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Salivary thiocyanate is a biomarker of individual health that notably allows for the discrimination between smokers and non‐smokers. Recent studies have also demonstrated its potential as a biomarker of cystic fibrosis, thus rendering the development of methods for its determination in saliva of immense importance. In response, we report on the development of graphite screen‐printed electrodes (SPE) modified with cobalt(II) phthalocyanine nanosticks (CoPcNst), as low‐cost and semi‐disposable sensors for the determination of thiocyanate ion (SCN−) in human saliva. CoPCNst were synthesized and characterized using scanning electron microscopy, x‐ray diffraction, as well as infrared and Raman spectroscopies. The results revealed a structural proximity to the recently identified J‐polymorph. Compared with the electrode modified with commercial, beta‐structure cobalt(II) phthalocyanine, the CoPc Nst/SPE provided four times better LOD and LOQ (0.49 and 1.62 μM) for thiocyanate determination by differential pulse voltammetry. The response was linear up to 20 μM SCN− (R2=0.996) and it was not affected by excess of common electro active compounds, such as ascorbic and uric acid. The analytical utility of CoPc Nst/SPE in human saliva is demonstrated. [ABSTRACT FROM AUTHOR]

Abstract: The development of a preconcentrating sensor based on 6-O-palmitoyl-l-ascorbic acid (PAA)-modified graphite (GRA) electrodes for the determination of uranium is described. PAA, a water insoluble compound of ascorbic acid, was immobilized onto the surface of the GRA electrodes through physical adsorption from acetone solutions. Uranium was accumulated by heterogeneous complexation (10min, in 0.1M H3BO3, pH 4.3) and then, it was reduced by means of a differential pulse voltammetric scan in 0.1M H3BO3, pH 3.4. Alternatively, the performance of both preconcentration and voltammetric steps in a single run, at 0.1M H3BO3, pH 3.65, was also examined; however, in this case the observed current signals were lower by 30%. The experimental variables were investigated and under the selected conditions, a linear calibration curve in the range 2.7–67.5μgL−1 U(VI) was constructed (r 2 =0.9981). The 3σ limit of detection and the relative standard deviation of the method were 1.8μgL−1 U(VI) and 8% (n =5, 20μgL−1 U(VI), preconcentration time 10min), respectively. By increasing the preconcentration time to 30min, a limit of detection as low as 0.26μgL−1 U(VI) can be achieved. The effect of potential interferences was also examined. The accuracy of the method was established by recovery studies in inoculated tap and lake water samples. A simple and fast procedure based on filtering of the sample through a C-18 microcolumn was successfully used to remove the organic matter from the lake water samples. [Copyright &y& Elsevier]

The development of all-solid-state potentiometric ion selective electrodes for monitoring of ascorbic acid, by using a screen-printed compatible solid contact is described. The applied methodology is based on the use of PVC membrane modified with some firstly-tested ionophores (triphenyltin(IV)chloride, triphenyltin(IV)hydroxide and palmitoyl-l-ascorbic acid) and a novel one synthesized in our laboratory (dibutyltin(IV) diascorbate). Synthesis protocol and some preliminary identification studies are given. A conductive graphite-based polymer thick film ink was used as an internal solid contact between the graphite electrode and the PVC membrane. The presence and the nature of the solid contact (plain or doped with lanthanum 2,6-dichlorophenolindophenol (DCPI)) seem to enhance the analytical performance of the electrodes in terms of sensitivity, dynamic range, and response time. The analytical performance of the constructed electrodes was evaluated with potentiometry, constant-current chronopotentiometry and electrochemical impedance spectroscopy (EIS). The interference effect of various compounds was also tested. The potential response of the optimized Ph3SnCl-based electrode was linear against ascorbic acid concentration range 0.005–5.0 mM. The applicability of the proposed sensors in real samples was also tested. The detection limit was 0.002 mM ascorbic acid (50 mM phosphate, pH 5 in 50 mM KCl). The slope of the electrodes was super-Nernstian and pH dependent, indicating a mechanism involving a combination of charge transfer and ion exchange processes. Fabrication of screen-printed ascorbate ISEs has also been demonstrated. [Copyright &y& Elsevier]

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. [ABSTRACT FROM AUTHOR]

• "Linear" mode 2D-sparking process: Green, liquid free, and fast. • Uniform modification of the whole electrode surface in less than 20 s. • Outstanding resistance to interference by 1000-fold excess of dopamine, AA, and UA. • Complete removal of UA facilitates the determination of a few nM 8-OHdG in urine. 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 (3 σ) 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%. [Display omitted] [ABSTRACT FROM AUTHOR]

Abstract: The present work reports for the first time on the synthesis, characterization and performance of vanadium hexacyanoferrate (VHCF) as electrocatalyst of hydrogen peroxide. VHCF was synthesized by mixing V2O5 · nH2O xerogel with ascorbic acid and K4[Fe(CN)6] in double distilled water. X-ray powder diffraction, energy dispersive spectroscopy, scanning electron microscopy, and IR-spectroscopy data suggest the formation of nanocrystalline (mean crystal size∼11nm) compound with a tentative molecular formula K2(VO)3[Fe(CN)6]2. Composite films of VHCF with poly(vinyl alcohol) were developed over a glassy carbon electrode, and then covered with different (neutral, positively or negatively charged) membranes. The effect of each membrane on the working stability of the resultant sensors was evaluated. Cyclic voltammetry experiments showed that composite films exhibit a pair of reversible redox peaks, and a remarkable low potential electrocatalysis on both the reduction and oxidation of hydrogen peroxide. A linear calibration curve over the concentration range 0.01–3.0mM H2O2 was constructed. Limit of detection (S/N =3) of 4μM H2O2 was calculated. The proposed transducer is quite selective to hydrogen peroxide. No response was observed in the presence of 10mM ascorbic acid. [Copyright &y& Elsevier]

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 H 2 O 2 and the electro oxidation of the remaining H 2 O 2 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, H 2 O 2 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. Image 1 • A compact bipolar electrochemistry device using a liquid free catholyte is described. • The device enables the determination of antioxidant capacity in real samples. • The results correlate well with those obtained by the CUPRAC method. [ABSTRACT FROM AUTHOR]

Abstract: A comparative study regarding the electrocatalytic activity of graphene oxide (GO), chemically-reduced graphene oxide (crGO) and graphene produced by direct liquid exfoliation (dG) is presented. Sensors were developed by modifying glassy carbon (GC) electrodes with GO, crGO and dG and ascorbic acid was used as a pilot analyte. GC/GO electrodes offer substantially lower oxidation overpotential, up to 350mV, compared with GC/crGO, GC/dG and unmodified GC electrodes. In addition, the different carbon-to-oxygen atomic ratios in GO, as it occurs depending on the synthetic route, were found to have a remarkable effect on the performance of the sensors. Reduction of GO was achieved by immersing the modified electrodes into a stirred solution of NaBH4 for 10min at room temperature. This process was used alternatively of the time consuming and laborious process of hydrazine, and its effectiveness was confirmed by cyclic voltammetry and electrochemical impedance spectroscopy. Analytical utility of the sensors is demonstrated. [ABSTRACT FROM AUTHOR]