Marian Vojs

Doping Level of Boron-Doped Diamond Electrodes Controls the Grafting Density of Functional Groups for DNA Assays

The impact of different doping levels of boron-doped diamond on the surface functionalization was investigated by means of electrochemical reduction of aryldiazonium salts. The grafting efficiency of 4-nitrophenyl groups increased with the boron levels (B/C ratio from 0 to 20,000 ppm). Controlled grafting of nitrophenyldiazonium was used to adjust the amount of immobilized single-stranded DNA strands at the surface and further on the hybridization yield in dependence on the boron doping level. The grafted nitro functions were electrochemically reduced to the amine moieties. Subsequent functionalization with a succinic acid introduced carboxyl groups for subsequent binding of an amino-terminated DNA probe. DNA hybridization significantly depends on the probe density which is in turn dependent on the boron doping level. The proposed approach opens new insights for the design and control of doped diamond surface functionalization for the construction of DNA hybridization assays.

Self-assembled sensor based on boron-doped diamond and its application in voltammetric analysis of picloram

A self-assembled sensor based on a boron-doped diamond was investigated as a sensitive tool for voltammetric analysis of a member of a pyridine herbicide family - picloram. A cyclic voltammetry and a differential pulse voltammetry were applied for investigation of the voltammetric behaviour and quantification of this herbicide. Picloram yielded one well-developed irreversible oxidation signal at a very positive potential about +1.5 V vs. Ag/AgCl/3 mol L−1 KCl electrode in an acidic medium and 1 mol L−1 H2SO4 was chosen as a suitable supporting electrolyte. Operating parameters of differential pulse voltammetry were optimized and the proposed voltammetric method provided a high repeatability (a relative standard deviation of 20 repeated measurements at a concentration level of picloram of 50 µmol L−1 equaled to 2.58%), a linear concentration range from 2.5 to 90.9 µmol L−1 and a low limit of detection (LD = 1.64 µmol L−1). Practical usefulness of the ‘environmentally-green’ electrochemical sensor was verified by an analysis of spiked water samples with satisfactory recoveries.

Raman Spectroscopy of Amorphous Carbon Prepared by Pulsed Arc Discharge in Various Gas Mixtures

To meet various application requirements, it is important to enable an improvement of a-C structure and properties, such as hardness, adhesion, and wear resistance. In this study, we used the Raman spectroscopy to investigate the a-C thin films structure dependence on the different deposition parameters. The effect of nitrogen, argon, and hydrogen gas flow rate was analyzed to determine the influence on the film properties. The change in the gas type, combination, and flow had a significant influence on the D and G bands of the a-C Raman spectra. The addition of N2 into the chamber promoted the sp2 creation, while with adding hydrogen the layer contained more sp3 bonds. The depositions of a-C thin films were carried out in pulsed arc discharge vacuum installation. Micro-Raman measurements of the deposited materials were performed using an ISA Dilor-Jobin Yvon-Spex Labram confocal system with 632.8 nm radiation from a He-Ne laser using a back-scattering geometry.

Simple and Rapid Quantification of Folic Acid in Pharmaceutical Tablets using a Cathodically Pretreated Highly Boron-doped Polycrystalline Diamond Electrode

ABSTRACT A simple, rapid, and sensitive electroanalytical method for the direct quantification of folic acid was developed using square-wave voltammetry with a cathodically pretreated highly boron-doped polycrystalline diamond electrode. The morphology and structure of this electrode were investigated by scanning electron microscopy and Raman spectroscopy. The electrochemical behavior of folic acid was studied by cyclic voltammetry and an irreversible oxidation peak was observed at +0.78 volt vs. Ag/AgCl in Britton-Robinson buffer at pH 5. Using optimized square-wave voltammetric parameter values, the response of folic acid was linear from 0.1 to 167 micromolar with a limit of detection of 30 nanomolar with good repeatability. The influence of some interfering compounds was also evaluated. The method was successfully applied to the quantification of folic acid in pharmaceutical tablets. Considering the importance of the analyte upon human health, the boron-doped diamond electrode may be employed as an effective alternative electroanalytical approach.

Diamond icosahedron on a TiN-coated steel substrate

Diamond layers have been deposited by hot filament chemical vapour deposition (HF CVD) on TiN-coated steel substrates. After deposition, we could observe separate, well-developed diamond icosahedrons and decahedrons on the surface. We have found that a lower content of methane in hydrogen supports their growth, this being a result of multifold twinning. The quality of diamond layers has been evaluated by Raman spectroscopy and scanning electron microscopy.

Electroanalytical application of a boron-doped diamond electrode for sensitive voltammetric determination of theophylline in pharmaceutical dosages and human urine

In this paper, a novel voltammetric method for the determination of 1,3-dimethylxanthine alkaloid theophylline is elaborated using differential pulse (DPV) and square-wave voltammetric (SWV) modes on a boron-doped diamond electrode. Direct oxidation of the analyte at very positive potentials was observed by cyclic voltammetry, as evidenced by the presence of a well-shaped irreversible peak at +1.63 V (vs. Ag/AgCl electrode) in 1 mol L−1 sulphuric acid. After optimization of experimental conditions, the current response of theophylline was proportionally linear from 2 to 380 μmol L−1 using both pulse techniques. The developed electroanalytical method yielded low detection limits of 0.91 and 1.45 μmol L−1 associated with good intra-day repeatability (relative standard deviation of 3.2 and 2.5%) using DPV and SWV, respectively. The influence of some possible interferents was also evaluated. The practical feasibility of the proposed methodology was tested in the analysis of pharmaceutical dosages and human urine samples and good recovery values were accomplished (93.2–102.5%). The results of analysis of pharmaceuticals were also in close agreement at a 95% confidence level with those obtained using the titration (reference) method. Taking these attributes into consideration, the proposed sensor may be employed as a simple and effective analytical tool in drug control analysis and analysis of biological samples as well as a useful alternative to previously utilized modified electrodes in this field.

The doping level of boron-doped diamond electrodes affects the voltammetric sensing of uric acid

In this work, the electrochemical oxidation and subsequent determination of uric acid was investigated using boron-doped diamond electrodes with various B/C ratios (0–2000 ppm). The cyclic voltammetric study showed one irreversible oxidation peak at +(1.1–1.25) V (vs. Ag/AgCl/3 M KCl) in the presence of Britton–Robinson buffer (pH 2.25) depending on the boron content. Employing differential pulse voltammetry using the 2000 ppm boron-doped diamond electrode the acquired analytical parameters were as follows: a limit of detection of 7.7 μM, a limit of quantification of 26 μM and intra-day repeatability (relative standard deviation of 2.9% for n = 15). After performing an interference study, the method was applied to the determination of uric acid in biological samples (human urine). The uric acid concentrations determined in the urine samples were compared with the reference values stated in the literature. The proposed methodology using boron-doped diamond electrodes could find applications in uric acid sensing within clinical, pharmaceutical and environmental analysis.

Influence of Diamond CVD Growth Conditions and Interlayer Material on Diamond/GaN Interface

In this study we present the diamond deposition on AlGaN/GaN substrates focusing on the quality of the diamond/GaN interface. The growth of diamond films was performed using microwave chemical vapour deposition system in different gas mixtures: standard CH4/H2 (at low and high ratio of CH4 to H2) and addition of CO2 to CH4/H2 gas chemistry. The diamond films were grown directly on GaN films either without or with thin interlayer. As interlayer, 100 nm thick Si3N4 was used. Surprisingly, in the case of standard CH4/H2 gas mixture, no diamond film was observed on the GaN with SiN interlayer, while adding of CO2 resulted in diamond film formation of both samples with and without SiN interlayer. Moreover, adding of CO2 led to higher growth rate. The morphology of diamond films and the quality of the diamond/GaN interface was investigated from the cross-section images by scanning electron microscopy and the chemical character (i.e. sp3 versus sp2 carbon bonds) was measured by Raman spectroscopy.

Properties of amorphous carbon layers for bio-tribological applications

This paper analyses the influence of composition, structure and adhesion of amorphous coatings with high wear resistance, low friction coefficient and good adhesion to coated CrCoMo material for parts of implants. By different deposition techniques, different mechanical and tribological properties were obtained. This work reviews amorphous carbon (a-C) films deposited by magnetron sputtering and diamond-like carbon (DLC) films grown by glow arc discharge technology on CrCoMo substrates. Films were investigated under static load under dry conditions (nanohardness, elastic module), and also with dynamic load (coefficient of friction, wear resistance). The following topics were investigated: surfaces and subsurface properties of a-C films, namely adhesion in connection with different techniques, different film properties in dependence on various technology conditions.

Rapid electrochemical platform for nicotine sensing in cigarettes and chewing gums

Abstract A novel protocol for the simple and rapid determination of nicotine using square-wave voltammetry at boron-doped diamond electrode was developed. The effect of pH of supporting electrolyte, scan rate and square-wave voltammetric parameters was examined. Behavior study revealed that nicotine provided two irreversible oxidation peaks, the first one well-shaped at +1.14 V and the second one poorly-defined at +1.61 V vs. Ag/AgCl electrode in the presence of phosphate buffer (pH 9.0). Under optimal experimental conditions (modulation amplitude of 40 mV, frequency of 50 Hz and scan rate of 0.225 V · s-1), the current response of nicotine was proportionally linear in the concentration range from 9.9 × 10-6 to 1.7 × 10-4 mol · L-1 (R2 = 0.996) with the detection limit of 6.1 × 10-6 mol · L-1 (0.989 mg · L-1) and the relative standard deviation of 8.8 % (number of measurements n = 10, 5.7 × 10-5 mol · L-1 nicotine). The proposed procedure was applied to the quantification of nicotine in cigarettes and chewing gums with the determined values in good agreement with those declared by producer. In this respect, the developed protocol could represent an effective and rapid alternative to chemically modified electrodes in analysis of alkaloids.