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In the present paper, TiO 2 nanoparticles were utilized to modify the gold electrode surface and to emphasize a useful technique for determination of a food dye, erythrosine. The utilized modifier was characterized by Scanning electronic microscopy (SEM), and X-ray diffraction (XRD) analysis. In the first portion of the work, the oxidation properties of the dye were examined at different pH ranging from 3.0–11.2, varying accumulation time and at different scan rates, by using the cyclic voltammetric technique. The number of electrons and protons involved in the reaction, and heterogeneous rate constant were calculated. The second portion of the work includes the appositeness of the estimated method for the detection of the dye in trace level by utilizing differential pulse voltammetric technique. In optimum conditions (supporting electrolyte pH, accumulation time, modifier amount) the peak current was proportional to the concentration in the range 0.1 μM–10.0 μM with detection limit 2.6 nM. The applicability of the proposed method was achieved for food industries as well as for environmental applications. [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 anodic voltammetric behavior of an antibiotic drug, lincomycin hydrochloride (LIN) at gold electrode (GE) has been investigated using cyclic and linear sweep voltammetry. The dependence of the current on pH, concentration and scan rate were investigated to optimize the experimental conditions for the determination of lincomycin. The anodic peak was characterized and the process was adsorption-controlled. The number of electrons transferred in the oxidation process was calculated. In the range of 8.0 × 10-6 to 1.0 × 10-4 M, the current measured by linear sweep voltammetry presents a good linear property as a function of the concentration of lincomycin with a detection limit of 1.7 × 10-7 M with good selectivity and sensitivity. The proposed method was successfully applied to lincomycin determination in pharmaceutical dosage form and in urine as a real sample. This method can be employed in clinical analysis, quality control and routine determination of drugs in pharmaceutical formulations. [ABSTRACT FROM AUTHOR]

Determination of fluoroquinolones (FQs) in foodstuffs and environment is of great importance. In this study, a novel electrochemical sensing method was developed for rapid, highly sensitive and specific detection of FQs, based on aptamer (Apt) as molecular recognition probe, single-stranded DNA-binding protein (SSB) as a physical and negatively charged barrier for the access of redox probe ([Fe(CN) 6 ] 3−/4− ) to the surface of gold electrode. The designed electrochemical aptasensor needs less than 1 h for detection of ciprofloxacin. In the absence of ciprofloxacin, SSB interacts with Apt and restricts the access of redox probe to the surface of electrode, leading to a weak current signal. In the presence of target, SSB could not bind to the Apt, resulting in more access of redox probe to the surface of electrode and a strong current signal. The designed electrochemical sensor exhibited high specificity toward FQs with a limit of detection (LOD) as low as 263 pM for ciprofloxacin. Moreover, the developed sensing method was successfully applied for determination of ciprofloxacin in serum, milk and water samples with LODs of 336, 351 and 261 pM, respectively. [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]

In present work, we have developed a highly sensitive biosensor to evaluate the freshness of fishes by determining their xanthine level. This is based on xanthine oxidase (XOx) immobilized on the nanocomposite platform of titanium dioxide nanoparticles and multi-walled carbon nanotubes (TiO/MWCNT). The biosensor exhibited excellent performances like linear relation in the range from 0.5 to 500 μM, detection limit of 0.5 μM (S/ N = 3), and a rapid response time of 30 s. The biosensor showed excellent reproducibility, high selectivity, and long-term stability (60 days). The techniques like dynamic light scattering (DLS), scanning electron microscopy (SEM), electrochemical impedance spectroscopy (EIS), cyclic voltammetry (CV), and X-ray diffraction (XRD) were used to characterize the nanocomposite modified electrode. The current biosensor is very reliable and stable for the determination of the freshness of fishes. [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]

Osmium tetroxide bipyridine ([OsO4(bpy)]) is a versatile label for DNA electrochemistry. Here we report our efforts to create an osmium tetroxide-labeled immobilized DNA probe for use in biosensing experiments. Our label is applied in-house, as opposed to many other covalent redox labels used with DNA. We developed an on-electrode labeling method that was able to avoid attack of our disulfide-based linker by the [OsO4(bpy)]. Our results include two different hairpin-based signal-off hybridization detection assays, each with robust, reproducible signal decrease on binding to complementary target. We also found that 6-mercapto-1-hexanol was able to interact with [OsO4(bpy)] in a stable manner when assembled at the surface, but was able to remove excess [OsO4(bpy)], which was found to adsorb strongly to the gold surface, and avoid MCH transformation, when applied after the labeling process. Furthermore, we found an increased adsorption affinity of [OsO4(bpy)]-labeled DNA onto gold, characterized the redox behavior of adsorbed [OsO4(bpy)], and determined voltammetric signals on the HMDE of our intact disulfide linker while verifying that this linker is attacked by [OsO4(bpy)] when in solution. [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]

An electrochemical sensor for nonenzymatic hydrogen peroxide (H 2 O 2 ) detecting based on size controllable preparation of gold nanoparticles (Au) loading on graphene sheets@cerium oxide (GS@CeO 2 ) nanocomposites modified gold electrode (GE) was fabricated. The GS@CeO 2 nanocomposites were prepared via a facile solvothermal process. Different sizes of Au were controllably prepared and homogenously loaded on the surface of GS@CeO 2 nanocomposites modified GE using a simple electroless plating method. X-ray powder diffractometer (XRD) combines with Fourier transform infrared spectrum (FTIR) were used to characterize the composition of GS@CeO 2 nanocomposites. Electrochemical impedance spectroscopy (EIS) was utilized to study the interfacial properties as well as Field emission scanning electron microscopy (FESEM) was employed to characterize the morphologies of different electrodes. The electrochemical properties of electrochemical sensor were investigated by cyclic voltammetry (CV) and i-t curve methods. After all experimental parameters were optimized, the GS@CeO 2 /Au hybrid nanomaterials modified GE (GE ǀ GS@CeO 2 /Au) showed a good performance towards the electrocatalytic reduction of H 2 O 2 . A wide linear detection range (LDR) of CV peaks from 1.0 × 10 −3 mM to 10.0 mM ( R 2 = 0.9990) and a low limit of detection (LOD) of 2.6 × 10 −4 mM (S/N = 3) was achieved. The proposed electrochemical sensor was quick, selective, sensitive, simple, stable and reliable to quantitative determination of trace H 2 O 2 in contact lens care solutions. [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]

Mycobacterium tuberculosis is an infectious agent that causes tuberculosis (TB). TB is one of the major causes of death worldwide, mainly in the developing country. Early and rapid diagnosis of TB will be of great help to isolate the patients and control the disease. The aim of this research is to detect Mycobacterium tuberculosis using voltammetric DNA biosensor by using gold electrode modified by self assembled monolayer with thiol. Single-stranded probe DNA was immobilized on the surface of self assembled monolayer gold electrode with the assistance of cysteamine and glutaraldehyde, which was further used to hybridize with the target DNA sequence and non-complementary target sequence. Differential Pulse Voltammetry (DPV) was used to study the immobilization of DNA probe and hybridization with the target DNA. The hybridization reaction on the gold electrode surface was detected by monitoring a guanine oxidation signal at +0.2 Volt. Voltammetric DNA biosensor using gold electrode modified with thiol can be used to determine hybridization between probe DNA and target DNA sequence of M. tuberculosis with sensitivity value is 0.5175 for target DNA in concentration range 0- 30 μg/mL; detection limit is 2.7046 μg/mL and quantification limit is 9.0155 μg/mL, accuracy is 99.22%, precision 99.86% [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]

Herein, we report a simple and inexpensive way for the fabrication of an ultramicroelectrode and present its characterization by electrochemical techniques. The fabrication of polyaniline UME involves only two steps: modification of a gold (Au) electrode by self assembled monolayers (SAM) and then electrodeposition of polyaniline film on this thiol-coated Au electrode by using cyclic voltammetry and constant potential electrolysis methods. Two types of self-assembled monolayers (4-mercapto-1-butanol, MB, and 11-mercaptoundecanoic acid, MUA) were used, respectively, to see the effect of chain length on microelectrode formation. Microelectrode fabrication and utility of the surface was investigated by cyclic voltammetric measurements in a redox probe. The thus prepared polyaniline microelectrode was then used for DNA immobilization. Discrimination between double-stranded DNA (dsDNA) and single-stranded DNA (ssDNA) was obtained with enhanced electrochemical signals compared to a polyaniline-coated Au electrode. Different modifications on the electrode surfaces were examined using scanning electron microscopy (SEM).

The electrochemical behaviors of thiazolidine (tetrahydrothiazole) on gold and platinum electrodes were investigated in a Britton-Robinson buffer (pH 2.77–11.61), acetate buffer (pH 4.31), phosphate buffer solutions (pH 2.11 and 6.38) and methanol or acetonitrile containing various supporting electrolytes. Detection was based on a gold wire electrochemical signal obtained with a supporting electrolyte containing 20% methanol-1.0 mM of phosphate buffer (pH 6.87, potassium dihydrogen phosphate and dipotassium hydrogen phosphate) as the mobile phase. Comparison with results obtained with a commercial amperometric detector shows good agreement. Using the chronoamperometric sensor with the current at a constant potential, and measurements with suitable experimental parameters, a linear concentration from 0.05 to 16 mg L−1 was found. The limit of quantification (LOQ) of the method for thiazolidine was found to be 1 ng.

The aim of our work was to synthetize of a new analogue of abiraterone—thiolated abiraterone (HS-AB) and design a gold surface monolayer, bearing in mind recent advances in tuning monolayer structures and using them as efficient drug delivery systems. Therapeutic self-assembled monolayers (TSAMs) were prepared by chemically attaching HS-AB to gold surfaces. Their properties were studied by voltammetry and atomic force microscopy (AFM). A gold electrode with immobilized thioglycolic acid (HS-GA) was used for comparison. The surface concentration of HS-AB on the gold surface was 0.572 nmol/cm2, determined from the area of the voltammetric reduction peaks (desorption process). The area per one molecule estimated from the voltammetry experiments was 0.291 nmol/cm2. The capacity of thus prepared electrode was also tested. The calculated capacity for the HS-AB modified electrode is 2.90 μF/cm2. The obtained value indicates that the monolayer on the gold electrode is quite well ordered and well-packed. AFM images show the formation of gold nanoparticles as a result of immersing the HS-AB modified gold electrode in an aqueous solution containing 1 mM HAuCl4·3H2O. These structures arise as a result of the interaction between the HS-AB compound adsorbed on the electrode and the AuCl4− ions. The voltammetric experiments also confirm the formation of gold structures with specific catalytic properties in the process of oxygen reduction.

Herein we exploit the molecular engineering capability to immobilize monolayer of polyamidoamine dendrimer on gold electrode, which exhibit enhanced charge transfer and biocompatibility. Polyamidoamine (PAMAM generation 5.0) dendrimers were used as template/stabilizers for gold nanoparticle growth, with Au@PAMAM nanoparticles serving as surface modifier to produce monolayer film. TEM, UV-vis spectroscopy, and AFM were used to characterize the formation of monolayer Au@PAMAM on gold surface. The cyclic voltammetry (CV) and Impedance measurements of Au@PAMAM modified gold electrodes demonstrate electrochemistry properties of modified electrode. Furthermore, Au@PAMAM coating can greatly increased the biocompatibility of gold electrode as determined by cell growth curves

Using the cyclic voltammetry, it has been shown that hydrogen evolution at a gold electrode is necessary in the electrochemical activation of azithromycin dihydrate and erythromycin A. After four hours of the potential holding at –1.2 V vs. SCE, the pH of the electrolyte has been changed from 8.40 to 8.96; from 8.40 to 8.77 in the presence of erythromycin A, and from 8.40 to 9.18 in the presence of azithromycin, indicating the reaction of the hydrogen species with antibiotics. This effect has been confirmed by using the phenolphthalein indicator and by analysing colours of the solutions by UV-Vis, as well as by FTIR spectroscopy. Under the identical experimental conditions at the gold electrode, in contrast to azithromycin dihydrate and erythromycin A, roxithromycin and midecamycin electroactivity promotion has been obtained during the first forward sweep starting from the area of a double layer region.

A gold electrode was used for the qualitative and quantitative electrochemical determination of analytical methomyl in a neutral electrolyte (0.050 M NaHCO3) using cyclic linear sweep voltammetry. In the potential range from –800 mV vs. SCE to 1000 mV vs. SCE the analytical methomyl was quantitatively determined in the concentration range 4.0–16 mg L-1. In the potential range from ‑1300 mV vs. SCE to 1300 mV vs. SCE, methomyl was qualitatively determined by two anodic and four cathodic reactions. Cycling the potential in this range for 150 min caused the degradation of the molecule, which was confirmed by HPLC analysis. On the other hand, technical methomyl exhibited an inhibition of the gold electrode surface due to the impurities.

A gold electrode was used for the qualitative and quantitative electrochemical determination of analytical methomyl in a neutral electrolyte (0.050 M NaHCO3) using cyclic linear sweep voltammetry. In the potential range from -800 mV vs. SCE to 1000 mV vs. SCE the analytical methomyl was quantitatively determined in the concentration range 4.0-16 mg L-1. In the potential range from -1300 mV vs. SCE to 1300 mV vs. SCE, methomyl was qualitatively determined by two anodic and four cathodic reactions. Cycling the potential in this range for 150 min caused the degradation of the molecule, which was confirmed by HPLC analysis. On the other hand, technical methomyl exhibited an inhibition of the gold electrode surface due to the impurities.

The study of coverage (nmol/cm-2) of N-bencyl-1-cyclopenten-di-thiocarboxylic acid (novel compound) depending on the immersion time of the gold electrode in a solution of the mentioned compound, as well as the characterization of the adsorbed monolayer has been carried out by cyclic voltammetry (CV). The self assembled monolayer (SAM) has been tested for stability in defined potential intervals and blocking properties for electron transfer [Fe(CN)6]3-/[Fe(CN)6]4- and Cu(II). Detection and quantifying of copper by stripping of underpotential deposits and by stripping of bulk deposition formed at the modified gold electrode was carried out by square wave voltammetry (SWV) in copper-free phosphate buffer.

Abstract In this article, we reported a novel experiment results on Ag-doped DNA conductor in transverse direction.I–Vcharacteristics were measured and the relative conductances were calculated for different silver ions concentrations. With the increase of the concentration of silver ions, the conductive ability of DNA risen rapidly, the relative conductance of DNA enhanced about three magnitudes and reached a stable value when Ag+concentration was up to 0.005 mM. In addition, Raman spectra were carried out to analyse and confirm conduction mechanism.

The electrochemical behavior of N-nitrosothiazolidine carboxylic acid (NTAC) on gold and hanging mercury electrodes, using the cyclic and square wave voltammetries, was studied. Whereas NTAC suffer reduction in a single step on the mercury electrode, two peaks appears on the cyclic voltammograms on the gold electrode, one anodic peak overlaying the gold oxide process at 1.2 V and one cathodic peak at -0.41 V vs Ag/AgCl, KCl 3.0 mol L-1. The cathodic peak depends on the previous oxidation of NTAC at the electrode surface, presents irreversible and adsorption controlled characteristics and it is suitable for quantitative purposes.

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]

The aim of the present study is to present the different reactivity of azithromycin and clarithromycin (pure and commercial) at a gold electrode in neutral electrolyte using cyclic linear sweep voltammetry under the same experimental conditions. A gold electrode was successfully used for the electrochemical qualitative and quantitative determination of azithromycin dihydrate and azithromycin from capsules (Hemomycin®) and for the separation of azithromycin from one of the excipients, lactose monohydrate. The good catalytically activity of the gold electrode was employed only for the qualitative electrochemical determination of pure clarithromycin by appearance of one cathodic and four anodic reactions, which enabled structural changes in this molecule during electrochemical reactions to be studied. Commercial clarithromycin, Clathrocyn® was qualitative determined by one reproducible anodic reaction. The activity of one of the excipients, Avicel, observed as a cathodic peak at different potential from the cathodic peak obtained with pure clarithromicin was used for the determination of its presence in Clathrocyn® tablets. FTIR Analysis showed the apparent changes in structure of pure clarithromycin, as well as in the molecule of clarithromycin in Clathrocyn® tablets. HPLC Analysis showed a significant decrease in the concentration of azithromycin, Hemomycin® clarithromycin and Clathrocyn® after the electrochemical reactions.

The interaction of neutral red (NR) with single or double stranded DNA was investigated on ssDNA or dsDNA modified gold electrode. DNA was covalently immobilized on the surface of mercaptoethanol self-assembled gold electrode through the carboxylate ester as linkage between the 5’-NH2 end of DNA and -OH group of mercaptoethanol self-assembled monolayer with the help of 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide (EDC) and N-hydroxysuccinimide (NHS). The electrochemical behaviors of NR on DNA modified electrode were carefully investigated by cyclic voltammetry. NR was bound with ssDNA by electrostatic force but intercalation with dsDNA. The binding constant was calculated as 8.95×103 M-1 and 2.15×104 M-1 respectively. The different responses of NR with ssDNA and dsDNA were further proved by UV-Vis absorption spectrophotometry and the results suggested that NR could be served to distinguish the ssDNA and dsDNA.

The aim of the present study is to present the different reactivity of azithromycin and clarithromycin (pure and commercial) at a gold electrode in neutral electrolyte using cyclic linear sweep voltammetry under the same experimental conditions. A gold electrode was successfully used for the electrochemical qualitative and quantitative determination of azithromycin dihydrate and azithromycin from capsules (Hemomycin®) and for the separation of azithromycin from one of the excipients, lactose monohydrate. The good catalytically activity of the gold electrode was employed only for the qualitative electrochemical determination of pure clarithromycin by appearance of one cathodic and four anodic reactions, which enabled structural changes in this molecule during electrochemical reactions to be studied. Commercial clarithromycin, Clathrocyn® was qualitative determined by one reproducible anodic reaction. The activity of one of the excipients, Avicel, observed as a cathodic peak at different potential from the cathodic peak obtained with pure clarithromicin was used for the determination of its presence in Clathrocyn® tablets. FTIR Analysis showed the apparent changes in structure of pure clarithromycin, as well as in the molecule of clarithromycin in Clathrocyn® tablets. HPLC Analysis showed a significant decrease in the concentration of azithromycin, Hemomycin® clarithromycin and Clathrocyn® after the electrochemical reactions.

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]

Due to the negative impact of nitrate and nitrite on human health, their presence exceeding acceptable levels is not desired in foodstuffs. Thus, nitrite determination at low concentrations is a major challenge in electroanalytical chemistry, which can be achieved by fast, cheap, and safe electrochemical sensors. In this work, the working electrode (Au) was functionalized with p-aminothiophenol (p-ATP) and modified with gold nanoparticles (Au-NPs) to manufacture the final (Au/p-ATP-Aunano) electrode in a two-step procedure. In the first step, p-ATP was electropolymerized on the electrode surface to obtain a polyaminothiophenol (PATP) coating. In the second step, Au/p-ATP-Aunano working electrode was prepared by coating the surface with the use of HAuCl4 solution and cyclic voltammetry. Determination of aqueous nitrite samples was performed with the proposed electrode (Au/p-ATP-Aunano) using square wave voltammetry (SWV) in pH 4 buffer medium. Characteristic peak potential of nitrite samples was 0.76 V, and linear calibration curves of current intensity versus concentration was linear in the range of 0.5-50 mg⋅L-1 nitrite with a limit of detection (LOD) of 0.12 mg⋅L-1. Alternatively, nitrite in sausage samples could be colorimetrically determined with high sensitivity by means of p-ATP-modified gold nanoparticles (AuNPs) and naphthylethylene diamine as coupling agents for azo-dye formation due to enhanced charge-transfer interactions with the AuNPs surface. The slopes of the calibration lines in pure NO2- solution and in sausage sample solution, to which different concentrations of NO2- standards were added, were not significantly different from each other, confirming the robustness and interference tolerance of the method. The proposed voltammetric sensing method was validated against the colorimetric nanosensing method in sausage samples. [ABSTRACT FROM AUTHOR]

We describe an electrochemical aptasensor for the amino acid homocysteine (hCys). A gold electrode was modified with a highly specific aptamer against hCys (a 66-base DNA oligonucleotide) acting as the recognition probe. The method is highly selective over cysteine and methionine. The effects of accumulation time, type and concentration of accumulation buffer and pH, type and concentration of stripping buffer were studied. Under optimized conditions and a working potential of 1.07 V (vs. Ag/AgCl), the response to hCys is linear in the 0.2 to 10 μM concentration range. The detection limit is 10 nM, and the relative standard deviation is 3.1 % (at 1 μM of hCys). The electrode can be regenerated by immersing it into a 3 M solution of urea solution. The method was applied to the determination of hCys in (spiked) serum and urine and gave recoveries of 88.5 and 96.5 %, respectively. [Figure not available: see fulltext.] [ABSTRACT FROM AUTHOR]