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Graphite screen-printed electrodes (SPEs) were modified with gold nanoparticles (AuNPs) produced by electric spark discharge between the SPE and a gold-silicon eutectic alloy (eAu/Si) tip electrode, under atmospheric conditions at 1.2 kV DC using a fully automated procedure. The automation was based on a 3D positioning device, which allowed to precisely adjust the sparking distance and to achieve regular spacing of a predetermined number of sparks across the surface of SPEs (d = 3 mm) by controlling the movement of the eAu/Si tip. Moreover, the effect of voltage-time characteristics of the produced discharges on the morphological and electroanalytical properties of the sparked-modified SPEs was investigated by setting the values of capacitors in the high voltage multiplier cascade, and at the power supply output. It is shown that under specific variables the underlying carbon layer is not appreciably damaged by the spark discharges and does not contribute to electrochemical responses of sparked SPEs, i.e., the active electrode surface has been entirely covered by AuNPs. Sparked surfaces were extensively characterized by scanning electron microscopy and various electrochemical techniques, while the electroanalytical utility of eAu/Si-sparked SPE was investigated with ascorbic acid as a pilot analyte. Advanced electrocatalytic activity is documented by an extreme shift of ascorbate oxidation overpotential (Ep = 89 mV at eAu/Si-sparked SPE) with respect to both bare SPE (Ep = 503 mV) and bulk gold electrode (Ep = 358 mV). Simultaneous differential pulse voltammetric sensing of ascorbic and uric acids in human urine is also demonstrated.

We report on the straightforward preparation of gold nanoparticles (AuNPs) through a direct metal-to-substrate electric discharge at ambient conditions at 1.2 kV between the source metal (gold) and low-cost graphite screen-printed electrodes (SPEs). Considering that sparked nanoparticles are generated on the basis of an evaporation-condensation process, comparative experiments by using Au and a eutectic Au/Si (97/3 wt%) alloy were conducted. The so-modified sparked AuNP-SPE and eAuNP-SPE, respectively, were characterized by scanning electron microscopy, cyclic voltammetry, and electrochemical impedance spectroscopy (EIS). Data revealed a 2.4-fold electro active surface of AuNPs in the case of eAuNP-SPE. Compared with the unmodified SPEs, sparked electrodes exhibited two distinct electrode-electrolyte interfaces, characterized by different time-constants. EIS data were successfully modeled to an equivalent electric circuit that considers sparked-induced morphological features of the sensing surface and concomitant alterations of the diffusion process. Both types of sparked electrodes endowed sensitivity to otherwise inactive plain SPEs to the anodic stripping voltammetric detection of arsenic. Compared with AuNP-SPE, eAuNP-SPE exhibited ca. 5-fold sensitivity and offered fast (30 s preconcentration time) measurements, linear response over the concentration range from 0.5 to 12 ppb and a limit of detection (3σ/m criterion) of 0.22 ppb. Moreover, eAuNP-SPEs were successfully applied to the determination of arsenic in drinking water. Results demonstrated a new type of AuNP-modified low cost electrodes lend themselves to extremely simple preparation while offering enhanced detection capabilities and a wide-scope of applicability.

This work reports on a new bipolar electrochemistry based device for the detection of reducing compounds that are oxidized at the anode compartment of a “closed” bipolar electrode cell by recording the onset driving voltage at which an electrodeposited metal track, being visible by the unaided eye, is formed at the cathode pole. The concept is demonstrated for the determination of ascorbic acid and hydrogen peroxide by using an acidic solution of copper(II) chloride, while the underlying theory is explained. The onset driving voltage of the indication event (formation of the metal track) is found to be dependent on the concentration of the targets. Compared with the existing bipolar electrochemistry based analytical methods, the proposed method: i) introduces for the first time the onset driving potential as a measure of the target concentration, and ii) does not require extra instrumentation or devices for measuring the reporting event (intensity of emitted light, fluorescence or electrode’s length at the sub mm level). Along with its inherent advantages of low cost and simplicity it paves the way for the development of low-cost, portable analytical devices for reducing species and, potentially, for the development of biosensors based on oxidase enzymes.

Electrochemical deposition of the material released by anodizing nickel and copper nickel alloy in pure water onto carbon fiber microelectrodes was used to assemble miniature glucose sensors. The composition and morphology of the deposits was investigated by scanning electron microscopy, energy dispersive X-ray spectroscopy and X-ray photoelectron spectroscopy. The deposition of anode-derived materials proceeded by two consecutive mechanisms, which are explained in detail. The electrochemical properties of the designed electrodes were subsequently investigated by cyclic voltammetry and electrochemical impedance spectroscopy. The different Ni- and mixed CuNi-modified microelectrodes were examined as glucose sensors and the best performing electrodes based on the alloyed deposit exhibited very high sensitivity (5720 μA mM−1 cm−2), low detection limit (0.3 μM) and ability to quantify glucose in blood serum.

Graphite screen-printed electrodes (GSPEs) modified with tin nanoparticles (SnNPs) through a “green”, fast and extremely facile sparking process were used for the anodic stripping voltammetric determination of trace Cd and Zn. The effect of the magnitude of the energy dissipated during sparking events as well as other sparking parameters on the amount of the deposited tin, the morphology of the sparked surfaces and the electroanalytical properties of SnNP/GSPEs were investigated. Experiments were performed in the presence of bromide ions, which were used to enable well-resolved stripping peaks for cadmium. Other experimental variables, such as the pH of the supporting electrolyte, the square wave voltammetry parameters, the concentration of bromide ions, the deposition potential and the deposition time were also examined. Copper interference on Cd and Zn detection was effectively alleviated by the addition of ferrocyanide and gallium ions, respectively. Under selected conditions, the limits of detection, for a 2 min preconcentration time, were 0.5 μg L−1 Cd and 0.3 μg L−1 Zn. SnNP/GSPEs were successfully applied to the determination of Cd and Zn in tap and bottled water samples. Results suggest that sparked SnNP/GSPEs represent a new promising type of environmentally friendly sensors for the determination of Cd and Zn in the sub-microgram-per-liter level that surpass those previously given in the literature in terms of simplicity, cost, time, labor effort, waste loadings of the modification procedure, and low cost of the final sensor.

The construction of a cylindrical carbon fiber on-line detector is presented, featuring a novel way of sealing the carbon fiber microelectrode, the design of an interchangeable carbon fiber microelectrode-based flow cell and its interface with data-acquisition electronics. The two-electrode setup was used, where the regeneration of the carbon fiber working electrode surface between analyses was performed using an electrochemical procedure, typically −1/+1 V potential cycling. The detector was incorporated into the flow injection analysis manifold and the applicability of the developed sensing platform tested for monitoring a hexacyanoferrate (II/III) redox probe and the oxidizable compounds trolox (6-hydroxy-2,5,7,8-tetramethylchroman-2-carboxylic acid), uric acid, and l -ascorbic acid, with dehydroascorbic acid as a negative control. Finally, the optimized procedure was utilized for the analysis of human blood serum reductive (antioxidant) capacity based on amperometric sensing and flow injection analysis at a flow rate of 10 μl/min. Amperometric responses for blood serum samples were evaluated for standard deviation, whose average value was estimated to be ±0.3 nA (n = 20). The electrolytic efficiency of the detector was on the order of % units, e.g. 2% for trolox. The flow cell geometry and application of carbon fiber electrodes resulted in the absence of dead volumes and passivation phenomena, in contrast to conventional high-surface-area electrochemical cells. We suppose that the complex technical solution presented here could find a broad range of applications in the on-line monitoring of other reducing low-molecular bioactives and of the redox properties of various body fluids or clinical samples.

The development of sensors for diagnostic purposes is of immense importance. Despite the number of proposed sensors showing attractive detection capabilities, the widespread use of these sensors is mainly hindered by selectivity issues and the elaborate tailoring of the sensing surface that eventually increases both the cost of the final sensor and the individual analysis cost. Herein, we report on the development of an advanced sensor for 8−hydroxy−2ˊ−deoxyguanosine (8−OHdG), an important biomarker for DNA oxidative damage. The sensor was developed on a low-cost graphite screen-printed electrode (SPE) by employing for the first time, an extremely fast SPE-to-graphite “linear” mode sparking process that enables the uniform modification of the whole electrode surface in less than 20 s. Graphite-sparked SPEs exhibited a linear relationship with the concentration of 8−OHdG over the range 2–50 nM, while the limit of detection (3σ) was 0.35 nM. The sensors showed a notable resistance to interference by 1000-fold excess of dopamine and ascorbic acid, and 100-fold excess of uric acid. A simple treatment of the samples, based on uricase, that eliminates the interference caused by uric acid under real-world conditions (>1000-fold excess) was optimized and proposed. The method was successfully applied to the determination of 8−OHdG in synthetic urine samples. Recovery was 95%.

Bare and oxygen doped graphitic carbon nitride were synthetized by the thermal polymerization of melamine (CN-M) and the mechanical mixtures of melamine and cyanuric acid, respectively, at 550 °C for 4 h. The ratios of melamine and cyanuric acid were 1:0.5, 1:1 and 1:2 (CN-MCA1, CN-MCA2 and CN-MCA3). The content of oxygen increased from 1.88 wt% (CN-M) to 3.93 wt% (CN-MCA3) and the specific surface area increased from 14 to 41 m2 g−1. The prepared CN materials were characterized by the elemental analysis, UV-Vis diffuse reflectance, X-ray diffraction, Fourier transform infrared spectrometry, the physisorption of nitrogen, scanning electron and high-resolution transmission electron microscopy, X-ray photoelectron spectroscopy, the determination of zeta potentials, and the Mott-Schottky method. The addition of cyanuric acid led to partial changes in the CN morphology, as documented by occurrence of CN tubes, increase in the specific surface area and was a source of additional -O- and -OH moieties which modified the CN surface in addition to the spontaneous oxygenation observed in CN-M. The above effects positively influenced photocatalytic activity of the CN materials as demonstrated using Rhodamine B (RhB) and the Ofloxacin antibiotics. The photocatalytic decomposition of Ofloxacin was more efficient than that of RhB and differed in kinetics (first-order vs. zero-order reaction). The reusability and stability of the CN materials was verified by repeating batch photocatalytic decompositions of Ofloxacin experiments for five times.

Mechanical pencil leads were studied as disposable, low-cost electrodes. Lateral surfaces of mechanical pencil leads branded as “polymer” show high electron transfer rates for hexaamineruthenium chloride, potassium ferricyanide, ascorbate, ferric chloride and dopamine electrochemical probes, and are significantly better electrode materials than either classic woodcase clay–graphite pencil compositions or non-polymer mechanical pencil leads. Best polymer leads outperform glassy carbon, basal and edge graphite and boron-doped diamond electrodes. In addition to electrochemical experiments, the studied pencil leads were characterized by scanning electron microscopy, energy-dispersive X-ray spectroscopy and Raman spectroscopy. High content of sp3 hybridized carbon (up to 80%) with a low degree of surface oxidation and occurrence of silicon monoxide (SiO) on the surfaces of the polymer pencil leads were found using X-ray photoelectron spectroscopy. Low double layer capacitance values of similar magnitude as that found for boron-doped diamond electrodes are at the origin of favourably low background currents on the polymer pencil lead electrodes. SiO containing polymer pencil lead electrodes allow electrochemical analysis that is more sensitive than common carbon electrodes, as demonstrated by voltammetry of adenine and xanthine.

Here we report for the first time the development of a compact, closed bipolar electrochemistry (BPE) device for the determination of antioxidant capacity in real-world samples by recording the onset driving voltage at which an eye-visible reporting event at the cathode pole of bipolar electrode (BE) occurs. The BPE cell consists of two distinct anode and cathode compartments that are electrically connected through a platinum wire BE. The anode pole of the BE is covered by a cellulose acetate thin film to prevent the fouling of the surface, while the cathode pole is embedded into an agarose hydrogel containing phenolphthalein, i.e., an acid-base indicator. The method relies on the oxidation of the reducing compounds in the sample by a fixed amount of H2O2 and the electro oxidation of the remaining H2O2 in the anode pole of the BE. This reaction triggers the reduction of water at the cathodic pole accompanied by the production of hydroxyl ions at different, H2O2 concentration-dependent onset driving voltages. The resulting increase of pH at the cathode pole results in the formation of a pink spot (reporting event), which is visible by the unaided eye. The applicability of the BPE device for the determination of antioxidant capacity in fruit juices and sodas is demonstrated. The analytical results, expressed as Trolox (TEAC) or Vitamin C (CVEAC) equivalent antioxidant capacity, correlate well with those obtained by the CUPRAC method.

Sensitive analysis of nine selected antipsychotic drugs is demonstrated by high performance liquid chromatography coupled with innovative electrochemical detector employing the non standard, 0.2 mm diameter Pentel AinStein pencil graphite as a working electrode. In addition to low cost, the detector performance is characterized by low background current, capability to operate in low ionic strength media and very fast attainment of stable baseline. These advantageous features are attributed to microelectrode character of the pencil lead surface. The concentration LODs ranged between 1.0 (olanzapine) and 7.9 nmol/L (chlorpromazine) with linearity up to 500 nmol/L . Model analyses in spiked control serum as well as the real sample analyses of human plasma samples of subjects after intoxication with olanzapine resp. promethazine are shown. The developed method could be used for forensic monitoring of commonly used APs in blood samples. According to relevant assessment tools, the whole procedure can be regarded as green.

We report on facile generation of graphite nanomaterials (GNMs) with advanced electro catalytic properties through a direct electric discharge process between pencil leads and graphite screen − printed electrodes (SPEs) at ambient conditions at 1.2 kV. Various commercially available pencil leads of different degrees of hardness were examined. Sparked GNM − SPEs were characterized by Raman spectroscopy, SEM, CV, and EIS. Taking as criterion the highest response to the electro-reduction of nitro group of 2,4,6−trinitrotoluene (TNT) at −0.3 V at deoxygenated solutions, Castell 9000 (2B) pencil was selected as optimum. GNM − SPEs exhibited a linear response over the concentration range 1 − 100 ppb TNT, while the limit of detection (LOD) based on the 3σ/m criterion was calculated 0.44 ppb. The interference effect of other nitro − aromatic explosives and masking compounds, which are used to hinder the detection of TNT, was extensively investigated. The determination of TNT was also achieved by measuring the oxidation of the electrochemically generated hydroxylamine groups. In this format, each measurement was conducted with a new electrode polarized at −0.275 V for 2 min. At the cost of a slightly increased time of analysis, the anodic determination of TNT offered increased selectivity, applicability in non − deoxygenated solutions, linear response over the concentration range 1 − 50 ppb TNT and an LOD of 0.25 ppb. GNM − SPEs were successfully applied to the determination of TNT in spiked drinking water samples. Recovery was 101 − 108 %.

Despite their outstanding performance for the stripping voltammetric detection of trace metals, bismuth electrodes show poor sensitivity for the cathodic detection of organic compounds. Moreover, oxygen removal from samples is recommended to lower the background signal, which limits their application to on-site analysis. Herein, we propose recently introduced sparked-bismuth oxide screen printed electrodes for the cathodic detection of riboflavin, a reducible organic compound. The ultra-sensitive determination of riboflavin in the sub-nanomolar range in the presence of dissolved oxygen is demonstrated. After electroless preconcentration for 60 s, electrodes showed a linear response over the concentration range 1–100 nmol L−1 riboflavin, while the limit of detection (S/N = 3) was found to be 0.7 nmol L−1 riboflavin, ca. 140-fold lower than that has been achieved with electroplated bismuth electrodes. Excellent interelectrode reproducibility and application to a pharmaceutical sample are also demonstrated.

The electrochemical behavior of fesoterodine (FES), an antimuscarinic drug used for the treatment of urge incontinence and overactive bladder, was investigated using linear sweep and cyclic voltammetry at a stationary and rotating disc glassy carbon electrodes. A single two-electron anodic signal of FES was observed in neutral buffered aqueous methanolic solutions. Kinetics of alkaline hydrolysis of FES to its active metabolite 5-hydroxymethyl tolterodine was investigated by time dependent linear sweep voltammetry. Controlled potential electrolysis of FES solutions was performed at platinum gauze electrode in aqueous-methanolic media. Electrolyzed solutions were analyzed using ultra performance liquid chromatography with electrospray ionization quadrupole time-of-flight mass spectrometry. Two main products of electrochemical oxidation of fesoterodine were identified as 5-formyl fesoterodine (isobutyric acid 2-(3-diisopropylamino-1-phenyl-propyl)-4-formyl-phenyl ester) and N-desisopropylated fesoterodine (isobutyric acid 4-hydroxymethyl-2-(3-isopropylamino-1-phenyl-propyl)-phenyl ester). The mechanism of the electrochemical oxidation of FES has been proposed and confirmed using on-line electrochemistry/mass spectrometry with porous glassy carbon electrode.

We report that highly effective electrode modification can be achieved by sparking process between a flat electrode substrate and a tip counter electrode. The concept is introduced by the development of Bi2O3-modified graphite screen printed electrodes (SPEs). SPEs were sparked with a bismuth wire at 1.2 kV under atmospheric conditions. The effect of polarity on the morphology of the sensing surface, bismuth loading and the sensitivity of the resulting sensors for the simultaneous anodic stripping voltammetric determination of Cd(II) and Pb(II) was investigated. Compared with electroplated and various bismuth precursors bulk-modified SPEs, the developed sparked electrodes exhibited considerably lower limit of detection (0.2 μg L−1, S/N = 3) for each target ion. Therefore, sparking technique offers a facile and green approach for the development of highly sensitive bismuth-based electrodes, and a wide-scope of applicability in the development of metal-modified sensing surfaces. Keywords: Electric discharge, Spark deposition, Bismuth electrode, Toxic heavy metals, Stripping voltammetry, Screen printed electrode

The development of medical diagnostic devices for point-of-care applications (PoC) is a key demand towards the establishment of decentralized health-care systems. The cost of miniaturized transducers, the need for elaborated modification of the sensing surface and the complexity of the assay workflow impede the widespread use of current biosensing technologies to PoC applications. Herein, we describe a portable medical diagnostic device (we call it “BioPoC”), which employs free-standing enzyme-modified responsive polymer membrane-based biosensors and a newly devised low-cost transduction principle. The device includes a single vertical channel with an integrated sample dosing well. Its operation is based on the measurement of the time required the originally infinite electric resistance between two, separated by the enzyme-modified responsive polymer membrane, conductive strips to reach a finite value (typically R20MOhm) is proportional to the concentration of the target. By proper combination of different responsive polymers and enzyme(s), BioPoC device can enable the drop-volume, one-step biosensing of a variety of biomarkers. Data demonstrate an outstanding selectivity against the components of the matrix, while the detection range can be tuned over the normal range of the analyte of interest. As part of the proof-of-concept, BioPoC device was employed for the determination of urea in undiluted human urine and the near-patient detection of Helicobacter pylori in gastric antrum bioptic samples.

This work describes the development of a “green” electrocatalytic surface based on molybdenum-sparked screen-printed graphite electrodes (sparked Mo-SPEs) for the voltammetric determination of azo synthetic colorants. Sparked Mo-SPEs were produced by an in-situ, liquid-free metal-to-SPE electric discharge approach at 1.2 kV under atmospheric conditions. Morphological studies with scanning electron microscopy and energy dispersive X-ray spectroscopy revealed the formation of Mo nanoparticles that have been evenly distributed over the entire surface of the electrodes. X-ray photoelectron spectroscopy showed that the atomic percentage of Mo over the electrode surface is only 0.5 ± 0.1% in the form of metallic Mo (25.3%) and Mo(VI) (74.7%). In 0.1 M acetate buffer solution, pH 5 sparked Mo-SPEs exhibited well-defined oxidation peaks at 0.730 V for sunset yellow (SY) and 0.973 V for tartrazine (TAR) versus Ag/AgCl/3 M KCl. Sparked Mo-SPE demonstrated remarkably increased responses compared with plain or electrodeposited MoxOy modified-graphite SPEs and enabled the simultaneous determination of the targets in the nano molar range. Under selected experimental variables a linear calibration curve over the concentration range from 5 to 250 nM SY/TAR was constructed. The limits of detection (S/N 3) were 2 nM. The response of Mo-SPE in the presence of other azo colorants was also investigated. The developed electrodes were successfully applied to the determination of SY and TAR in real-world samples. The accuracy of the method was established by recovery studies. Recovery was between 94–109%.

A concentric thin layer cell accommodating a non-standard 0.2 mm diameter pencil graphite disposable working electrode is described. The cell was installed into HPLC manifold as an electrochemical detector. Trouble-free operation in mobile phases containing both low and high content of organic solvents is demonstrated by HPLC analyses of phenolic acids and tocopherol isomers. The data obtained from HPLC separation of model mixtures of gentisic, caffeic and dihydrocaffeic acids show a remarkable electrolytic efficiency exceeding 80% at 200, and 50% at 500 μL min−1, while for gentisic acid the limit of detection (LOD) was 0.4 nmol L−1 at 20 microliter sample loading (8 fmol on-column). Similar performances were found in non-aqueous mobile phase, where a LOD of 0.8 nmol L−1 was achieved for delta-tocopherol. The developed flow-through detector is designed to allow easy replacement of pencil graphite working electrode in a highly reproducible manner. The relative standard deviation for the HPLC analysis of tocopherol isomers was of 5.3% (n = 3, C = 500 nmol L−1). The combination of simple construction, excellent electrochemical performance and hydrodynamics identical to that of commercial UV-VIS HPLC detector suggests that the proposed device is a viable low-cost alternative to commercially available electrochemical detectors.

International audience; Besides the well-known chemoprotective effects of polyphenols, their prooxidant activities via interactions with biomacromolecules as DNA and proteins are of the utmost importance. Current research focuses not only on natural polyphenols but also on synthetically prepared analogs with promising biological activities. In the present study, the antioxidant and prooxidant properties of a semi-synthetic flavonolignan 7-O-galloylsilybin (7-GSB) are described. The presence of the galloyl moiety significantly enhances the antioxidant capacity of 7-GSB compared to that of silybin (SB). These findings were supported by electrochemistry, DPPH (2,2-diphenyl-1-picrylhydrazyl) scavenging activity, total antioxidant capacity (CL-TAC) and DFT (density functional theory) calculations. A three-step oxidation mechanism of 7-GSB is proposed at pH 7.4, in which the galloyl moiety is first oxidized at Ep,1=+0.20V (vs. Ag/AgCl3M KCl) followed by oxidation of the 20-OH (Ep,2=+0.55V) and most probably 5-OH (Ep,3=+0.95V) group of SB moiety. The molecular orbital analysis and the calculation of O-H bond dissociation enthalpies (BDE) fully rationalize the electrooxidation processes. The metal (Cu(2+)) complexation of 7-GSB was studied, which appeared to involve both the galloyl moiety and the 5-OH group. The prooxidant effects of the metal-complexes were then studied according to their capacity to oxidatively induce DNA modification and cleavage. These results paved the way towards the conclusion that 7-O-galloyl substitution to SB concomitantly (i) enhances antioxidant (ROS scavenging) capacity and (ii) decreases prooxidant effect/DNA damage after Cu complexation. This multidisciplinary approach provides a comprehensive mechanistic picture of the antioxidant vs. metal-induced prooxidant effects of flavonolignans at the molecular level, under ex vivo conditions.

A method has been developed for measuring and evaluating the overall antioxidant activity derived from the low-molecular weight antioxidants (scavengers). The principle governing this method is based on a common chemical characteristic of the scavengers, their reducing properties. It was hypothesized and then demonstrated that an evaluation of the overall reducing power of a biological sample correlates with the overall scavenging activity of the sample. In order to quantify the total reducing power, the cyclic voltammetry methodology was applied. The resulting measurements correlated with the antioxidant activity of both hydrophilic and lipophilic scavengers. The method is suitable for use in biological fluids and in tissue homogenates, and can supply information concerning the type of antioxidants and their total concentration without having to determine specific compounds. A noninvasive procedure for determining skin overall scavenging activity is also described. This method is based on a well containing an extraction solution that is attached to the skin's surface. Following incubation time the extraction solution is analyzed using the cyclic voltammeter instrument and other methods. We have found these methods suitable for evaluating the reducing capacity status in various clinical conditions such as diabetes, ionizing and nonionizing irradiation, brain degenerative diseases, head trauma, and inflammatory bowel diseases. This method is also an efficient tool for evaluating the overall antioxidant capacity of mixtures of antioxidant preparations in vitro. The measurements themselves are simple and rapid. Furthermore, they do not require manipulation of the samples.