTHOR]

Herein, a series of Co III corroles with different meso -substituents were successfully functionalized on gold electrodes through self-assembled axial coordination with 4-(methylthio)pyridine (MTP) and 4-(4-methylthiobenzo)pyridine (MTPP). The surface modified gold electrode performed enhanced and tunable electrochemically catalyzed hydrogen evolution behaviors that demonstrates the tunable surface molecular engineering of CoIIIcorroles via self-assembled monolayer is an effective strategy for energy related small molecule activations. Additionally, the CoIIIcorrole with electron-withdrawing meso -substituents axially coordinated with expanded conjugation system, 4-(4-methylthiobenzo)pyridine (MTPP), has the best performance of electrochemically catalyzed hydrogen evolutions. • CoIIIcorroles were successfully functionalized on gold electrodes through axially coordinated with pyridine ligands. • 4-(Methylthio)pyridine (MTP) and 4-(4-methylthiobenzo)pyridine (MTPP) with different conjugated system were tested. • The surface modified gold electrode performed enhanced and tunable electrocatalyzed hydrogen evolution behaviors. • The tunable surface molecular engineering of CoIIIcorroles via self-assembled monolayer is an effective strategy for HERs. • The CoIIIcorrole with EWG-substituents axially coordinated with expanded MTPP has the best performance of HERs. [ABSTRACT FROM AUTHOR]

Hydrogen evolution reaction (HER) on Au electrode in perchloric acid and NaOH solutions were studied using an inverted rotating disc electrode (IRDE). IRDE enables investigations of gas evolution reactions in a large potential and current window. In this configuration, the electrode is not obstructed by the product gas bubbles. Potentiodynamic polarization data were acquired at various concentrations of HClO 4 and NaOH, and at a few electrode rotational speeds. At large over-potentials, diffusion-limited currents were observed in HClO 4 solutions. In the case of HER on Au in acidic media, the Volmer-Heyrovsky-Tafel (VHT) mechanism best describes the polarization results. The fractional surface area covered by adsorbed hydrogen and the rate of reaction for individual steps were estimated using the model. At low H+ concentrations, HER proceeds mainly by the Volmer-Tafel (VT) pathway while at high H+ concentrations, Heyrovsky and Tafel pathways are equally important. In the alkaline media, HER rate was found to be independent of NaOH concentration and electrode rotational speed, and the reaction mechanism could not be identified unambiguously. The results illustrate the importance of analyzing data acquired at several reactant concentrations and at a wide potential range, to identify the reaction mechanism. [Display omitted] • Inverted rotating disc electrode to study HER in large potential/current window. • HER in HClO 4 solutions limited by mass transfer of H+ ions. • At low acid concentrations, on Au, Volmer-Tafel is the main HER route. • At high acid concentration, on Au, Heyrovsky step also contributes. • HER in alkaline media independent of NaOH concentration and rotational speed. [ABSTRACT FROM AUTHOR]

This work focused on the development and optimization of an impedimetric label-free immunosensor for detecting deoxynivalenol (DON). A monoclonal antibody for DON detection was immobilized on a modified gold electrode with a cysteamine layer and polyamidoamine (PAMAM) dendrimers. Cyclic voltammetry and electrochemical impedance spectroscopy techniques were used to monitor the layer-by-layer development of the immunosensor design, while electrochemical impedance spectroscopy and differential pulse voltammetry were employed to investigate the antigen/antibody interaction. The PAMAM dendrimers, allowing to immobilize a large number of monoclonal antibodies, permitted reaching, through the DPV technique, a high sensitivity and a low limit of detection equal to 1 ppb. The evaluation of the possible reuse of the immunosensors highlighted a decrease in the analytical performances of the regenerated immunosensors. After evaluating the matrix effect, the developed immunosensor was used to quantify DON in pasta samples spiked with a known mycotoxin concentration. Taking into consideration the DON extraction procedure used for the pasta samples and the matrix effect related to the sample, the proposed immunosensor showed a limit of detection of 50 ppb, which is lower than the maximum residual limit imposed by European Regulation for DON in dry pasta (750 ppb). [ABSTRACT FROM AUTHOR]

[Display omitted] • Bicarbonate reduction is an important pathway for hydrogen evolution on gold and platinum electrodes. • The rate of bicarbonate reduction is strongly dependent on mass transport. • The rate of bicarbonate reduction is strongly dependent on cations, in different ways for platinum and gold. • Bicarbonate reduction is most likely a direct reduction pathway, not mediated by solution acid-base reaction. Buffers are often employed as electrolytes for their ability to resist to pH changes. Still, they are not just spectators in the electrocatalytic processes, rather they may take a primary role. Here, we attempt to understand the mechanism of the hydrogen evolution reaction (HER) in bicarbonate-containing electrolytes on two distinct materials, Au and Pt. Keeping the bulk pH constant, voltammetric measurements reveal a promotional effect on the HER rate in the presence of bicarbonate buffer, as well as a substantial change in the reaction mechanism with a Tafel Slope in bicarbonate resembling the one in acidic media (ca. 100 and 40 mVdec−1 on Au and Pt, respectively). Nevertheless, because of the increase in surface pH due to the concomitant water reduction (2H 2 O + 2e− → H 2 + 2 OH−), bicarbonate is consumed by acid-base reactions and the bicarbonate branch of HER becomes significant only in the presence of large bulk buffer concentrations. Bicarbonate and water reduction appear intrinsically different, as they exhibit opposite dependence on the cation identity and scale differently with the specific area of the electrode. Through microkinetic modelling, we exclude that HER in bicarbonate can be explained via the generation of a proton by solution acid-base reactions. Rather, we suggest a direct bicarbonate reduction pathway, which, due to the negatively charged reactant, is strongly dependent on the cation concentration. [ABSTRACT FROM AUTHOR]

Monolayer Co(II)phthalocyanine (Co(II)Pc) functionalized gold electrodes through self-assembled axial coordination with 4-(methylthio)pyridine (MTP) and 4-(4-methylthiobenzo)pyridine (MTPP) were prepared. The surface modified gold electrode performed electrochemically catalyzed oxygen reduction in terms of onset-potential, current density, overpotential and Tafel in the order Au < Au/Co(II)Pc < Au/MTP/CoPc(II) < Au/MTPP/Co(II)Pc that demonstrates tunable surface molecular engineering of Co(II)Pc via self-assembled monolayer is an effective strategy for molecular catalysis and device application. [ABSTRACT FROM AUTHOR]

We studied the electrochemical reduction based on gold electrode of a diazonium salt prepared from ethylenediamine. This is the first time where the covalent functionalization on the gold electrode of an alkyldiazonium salt, 2-aminoethane-1-diazonium chloride, is demonstrated. This step requires the preparation beforehand by diazotization of one amine group from ethylenediamine. The resulting electrodeposited ethylamine film was confirmed by spectroscopic characterizations from gold surface modification monitored by electrochemical quartz crystal microbalance (EQCM) coupled to cyclic voltammetry (CV). The development of chemosensors based on such a covalent functionalization of a metal can reduce the chemical threats to human health along with drastically removing contaminants according to the green chemistry principles. [ABSTRACT FROM AUTHOR]

Hexavalent chromium is one of the toxic heavy metals found in wastewaters from industries like electroplating, leather tanning, and steel manufacturing. The Cr(VI) removal and quantitative detection are among the major concerns from an environmental toxicity point of view. In the present work, we report an effective electrochemical technique for Cr(VI) monitoring based on the utilization of gold electrode. The technique developed is user-friendly, non-destructive, and provides real-time monitoring of Cr(VI) from wastewaters in contrast to other spectroscopic and optical techniques. The technique developed was applied in monitoring Cr(VI) removal from synthetic Cr(VI) samples using chitosan cross-linked glutaraldehyde (C + G) beads. The parameter optimization for Cr(VI) removal using C + G beads was done. The experimental data of Cr(VI) adsorption on C + G beads obtained using cyclic voltammetry were further used for kinetic and thermodynamic studies. Kinetic and thermodynamic studies found that Cr(VI) adsorption follows pseudo-second-order kinetics and Modified Langmuir isotherm. The maximum adsorption capacity of C + G beads for Cr(VI) was found to be 28.65 mg g−1. These results obtained indicate that the cyclic voltammetric technique using gold electrode can be effectively applied for Cr(VI) analysis from wastewaters. [ABSTRACT FROM AUTHOR]

Perovskite solar cells (PSCs), a promising third-generation photovoltaic technology, have drawn considerable attention. Yet, their conventional metal back electrode layer, often composed of gold or silver, presents environmental and stability challenges. In this study, we conducted a lab-scale optimization of perovskite solar cells utilizing gold and carbon electrodes. A cradle-to-gate life cycle assessment (LCA) was performed using primary data from Thailand's National Nanotechnology Center (NANOTEC) and the Sima Pro 9.3.0.2 software with the ReCiPe 2016 impact methodology, consisting of 18 midpoint and three endpoint impact categories. Our analysis reveals that transitioning from gold electrodes (PSC-Au) to carbon electrodes (PSC-CB) fabricated through a low-temperature process not only maintains equivalent power conversion efficiency but also enhances stability, resulting in significantly reduced environmental impacts across all categories, with an impressive 86% reduction in global warming potential (GWP) per 1 kWh of energy produced. Furthermore, sensitivity analysis underscores PSC-CB's superiority in GWP compared to other established renewable energy technologies, provided its operational lifespan extends to 15 years. These findings highlight PSC-CB's substantial potential for commercialization as a sustainable renewable energy technology. • Cradle-to-Gate LCA for the same architecture and performance of PSCs between the Gold electrode and Carbon electrode • Thermal evaporation and gold material loss in the process were indicated as hotspot and commercialization barriers • Carbon electrodes cut environmental impact by over 79% or an average of 93.9% across all categories versus gold electrodes • PSCs with carbon electrodes surpass other renewables in global warming impact when a device lifespan exceeding 15 years [ABSTRACT FROM AUTHOR]

In this study, a molecularly imprinted electrochemical sensor (MIP/DA) was investigated for selective and sensitive determination of dopamine (DA) by electrochemical polymerization of p‐aminothiophenol in the presence of DA on gold electrode. According to electrochemical behaviour of the sensor, gained through cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS), MIP/DA sensor showed distinctive electron transfer characteristics in comparison to the non‐imprinted (NIP/DA) sensor. Besides the MIP/DA sensor showed high selectivity for dopamine through its analyte specific cavities. The sensor had a broad working range of 5.0×10−8–2.0×10−7 M with a limit of detection (LOD) of 1.8×10−8 M and the developed sensor was successfully applied for determination of dopamine in pharmaceutical samples. [ABSTRACT FROM AUTHOR]

A voltammetric technique for electrochemical sensing and quantification of granulocytosis risk inducing metabolite of aminopyrine, 4-Aminoantipyrine (4-AAP) at gold electrode has been developed. The gold electrode shows excellent selectivity and sensitivity towards the oxidation of 4-AAP in phosphate buffer solution (PBS) of pH=3.0. It is observed from the electrochemical studies of scan rate that overall electrode process is diffusion controlled and pH effect suggests involvement of protons in electrochemical oxidation of 4-AAP. A linear current response towards the electrochemical oxidation of 4-AAP in the concentration range of 1.0 × 10-6 - 2.5 × 10-5 M is observed with limit of detection of 3.8 × 10-8 M (S/N = 3). The interference studies have shown that the gold electrode exhibited excellent selectivity in presence of large excess of interferents. The method is employed to recovery study of 4-AAP in spiked urine and serum samples. [ABSTRACT FROM AUTHOR]

Cement and clinker are complex samples and constitute a challenge for elemental analysis. Manganese, usually present in these matrices, can accumulate in bones, liver, the pancreas, kidneys, and brain and its monitoring is very important. This work presents an alternative method of sample treatment based on ultrasonic-assisted extraction for the determination of trace amounts of manganese in cement and clinker samples by square wave cathodic stripping voltammetry (SWCSV) on a gold working electrodes. The proposed extraction procedure occurs at room temperature inside closed vessels and uses 3.0 mol L−1 HCl solution, a less corrosive extractant compared to concentrated acids. Ultrasonic extraction was compared with conventional extraction by heating on hot plate and no significant differences between the two extraction methods were observed at the 95% confidence level. The possible use of H2O2 in the extraction process was evaluated but not used due to its interferences in the electrochemical determination of manganese. The SWCSV results obtained employing 0.20 mol L−1 H3BO3/0.10 mol L−1 KCl electrolyte at pH 6.5 produced two distinct linear regions of concentration for the analytical curve from 1.1 to 2.0 × 10−7 mol L−1 and from 2.0 to 3.2 × 10−7 mol L−1. The limits of detection and quantification were 3.1 × 10−8 mol L−1 and 9.8 × 10−8 mol L−1, respectively, and suitable for the proposed application. The results obtained by SWCSV were consistent with those obtained by flame atomic absorption spectrometry (FAAS) at the 95% confidence level. [ABSTRACT FROM AUTHOR]

Voltammetric detection of the K-ras gene fragment was accomplished through the combined application of (a) a switchable DNA nanostructure, (b) the use of hairpin probe and exonuclease III (Exo III)-assisted signal amplification, (c) a split G-quadruplex, and (d) by exploiting the redox activity of DNAzyme. Three assistant oligonucleotides were designed to construct a DNA tweezer on a gold electrode. It is in "open state" in the absence of K-ras DNA. Then, a hairpin probe was introduced, whose stem-loop structure can be opened through hybridization with the K-ras DNA. Exo III is added which hydrolyzes the complementary region of the hairpin sequence to release a single-stranded rest fragment. The ssDNA hybridizes with the DNA tweezer on the electrode which thereby is switched to the "closed state". This leads to the formation of G-quadruplex due to the shortened distance of the split G-quadruplex-forming sequences in the tweezer. The voltammetric signal of the G-quadruplex-hemin complex, with a peak near −0.3 V vs. Ag/AgCl, is used as the signal output. Under the optimal conditions, the current response in differential pulse voltammetry (DPV) increases linearly with the concentration of K-ras DNA in the range of 0.01–1000 pM, and the detection limit is 2.4 fM. The assay can clearly discriminate K-ras DNA from a single-base mutation. The method has excellent selectivity and was applied to the determination of K-ras DNA in (spiked) serum samples. [ABSTRACT FROM AUTHOR]

Catalytic oxidation of water by manganese complexes is of great interest because it can serve as a model for the natural oxygen evolving complex, Mn4CaO5. Complex compounds are highly active and tunable, but their limited stability and solubility restrict them for practical water oxidation applications. In the present article we have prepared surface anchored Mn(II)‐complexes, [MnII(H2O)2(X)2(dcbpy)] (where dcbpy= 4,4′‐dicarboxy‐2,2′‐bipyridine; X=acetate, sulphate, chloride ions) on gold electrode surface using self‐assembly process and applied for the electrocatalytic oxidation of water in neutral pH. The modified electrode was characterized by using different spectral, microscopic and electrochemical techniques. The Mn(II)‐acetate containing gold electrode (Mn(II)‐dcbpy‐Au) electrocatalytically oxidized water at a current density of 1.6 mA cm−2 with low overpotential ∼ 310 mV and a Tafel slope of 56 mV/decade. The modified electrode showed high electrochemical stability during controlled potential electrolysis. It was also observed that the Mn(II)‐acetate immobilized on dcbpy‐Au electrode showed higher electrocatalytic activity in oxidation of water than Mn(II)‐chloride or Mn(II)‐sulfate containing dcbpy‐Au electrode. The newly in‐situ generated Mn(II)‐complex modified electrode is inexpensive and highly efficient for the catalytic oxidation of water than the surface bound Mn‐based electrocatalysts reported previously. [ABSTRACT FROM AUTHOR]

The oxidation of sulfite at a renewable gold electrode in solutions with pH values ranging from 2 to 14 was studied using voltammetry. The voltammogram obtained for sulfite oxidation did not change when the solution pH was varied from 2 to 11, indicating that the process rate is independent of the acidity and partial composition of the solution. This result is in agreement with the overall reaction for the dimerization of sulfite ions, which leads to the formation of dithionate: 2 SO 3 2 − → S 2 O 6 2 − + 2 e − . Within the pH range 11–14, an increase in pH was accompanied by a shift in the sulfite oxidation potential and a decrease in the current. This result is concordant with the O-transfer reaction, which leads to the formation of sulfate: SO 3 2 − + 2 OH − → SO 4 2 − + H 2 O + 2 e − . The mechanism of sulfite oxidation changes across the pH range 11–12.5; the reaction occurs in a narrow potential range (0.6–0.8 V) in this pH interval and is accompanied by anomalously sharp changes in the measured current. [ABSTRACT FROM AUTHOR]

The effects of three different substrate materials (glassy carbon, gold, and nickel electrodes) on the electrocrystallization behavior of nanocrystalline nickel in an industrial electrolyte with complex compositions were studied by cyclic voltammetry (CV), single potential step chronoamperometry. The CV results indicated that the initial deposition potentials of nickel shift to the positive direction in the order glassy carbon < gold < nickel electrodes, while the nickel deposition overpotential decreased at the same time. Chronoamperometry results indicated that from the glassy carbon to gold and nickel electrodes, the adhesion of nickel nanoparticles on the electrodes increased, nucleation relaxation time became shorter, and the number of nuclei decreased. As the deposition potential is negatively shifted and the deposition time is prolonged, the I-t curves for the nickel and gold electrodes are more stable and reliable than those from the glassy carbon electrodes. The chronoamperometric study combined with SEM revealed that the nucleation mechanism of nickel on different substrates changed from three-dimensional progressive to instantaneous, but the time of the transition is different. When the deposition time is 100 s, the nanocrystalline nickel deposited on the nickel and gold electrodes has good integrity and uniformity. This was also confirmed in studies using atomic force microscopy and transmission electron microscopy. Moreover, the results of transmission electron microscopy (TEM) show that there are many twins in the nanocrystalline nickel layer deposited on the gold electrode at −0.95 V, 100 s. The electrocrystallization process of nickel is complicated by the complex ionic components in the industrial electrolyte of the nickel sulfide soluble anode/mixed acid system. • Different substrates do not change the electrocrystallization mechanism of nickel. • Glassy carbon electrode is not suitable for prolonged high-potential nickel deposition. • Electrocrystallization of nickel is complicated by the complex electrolyte composition. [ABSTRACT FROM AUTHOR]

An efficient and new electrochemical biosensor for detection of DNA damage, induced by the interaction of the hybrid anti-cancer compound (7ESTAC01) with DNA, was studied by differential pulse voltammetry (DPV). The biosensor consists of a Stem-Loop DNA (SL-DNA) probe covalently attached to the gold electrode (GE) surface that hybridizes to a complementary DNA strand (cDNA) to form a double-stranded DNA (dsDNA). The interaction and DNA damage induced by 7ESTAC01 was electrochemically studied based on the oxidation signals of the electroactive nucleic acids on the surface of the GE by DPV. As a result, the SL-DNA/GE and dsDNA/GE were tested with the reduced 7ESTAC01, showing the voltammetric signal of guanine and adenine, increase in the presence of 7ESTAC01. Under optimum conditions, the dsDNA/GE biosensor exhibited excellent DPV response in the presence of 7ESTAC01. The bonding interaction between 7ESTAC01 and calf thymus DNA (ctDNA) was confirmed by UV–Vis absorption spectroscopy, dynamic simulations (performed to investigate the DNA structure under physiological conditions), and molecular docking. Theoretical results showed the presence of hydrogen bonding and intercalation in the minor groove of DNA, involving hydrophobic interactions. • A sensitive electrochemical Stem-Loop DNA biosensor is proposed to detect DNA-hybrid cancer drug intercalation. • A novel hybrid anti-cancer drug, acridine and thiophene, intercalate into the DNA as a dominant mode. • This biosensor can be applied as DNA oxidative damage evaluation method for other cancer drugs candidates. [ABSTRACT FROM AUTHOR]

Abstract The interactions of cationic lipopeptide C 15 H 31 CO-Trp-Lys-D-Leu-Lys with model lipid bilayers supported on gold surface were investigated using electrochemical methods combined with atomic force microscopy imaging and quartz crystal microbalance measurements. It has been found that the mode of the lipopeptide action strongly depends on the net charge of the lipid membrane. In case of the negatively charged bilayers composed of l -α-phosphatidylethanolamines and l -α-phosphatidylglycerols extracted from E. coli bacteria, C 15 H 31 CO-Trp-Lys-D-Leu-Lys molecules initially aggregate on the top of the membrane as a result of the electrostatic attraction between cationic peptide moiety and anionic polar heads of phosphatidylglycerols. Further fusion of the aggregates leads to the swelling and partial disruption of the membrane, while its permeability is substantially increased. Interestingly, the changes in the molecular organization of negatively charged membrane were much more pronounced in the upper leaflet of the bilayer. The effect of C 15 H 31 CO-Trp-Lys-D-Leu-Lys on zwitterionic bilayer composed of 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine and cholesterol was definitely different. In this case, the disturbance of the membrane structure was rather subtle. It has been observed that a small fraction of lipopeptide molecules rapidly inserts into the bilayer and perturbation of the assembly is homogenous throughout the film. This was followed by a noticeable decrease in membrane permeability and stiffening of the lipid bilayer. Such sealing effect indicates that the insertion of lipopeptide did not result either in pore formation or membrane rupture. [ABSTRACT FROM AUTHOR]

Persulfate (PDS), peroxodisulfate, peroxydisulfate, peroxodisulfuric acid, is an oxidant that can be generated by direct oxidation of sulfate ions or indirectly via reaction with hydroxyl radicals in anodes with high oxygen overpotential. Quantitative methods for determining/quantifying PDS in the presence of other strong oxidants or other anions in eco-friendly applications do not give reliable results because of these interferents. Therefore, an additional method is needed to improve the efficacy to determine/quantify the PDS concentration in oxidative environments. In this frame, an alternative sensing approach was developed based on the electroreduction of PDS in the polycrystalline gold electrode using the square wave voltammetry (SWV) technique for its detection and quantification. Then, the procedure was evaluated in terms of its effectiveness for determining PDS in complex matrices, such as in the electrolysis of sulfate ion precursor solutions using anodes with high oxygen overpotential (e.g.: diamond electrode) capable of generating other strong oxidants. Based on the results obtained, it was confirmed that only the direct electron transfer step is attained when PDS is electrochemically synthetized at the surface of the polycrystalline gold electrode, contributing to its detection and quantification by SWV. It was also observed that at acidic conditions, the PDS electroreduction process is controlled by mass transfer while that the sensitivity for PDS detection is improved, achieving detection limits of about 14 and 19 μM for perchloric and sulfuric acids medium, respectively. When the electrolysis of sulfate-based solution at acidic conditions was performed to determine the electrochemical production of PDS by SWV approach with Au sensor, the concentration of PDS was effectively determined and no interferences were assessed by other strong oxidants generated during the electrolysis. Conversely, the spectrophotometric method showed that, the results of the PDS concentration were overestimated and other strong oxidants significantly interfere with its determination during the electrolysis of sulfuric acid solutions. Therefore, the electroanalytical method presented here is a suitable alternative for determining PDS during the applicability of the environmental-electrochemical technologies. [Display omitted] • Persulfate detection and quantification by using gold electrode. • Electroanalytical approach is significantly reliable than spectrophotometric method. • Au sensor can be used to quantify persulfate during advanced electrooxidation processes. [ABSTRACT FROM AUTHOR]

In this paper, an electrochemical aptasensor based on gold electrode (AuE)-modified Ag@Au core-shell nanoparticles was prepared. The surface of AuE was modified with Ag@Au core-shell nanoparticles to elevate APT binding sites and accelerate electron transfer properties between the electrode and ferrocene (Fc). When SM2 existed, the aptamer conformation would change and the response current intensity would increase because the Fc was pulled closer to the electrode surface. Subsequently, through a series of conditional optimization analysis, the optimal values of volume of Ag@Au core-shell, APT concentration, APT incubation time, and SM2 incubation time were 9 μL, 0.2 μmol/L, 75 min, and 40 min, respectively. Under optimum conditions, the results of differential pulse voltammetry experiments showed that the linear relationship was good in the range of 0.1~50 ng/mL, ΔI′ (μA) = 1.145C (ng/mL) + 54.666, R2 = 0.964, with a detection limit of 0.033 ng/mL. The spiked recovery for SM2 in the pork samples was 92.6~101.0% and the relative standard deviation (RSD) was 2.7~4.1%, which indicated that the proposed aptasensor exhibited desirable performance in actual sample analysis.An electrochemical aptasensor based on gold electrode-modified Ag@Au core-shell nanoparticles was prepared. The detection principle was on the basis of the change of current signal of DPV in Tris-HCl buffer solution before and after incubation of SM2. After the formation of APT-SM2 complex, the ferrocene modified on the aptamer was pulled closer to the electrode surface and sped up the electron transfer rate. [ABSTRACT FROM AUTHOR]

The electrochemical behavior of polycrystalline gold electrode (PAuE) modified by self-assembled monolayers (SAMs) of thiolated calix[4]arene (C4A) and undecanethiol (C11) was investigated by voltammetric methods and electrochemical impedance spectroscopy. Coverage of the thiol SAMs and their stability was tested. The C11 layer is very stable; the desorption peak was recorded only in basic solutions of pH 12 and higher (at −1.30 V vs. Ag|AgCl (3 mol L −1 KCl)). The position of the C4A desorption peak is more pH dependent and it was recorded at −1.08 V at pH 13. Molecular coverage for C4A and C11 SAMs modified PAuE is 364 ± 52.9 μC cm −2 and 137 ± 20.0 μC cm −2 respectively. The properties of the PAuE modified by C11 and/or C4A were investigated using the model compounds hydroquinone, ferrocene and potassium ferrocyanide. It is assumed that the oxidation of the hydroquinone cannot be realized inside the C4A cavity because the hydroquinone molecule is too big to enter the cavity. Similar behavior was observed using potassium ferrocyanide. In contrast, cyclic voltammograms of ferrocene oxidation were only negligibly affected by the electrode modification. Moreover, capacitance measurements proved accumulation of ferrocenium ions at the C4A modified electrode. [ABSTRACT FROM AUTHOR]

In the present work a fast, reliable and safe Ion Exchange Chromatography-Pulsed Amperometry Detection (IC-PAD) method for direct determination of free cyanide in drinking water has been reported. To the best of our knowledge for the first time we are reporting the application of Gold working electrode for detection of free cyanide in a chromatography system. The system shows a wide linear range up to 8000 µg/L. The electrode was found to have improved sensitivity and selectivity in the presence of interfering ions. The detection limit of the system was calculated to be 2 µg/L. Long term evaluation of the electrode was found to be stable. Reproducible results were obtained from analysis of drinking water samples with recoveries of 98.3–101.2% and Relative Standard Deviations (RSD) of <2%. This study proves the potential application of the newly developed method for the analysis of free cyanide in drinking water. [ABSTRACT FROM AUTHOR]

An electrochemical sensor is described for the determination of microRNA-21 by combing the DNA generated current with targettriggered hybridization chain reaction (HCR). A thiol-modified hairpin capture probe was first immobilized on a gold electrode. In the presence of microRNA-21, hybridization leads to a conformational change of the capture probe. The conformational change triggers HCR to generate a long DNA strand on the surface of the electrode. The phosphate backbone of the long DNA strand then reacts with molybdate to form the redox redox probe molybdophosphate, and this generates an electrochemical current. The HCR triggered by microRNA increases the amount of phosphate groups due to the extension of the DNA length, and thus increases the response current. The electrode, best operated at a voltage of 0.20 V, was successfully applied to the analysis of microRNA-21 in (spiked) human serum samples. In our perception, it represents a promising tool for analyzing a variety of microRNA biomarkers. [ABSTRACT FROM AUTHOR]

para-Nitrophenol (p-NP) is a high priority environmental pollutant. For the sake of safety, sensitive detection of its presence in water resources and food is highly important. The present article describes the use of copper metal nanoparticles for selective and sensitive electrochemical detection of p-NP in pure and real sample. For this the gold electrode was fabricated by polyvenylpyrrolidone stabilized copper metal nanoparticles ( ca. 4 nm d.) via self-assembled 4,4′-bipyridine monolayer and characterized by microscopic and electrochemical techniques. The newly developed sensor permits for sensitive detection of p-NP in a linear concentration range of 1-500 μM with lowest detection limit of 0.34 nM and high sensitivities 247.1 μA cm−2 μM−1. The sensor electrode exhibited high stability, reproducibility, good selectivity in the presence of potential interfering agents and had an excellent capability for the selective determination of p-NP in river water without preliminary treatments. [ABSTRACT FROM AUTHOR]

A thiolated catechol (CA) consisting of 1,6-Hexanedithiol (HDT) and CA was modified on a gold (Au) electrode to obtain an amperometric L-cysteine sensor with detection limit of 60.6 nM. The preparation of thiolated CA was conducted via a thiol addition between HDT and electro-oxidized CA (EOCA). Briefly, the thiol addition reaction was accomplished by potential cycling of HDT/Au electrode in 0.1 M phosphate buffer (PB, pH 7.2) containing CA, and an EOCA-HDT/Au electrode was produced. The obtained EOCA-HDT/Au electrode exhibits a pair of well-defined redox peaks (at 0.22/0.10 V) of o-quinone moiety, which effectively mediates the oxidation of L-cysteine in a 0.1 M PB (pH 7.2), with an over-potential decrease by ca. 0.12 V (versus bare Au electrode). Electrochemical quartz crystal microbalance, cyclic voltammetry and surface-enhanced Raman spectra were used to study relevant processes and/or film properties. The amperometric L-cysteine sensor has good anti-interferent ability and reproducibility. It also has acceptable recovery for detection of L-cysteine in urine samples. [ABSTRACT FROM AUTHOR]

Photoactive material is a crucial factor which affects the sensitivity and selectivity of the photoelectrochemical (PEC) sensor. A simple PEC sensing platform was fabricated using nanoMoS 2 modified gold electrode (nanoMoS 2 /GE) in this paper. Three kinds of nanoMoS 2 , single-layer nanoMoS 2 , multiple-layers nanoMoS 2 and small-sized nanoMoS 2 , were used to modify the electrode. It was found that the single-layer nanoMoS 2 showed utmost PEC response. The photocurrent of nanoMoS 2 /GE was drastically improved upon the addition of dopamine, which was attributed to the life improvement of the electron-hole pairs. Based on the enhanced photocurrent signal, a PEC methodology for ultrasensitive determination of dopamine has been developed, which showed linearly enhanced photocurrent by increasing the dopamine concentration from 1.0 × 10 −11 M to 1.0 × 10 −5 M with a detection limit of 2.3 × 10 −12 M and the RSD was 3.9% at 2.0 × 10 −10 M (n = 9) under optimal conditions. This method showed high sensitivity, simplicity and wide linearity range which opened up a new promising signal-on PEC platform for small molecule detection in bioanalysis. [ABSTRACT FROM AUTHOR]

Detection and quantitation of interferon-gamma (IFN-γ) in blood is of vital importance for diagnosis of latent tuberculosis. The authors describe an electrochemical aptasensor for IFN-γ that is based on a triple-helix molecular switch (THMS). The combination of a THMS with amperometry makes the sensor selective, sensitive and fast (50 min). In the presence of IFN-γ, the structure of the THMS is disassembled and the electrochemical probes, Methylene Blue (MB), can only bind to the signal transduction probe (STP) on the surface of the gold electrode, this leading to a weak peak current. However, in the absence of IFN-γ, the structure of THMS is preserved and MB can interact with the THMS to result in strong current (typically measured at −0.24 V vs. silver reference electrode). Under optimized conditions, the assay has a 3 pg·mL detection limit and a linear range that extends from 10 to 1500 pg·mL. Employed to the determination of IFN-γ in spiked serum samples, it gave recoveries that ranged from 91.3% to 102.8%. [ABSTRACT FROM AUTHOR]

This paper presents a novel impedimetric sensor for the sensitive determination of ampyra (Am) based on the l -Cysteine/Cu (II) modified gold electrode (Cu (II)/L-Cys/AuE). This novel sensing layer was characterized by different techniques, including atomic force microscopy (AFM), cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS). Am determination by conventional electrochemical methods is not possible, because of its high redox overpotential. Therefore, [Fe(CN) 6 ] 3-/4- was used as a redox probe for the impedimetric determination of Am. Under the optimized conditions, the calibration curve for Am concentration was linear in the range 0.010–40.0 nM with a detection limit of 0.0028 nM. The practical applicability of the proposed sensor was examined by evaluating the detection of Am in biological fluids and pharmaceutical samples with satisfied recoveries. Therefore, the prepared sensor can hold great promise for fast, simple and sensitive detection of Am in various real samples. [ABSTRACT FROM AUTHOR]

The electrooxidation of glucose on a polycrystalline gold electrode from alkaline and saline solutions was investigated. The influence of Nafion on the oxidation of glucose under the same conditions was also studied. The presence of Nafion on the surface of a polycrystalline gold electrode decreased the rate of glucose oxidation in alkaline solution. The sensitivity of glucose determination was diminished. However, processes occurring at the electrode were clearly separated. Stable cyclic voltammogram of a polycrystalline gold electrode was obtained in saline solution. The addition of glucose to saline solution initiated the reaction of gold dissolution. The presence of Nafion on the electrode surface prevented the formation of hydrous gold oxide. The addition of glucose to saline solution led to the passivation of the Nafion-covered gold electrode. The gold electrode pretreated in alkaline solution and covered with Nafion was used for glucose detection in saline solution. The linear behavior was obtained in the concentration range from 2 to 10 mM with the slope of 0.0015 mA/mM and the coefficient of 0.95. The chronoampermetric response of the pretreated gold electrode covered with Nafion was also tested. [ABSTRACT FROM AUTHOR]

The authors describe an impedimetric method for the quantitation of the DNA of the human papilloma virus (HPV) type 16. A glassy carbon electrode (GCE) was modified with gold nanosheets and is shown to be superior to a common gold disk electrode. A single-stranded 25mer oligonucleotide (ssDNA) acting as the probe DNA was immobilized via its thiolated 5′ end on both electrodes. After hybridization with target (analyte) DNA, electrochemical impedance spectra were acquired in the presence of hexacyanoferrate as a redox marker. The sensor can distinguish between complementary, non-complementary and single base pair mismatches of HPV ssDNA. At a 1 mM hexacyanoferrate concentration, the biosensors respond to target DNA in the 1 μM to 1 pM concentration range, and the detection limit is 0.15 pM. The results illustrate that the use of gold nanosheets on a GCE distinctly improves the detection and differentiation of HPV compared to using bare gold. [ABSTRACT FROM AUTHOR]

The hydrogen reversible reaction (HRR) with ultra-low concentrations of platinum sites supported on a gold substrate is studied with decreasing amounts of active sites (estimate coverage range from 0.006 to 10 − 5 ) at a rotating electrode in a 0.5 M H 2 SO 4 solution. These particular experimental conditions allow the voltammetric study of the HRR without diffusion limitation in the whole range of potential. In the absence of a more precise determination of the amount of platinum surface sites, a method is given to compare results obtained from distinct experimental runs. Once eliminated the contribution of gold to the current recorded, it becomes possible to normalize the currents in the entire range of platinum coverage. It shows that below 0.2 V, the normalized HER and the HOR currents are linearly connected to the amount of active sites. At higher potentials the normalized currents indicate a systematic decrease of the efficiency of the active sites for HOR that deviates from linearity when their surface concentration decreases. Around the reversible potential, the voltammetric profiles obey to the Butler-Volmer formalism. The conditions of its applicability are discussed. The simulation of the experimental current allows the determination of the partial oxidation and reduction currents. The simulated reduction current is then compared to the HER current recorded in a solution without dissolved hydrogen and saturated with argon. The close fit of the two responses gives evidence for the possibility to have access to HER kinetic data free of diffusion. Finally a comparison is made between results obtained at ultra-low content of platinum active sites with pure platinum as well as for an intermediate coverage of gold with platinum. [ABSTRACT FROM AUTHOR]

The authors describe an electrochemical strategy for highly sensitive determination of ATP that involves (a) aptamer-based target recognition, (b) enzyme-free dendritic DNA nanoassembly amplification with multiplex binding of the biotin-strepavidin system, and (c) enzyme-amplified differential pulse voltammetric readout. In the presence of ATP, binding of ATP to the aptamer releases trigger DNA from the double-stranded complex between ATP aptamer and trigger DNA. The single-stranded thiolated capture probe, chemisorbed on the gold electrode surface, captures the released trigger DNA via hybridization. The toehold of the trigger DNA is recombined with one end of the first substrate DNA (1) which is on its other end biotinylated and blocked, with loops, by a counterstrand. The latter is removed by a complementary single-stranded helper (1) exposing two toeholds and two identical complimentary sequences for a second biotinylated substrate DNA (2). The latter, which is double-stranded except for the toehold, binds to one of these two sites. It is then stripped from its counter strand by another single-stranded helper DNA 2, exposing a toehold to bind another substrate DNA 1. On this substrate, another cycle with dentrimeric bransching can start. Substrate 1 with its two binding sites for substrate 2 initiates the assembly of dendritic DNA on the surface of the gold electrode, which finally possesses numerous biotins at the terminal ends of both of the associated substrate DNAs. Subsequent multiplex binding of streptavidinylated alkaline phosphatase and enzyme-amplified electrochemical readout leads to a highly sensitive electrochemical ATP aptasensor. If operated in the DPV mode, the current as measured at a typical working potential of 0.25 V (vs. Ag/AgCl) increases linearly over the 10 nM to 10 μM logarithmic ATP concentration range, and the detection limit is 5.8 nM (at an S/N ratio of 3). The assay is highly specific and reproducible. It was successfully applied to the detection of ATP in spiked human serum samples. [ABSTRACT FROM AUTHOR]

Although the adsorption of lipids on reconstructed Au(111) surface and formation of highly ordered stripe-like domains are well-known phenomena, the exact orientation of the molecules with respect to the substrate remains unclear. Therefore, in this study we have focused on the structure and arrangement of lipid molecules forming highly ordered stripe-like domains at gold electrode-electrolyte interface. N -palmitoyl-D- erythro -dihydroceramide-1-phosphate was selected as model compound since its ability to transform into hemimicellar structure is limited. This way it was possible to get very stable lipid film with characteristic stripe-like pattern. Application of complementary techniques such as atomic force microscopy and scanning tunneling microscopy enabled detailed characteristics of lipid adlayer adsorbed on Au(111) electrode. Based on careful analysis of the experimental results, we have proposed a model which describes the arrangement of the molecules within the film. In general, it assumes flat-lying orientation of the lipids but only one hydrocarbon chain of phosphorylated dihydroceramide is involved in direct interaction with gold. [ABSTRACT FROM AUTHOR]

In this research, electrochemical and spectroelectrochemical behaviors of acrylamide (AA) have been studied using cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS). Cyclic voltammetric studies of AA in acetonitrile (CH3CN) containing 100 mM tetrabutylammonium tetrafluoroborate (NBu4BF4) on glassy carbon (GC) electrode was performed between 0.0 mV and +2600 mV potential range, on platinum (Pt) electrode was performed between 0.0 mV and +1500 mV potential range and gold (Au) electrode was performed between +600 mV and +2200 mV potential range at 100 mVs-1 scan rate with 10 cycles. The surface characterization process was carried out using CV and EIS technique in both aqueous and non-aqueous media. [ABSTRACT FROM AUTHOR]

Gold film electrodes (Au-FE) with distinct nanostructured patterns were prepared from polycarbonate (PC) substrates and investigated with respect to their analytical sensitivity. The recordable (R) and read-only memory (ROM) discs, respectively, yield PC substrates with grooves (stripe pattern) or pits (indented pattern). The Au-FEs were characterized in terms of surface morphology and surface patterns, and it was found that the surface area of all Au-FEs does not significantly differ (by 0.2 to 7.4 %) compared to electrode with flat surfaces. However, the electrical signal of indented patterns is larger by 32 to 213 % when directly compared to stripe-patterned Au-FEs (at the same scale of groove and pit). An Au-FE prepared from a polycarbonate sheet from a Blu-ray disc read only memory (BD-ROM) as substrate displayed the best electrochemical performance towards reductive sensing of HO. The respective calibration plot, acquired at a working potential of −0.1 V vs. Ag/AgCl, covers the 0 to 10 mM hydrogen peroxide concentration range. The sensitivity is as high as 3.11 μA∙mM∙cm which is larger by a factor of 28 compared to flat gold electrodes, and the detection limit (at a signal-to-noise ratio of 3) is 6 μM. Therefore, the results confirm that the indented nanopattern on the Au-FE significantly increases the efficiency of electrochemical detection. Conceivably, the surface patterns and structures may be designed in order to tune sensitivity with respect to future applications of Au-FEs in diagnostics, agriculture, and environmental monitoring. [ABSTRACT FROM AUTHOR]

[Display omitted] • A chemisorbed sulfur adlayer was developed on Au electrode for hydrogen peroxide (HP) reduction in an alkaline medium. • The proposed electrode successfully sorted out the potential dependent breakdown of hydrogen peroxide in Au electrode. • The reduction involves 1st order kinetics in a dual step in the rotational mode, whereas a lone step in the static mode. • The proposed sensor maintained a broad spectrum of linearity (10–2000 µM) with its low limit of detection (6.0 µM). The sensitive detection of hydrogen peroxide (HP) on Au surface is quite challenging owing to the potential dependent decomposition of HP. The current study investigated the development of chemisorbed sulfur adlayer onto the surface of the polycrystalline gold electrode to attain electroreduction of hydrogen peroxide in an alkaline medium using cyclic voltammetry (CV), chronoamperometry, and square wave voltammetry (SWV) measurement techniques. The sulfur adsorbed layer significantly reduces the decomposition of hydrogen peroxide onto the Au (pc) electrode surface allowing the hydrogen peroxide reduction process to proceed. The kinetic diagnosis suggests that the reduction is mass transfer controlled process where electron transfer is the rate determining step in the concerned reduction reaction. The presented electrochemical sensor exhibited high sensitivity and a quick amperometric response to HP in the concentration range of 10–2000 μM, with a detection limit of 6.0 μM. [ABSTRACT FROM AUTHOR]

Biomarkers-based QCM-biosensors are suitable tools for the label-free detection of infectious diseases. In the current study, a QCM-biosensor was developed for the detection of HBsAg. Briefly, anti-HBsAg antibodies were covalently bound to the primary amines after PEI and thiolated-PEI surface modifications of gold-electrode. After RSM optimization, the statistical analysis revealed no significant difference between the immobilization yields of modified layers. Therefore, the PEI-modified QCM-biosensor was selected for further analysis. The PEI-surface was evaluated by FESEM, AFM, ATR-FTIR, and CA measurement. The surface hydrophilicity and its roughness were increased after PEI-coating. Also, FTIR confirmed the PEI-layering on the gold-surface. RSM optimization increased the antibody immobilization yield up to 80%. The QCM-biosensor showed noteworthy results with a wide dynamic range of 1–1 × 103 ng/mL, LOD of 3.14 ng/mL, LOQ of 9.52 ng/mL, and detection capability in human-sera, which were comparable with the ELISA. The mean accuracy of the QCM-biosensor was obtained at 91% when measured by the spike recovery test using human-sera. The biosensor was completely regenerated using 50 mM NaOH and 1% SDS. The benefits provided by the developed biosensor such as broad dynamic range, sensitivity, selectivity, stability, regenerate ability, and low cost suggest its potential application for the non-invasive and timely monitoring of HBV-biomarker. [Display omitted] • A QCM-biosensor was developed for the detection of Hepatitis B biomarker. • Two surface modifications were tested for antibody coupling. • The PEI-modified biosensor showed an easier procedure and good results. • The QCM-biosensor was comparable to the gold-standard method. [ABSTRACT FROM AUTHOR]

Albendazole (ABZ) is a widely used anthelmintic drug for the treatment of parasitic worms and other diseases. The bulk electrolysis reduction reaction of albendazole (ABZ) was carried out in ammonium bromide-acetonitrile solution under stirring conditions. The reduction of albendazole at gold electrode gave three non-reversible waves. The average value of the electron transfer coefficient (nα) was found to be 0.505. The measured diffusion coefficient (D) had a value of 0.143×10−8 cm2 s−1. The bulk electrochemical reduction of ABZ products were characterized using liquid chromatography-mass spectroscopy. Three cyclic voltammetry reduction waves were observed using a gold electrode and three chromatographic peaks were observed using liquid chromatography- Mass spectrometry. The observed results suggested that the second and third reduction steps occurred at the sulfur functional group of albendazole. [ABSTRACT FROM AUTHOR]

Silver ion deposition on gold and silver disc electrodes in nitrate aqueous solutions and in [EMIM][NTf 2 ] room-temperature ionic liquid were investigated by staircase voltammetry (SV) and square wave voltammetry (SWV). The kinetics of the Ag(I)/Ag couple in [EMIM][NTf 2 ] solutions prepared with AgNTf 2 depends both on their water content and the AgNTf 2 concentration. The electrochemical reaction is reversible in aqueous solutions and wet [EMIM][NTf 2 ] long exposed to the open air, while it is quasi-reversible in anhydrous [EMIM][NTf 2 ]. Silver ion deposition proceeds without 3D nucleation overvoltage only in acidic aqueous solutions and anhydrous [EMIM][NTf 2 ]. It is shown in particular that back-and-forth scans in SWV allow direct detection of relatively low nucleation overvoltage occurring in 1 M KNO 3 solution. The role of the metal-water interface was discussed, kinetic parameters for 0.1 M AgNTf 2 in anhydrous [EMIM][NTf 2 ] were determined by numerical simulation and theoretical conclusions on SV for metal ion deposition from high-resistive media previously published were checked. [ABSTRACT FROM AUTHOR]