Radovan Metelka

Bismuth-film-plated carbon paste electrodes

Abstract In this preliminary note, carbon paste electrodes (CPEs) plated with a bismuth film are presented. The bismuth film can be generated onto the carbon paste surface either from an external plating solution or in situ; the latter being performed in two ways: (i) as a spike of the Bi 3+ ions to the solution or (ii) via modifying the carbon paste with solid bismuth oxide (5% m/m). As shown on selected examples, bismuth-film-plated CPEs exhibit a good performance in voltammetric stripping analysis of some heavy metals such as Pb, Cd, and Zn.

Magnetic beads-based electrochemical immunosensor for monitoring allergenic food proteins.

Screen-printed platinum electrodes as transducer and magnetic beads as solid phase were combined to develop a particle-based electrochemical immunosensor for monitoring the serious food allergen ovalbumin. The standard arrangement of enzyme-linked immunosorbent assay became the basis for designing the immunosensor. A sandwich-type immunocomplex was formed between magnetic particles functionalized with specific anti-ovalbumin immunoglobulin G and captured ovalbumin molecules, and secondary anti-ovalbumin antibodies conjugated with the enzyme horseradish peroxidase were subsequently added as label tag. The electrochemical signal proportional to the enzymatic reaction of horseradish peroxidase during the reduction of hydrogen peroxide with thionine as electron mediator was measured by linear sweep voltammetry. The newly established method of ovalbumin detection exhibits high sensitivity suitable for quantification in the range of 11 to 222nM and a detection limit of 5nM. Magnetic beads-based assay format using external magnets for rapid and simple separation has been proven to be an excellent basis for electrochemical detection and quantification of food allergens in highly complex sample matrices.

Determination of arsenate and organic arsenic via potentiometric titration of its heteropoly anions

Determination of arsenate based on its conversion to molybdoarsenate heteropoly anions followed by potentiometric titration is described. The titration is realized on the ion-pairing principle using cetylpyridinium chloride (or an analogous titrant containing a lipophilic cation), and is monitored by a carbon paste electrode, although other liquid-polymeric membrane-based electrodes can also be used. Calibration plots of the titrant end-point consumption versus concentration of arsenic were constructed and used to evaluate the content of arsenic in aqueous samples. The method could be applied in the analyses of samples with quite low arsenic content (amounts approximately 10 mug As in 50 cm(3) could be titrated). Organic arsenic was determined analogously after the Schöniger combustion of the sample and conversion of its arsenic to arsenate.

Immunomagnetic sulfonated hypercrosslinked polystyrene microspheres for electrochemical detection of proteins

Poly(styrene-co-divinylbenzene) microspheres of narrow size distribution were prepared by (2-hydroxypropyl)cellulose-stabilized dispersion copolymerization of styrene and divinylbenzene in a 2-methoxyethanol/ethanol mixture under continuous addition of divinylbenzene. The copolymerization was initiated with dibenzoyl peroxide. The obtained microspheres were chloromethylated using several chloromethylation agents and then hypercrosslinked. Their porous structure was analyzed by nitrogen adsorption and mercury porosimetry. Superparamagnetic iron oxide nanoparticles were precipitated within the pores of microspheres from Fe(II) and Fe(III) chloride solution. The Fe content in the microspheres was determined by carbon analysis, atomic absorption spectroscopy and thermogravimetric analysis. Magnetic properties of the microspheres were characterized by magnetization curves and the temperature dependence of magnetic susceptibility. Finally, sulfo groups were introduced into the microspheres to prepare an immunomagnetic electrochemical biosensor for protein detection with ovalbumin as a model substance.

Voltammetric behaviour and quantitative determination of pesticide iminoctadine

Iminoctadine (IOD) was determined in spiked river water samples by square wave voltammetry (SWV) using a cyclic renewable silver amalgam film electrode (Hg(Ag)FE). It was found that the compound can act as an electrocatalyst. In Britton–Robinson buffer at pH 6.5 a signal connected with the catalytic hydrogen evolution reaction was detected at −1.8 V versus Ag/AgCl. Validation of the method was carried out. The LOD and LOQ have been estimated to be 2.6 × 10−9 mol L−1 and 8.5 × 10−9 mol L−1, respectively.

Determination of vitamin E in margarines and edible oils using square wave anodic stripping voltammetry with a glassy carbon paste electrode

A new electroanalytical method for determination of vitamin E in the form of the total content of tocopherols present in margarines and edible oils has been developed. The method is based on extraction of these biologically active compounds into silicone oil, acting as lipophilic binder of glassy carbon paste electrode, with subsequent electrochemical detection by square wave anodic stripping voltammetry (SWASV) in 0.1M HNO3. The values of vitamin E contents were expressed as mass equivalent of α-tocopherol known as the most active form of this lipophilic vitamin. The linear ranges for α-tocopherol determination were 5×10-7-4×10-5 and 5×10-8-1×10-5molL-1 with the detection limits of 1×10-7 and 3.3×10-9molL-1 for 5 and 15min accumulation, respectively. The results have shown that SWASV with extraction step is very sensitive method for the determination of vitamin E, being comparable to reversed-phase high performance liquid chromatography chosen as reference method.

A simple and easy way to enhance sensitivity of Sn(IV) on bismuth film electrodes with the use of a mediator

For the first time an in situ-plated bismuth film electrode prepared with the use of a reversibly deposited mediator (Zn) was applied to anodic stripping voltammetry of the metal ions. This simple and easy way of the electrode surface modification by metal films was suggested to increase the voltammetric signal of Sn(IV) and, consequently, to improve the sensitivity and tin detection limit. The structural and chemical information about the bismuth films plated with and without the use of the mediator were derived from AFM and XPS data analysis.Graphical abstract

Verification of antibody labelling efficiency as an important step in ELISA/QLISA development

A simple and effective method for validation of antibody labelling procedure as well as for optimal conjugate dilution assessment based on electrochemical detection is presented. Enzyme alkaline phosphatase and core-shell CdSe/ZnS quantum dots are used as sensitive tag exploitable as detection tool of antibody-antigen complex in magnetic microbead-based immunoassays. Square-wave voltammetry for detection of the electroactive product that is induced by conversion of appropriate substrate by alkaline phosphatase and square-wave anodic-stripping voltammetry for signal of Cd in case of quantum dots, respectively, was elected. Anti-Apo E IgG antibodies were selected as model molecules for method optimizations.Graphical abstract

Improvement of enzyme carbon paste-based biosensor using carbon nanotubes for determination of water-soluble analogue of vitamin E

The catalytic oxidation of a synthetic water-soluble analogue of vitamin E (α-tocopherol, Trolox) by tyrosinase enzyme in the presence of molecular oxygen was studied using electrochemical techniques. This specific enzymatic reaction was exploited for the preparation of a biosensor based on the amperometric reduction of the electroactive product (α-tocoquinone) formed. An electroactive surface of the transducers used was covered with a thin conductive layer of Nafion containing tyrosinase. Significant progress in sensitivity towards polyphenolic compounds such as Trolox was achieved at CPE with carbon nanotubes immobilised on its surface (CPE/CNTs) as electric transducers. The biosensor so developed can be used for the direct determination of total phenolic content (TPC). This important nutrition value can be expressed as the mass equivalent of Trolox, i.e. Trolox equivalent antioxidant capacity (TEAC), which could be used as an alternative to the evaluations currently used based on spectrophotometric methods such as total radical-trapping antioxidant parameter (TRAP), ferric reducing-antioxidant power (FRAP) or 1,1-diphenyl-2-picrylhydrazyl spectrometric assay (DPPH). The effects of the enzyme amount in the Nafion layer (3.0 µg), the influence of the nanoparticles present, the optimal pH value suitable for enzymatic activity (7.0), and the kinetics of enzymatic and electrochemical reactions were studied using cyclic voltammetry (CV). The determination of optimal conditions for amperometry in batch configuration (working potential, speed of stirring, volume of sample, calibration curve, etc.) was not a target of this electrochemical study.

Application of screen-printed carbon electrode modified with lead in stripping analysis of Cd(II)

Abstract In the work presented, a lead film electrode was prepared in situ on a screen-printed carbon support using a reversibly deposited mediator (Zn) and applied to the determination of Cd(II) by anodic stripping voltammetry. The electrochemical method for lead film formation is based on a co-deposition of a metal of interest (Pb), with a reversibly deposited zinc mediator, followed by oxidation of zinc, with additional deposition of lead at the appropriate potential. It serves to increase the density of lead particles, promoting lead film growth, and consequently helps to improve the electrochemical properties of the electrode. This was confirmed by microscopic and voltammetric studies. The obtained detection limit of Cd(II) is equal to 6.6 × 10−9 mol L−1 (−1.6 V for 180 s and then −0.95 V for 5 s). The presented procedure was successfully applied to cadmium determination in Bystrzyca River water samples.