G-rich oligodeoxynucleotides (ODNs) have great medical and nanotechnological potential, because they can self-assemble into G-quadruplexes and higher-order nanostructures. The folding properties of d(G)10, d(TG9) and d(TG8T) ODNs were studied using atomic force microscopy (AFM) and voltammetry at carbon electrodes. Single-stranded ODNs, in Na(+) containing solutions and for short incubation times, were detected using AFM as network films and polymeric structures and using voltammetry by the occurrence of only the guanine oxidation peak. G-quadruplexes, in Na(+) containing solutions and long incubation times, or in K(+) containing solutions, were detected using AFM as spherical aggregates and using voltammetry by the decrease of the guanine oxidation peak and the occurrence of the G-quartet oxidation peak. Concerning the self-assembling into higher-order nanostructures, d(G)10 was the only sequence forming G-nanowires observed using AFM, d(TG9) formed short G-based super-structures that adsorbed as rod-like shape aggregates, and d(TG8T) formed no nanostructures, due to the presence of thymine residues at both 5' and 3' ends.

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Microcystin-LR (MC-LR) and nodularin (NOD), two potent cyanotoxins with strong hepatotoxic, genotoxic and carcinogenic potential have been associated with the induction of deoxyribonucleic acid (DNA) damage in vitro and in vivo. Electrochemical studies were performed to understand the DNA interaction mechanisms with MC-LR and NOD using a dsDNA-electrochemical biosensor and incubated solutions. The decrease of the dsDNA oxidation peaks with increasing incubation time due to aggregation of DNA strands and the liberation of adenine free residues, causing the occurrence of DNA abasic sites, was observed, which may introduce mutations in the dsDNA during the replication process.

Sonoelectrochemical degradation (US-EC), a relatively new AOPs, is a technique that combined sonication (US) and electrolysis (EC) without the need for additional chemicals for the procedure. Microcystin-LR (MC-LR), as the most toxic and most widespread algal toxin, are threat to human health. Until now US-EC technique have never been applied to MC-LR decomposition. The aim of this paper is to study the effect of MC-LR degradation of US-EC, optimize the sonochemical and electrochemical parameters involved in MC-LR decomposition. US-EC degradation of MC-LR was better than US or EC alone in terms of time and degradation efficiency. The degradation rate of MC-LR was up to 93% applying US (20 kHz ,15 W) to the EC (6 mA cm-2) for 5min, and the residual concentration of MC-LR in the water was less than 1µg L-1 (the limits set by WHO). With processing time is extended to 10 minutes, the degradation rate was reached 99%.

The electrochemical behaviour of Nodularin (NOD), a hepatotoxic cyclic pentapeptide, was studied at a glassy carbon electrode. NOD electrochemical oxidation is an irreversible, pH-independent process, involving the transfer of one electron. Upon incubation in different pH electrolytes, chemical degradation of NOD was electrochemically detected by the appearance of a new oxidation peak. The chemically degraded NOD (cdNOD), undergoes an irreversible, pH-dependent oxidation, and its redox products are reversibly oxidised. The charge transfer properties of cdNOD as well as of its redox metabolites were investigated. Mechanisms for NOD oxidation, NOD chemical degradation and oxidation of cdNOD and its metabolites were proposed.