Table of Contents

Abstract: Linear scan voltammetry (LSV), differential pulse voltammetry (DPV) and voltammetry with adsorptive accumulation (AAV) at a glassy carbon paste electrode (GCPE) based on mixing glassy carbon spherical microparticles with an organic pasting liquid were used for the determination of trace amounts of carcinogenic 1-nitropyrene (1-NP) (the limit of determination around 2.10^-5 mol L^-1 for LSV and 2.10^-6 mol L^-1 for DPV) and 1-aminopyrene (1-AP) (the limit of determination around 3.10^-6 mol L^-1 for LSV, 1.10^-6 mol L^-1 for DPV and 1.10^-7 mol L^-1 for AAV) using a Britton-Robinson buffer – methanol mixture as a base electrolyte. The main advantage of this new type of electrode is its full compatibility with media containing a high amount of organic solvent (methanol, acetonitrile)

Abstract: Based upon the quasi-equilibrium approximation, the validity of p-n junction modelling, has been experimentally investigated under synchronous electrical and optical excitation of silicon photo-diodes. The devices had areas of 8.2 mm² and reverse bias saturation currents of the order of 10^-10 A. Their current-voltage (I-V) response was exploited experimentally both in the dark and under various illumination levels. The quoted values for the saturation current, the ideality factor, the series resistance and the reverse-bias photocurrent are investigated for the simulation of the I-V curves via the quasi-equilibrium model. In addition, the measured I-V data have been further analysed to estimate the produced photocurrent as a function of the applied bias (forward or reverse) under given illumination levels. Comparisons between the simulated curves and the experimental data allowed a detailed photocurrent modelling validation. The proposed approach could be useful towards studying other parameters of optically activated p-n junctions such as: the bias dependence of the minority carrier diffusion lengths and/or the generated rates of electron-hole pairs (EHP).

Abstract: The supermolecular interactions of single-stranded yeast DNA (ssDNA) and double-stranded DNA (dsDNA) with ferrocenium (Fc⁺) both in solution and at the electrode/solution interface were studied with UV spectroscopy and electrochemical method. The interaction of covalently immobilized dsDNA with Fc⁺ resulted in a change of the electrode behavior from diffusion-controlled to surface-controlled and an increase in the current response of Fc⁺ reduction, which has been used to develop a novel electrochemical yeast DNA sensor for hybridization recognition of immobilized yeast ssDNA to its complementary ssDNA (cDNA). The adsorption constants of Fc⁺ on ssDNA and dsDNA modified gold electrode surface were (3.38±0.04)×103 M^-1 and (2.02±0.02)×104 M-1, respectively, indicating a higher affinity of dsDNA to Fc⁺. UV spectra and the influence of ion strength showed that the interaction mode between Fc⁺ and dsDNA in solution might be a groove binding. The interaction between Fc⁺ and immobilized DNA was mainly an electrostatic model.