Electrochemical, microgravimetric and AFM studies of polythionine films: Application as new support for the immobilisation of nucleotides

The experimental conditions for the thionine potentiodynamic electropolymerisation in acidic media are optimised in order to achieve polythionine (PTN) modified electrodes with high stability and reproducible redox behaviour in acidic and biological compatible media. The data obtained by cyclic voltammetry and electrochemical quartz crystal microbalance (EQCM) show that under the selected conditions, polythionine films growth, presents a non-linear relation between mass and electroactivity which suggests structural changes during electropolymerisation, that are corroborated by atomic force microscopy (AFM). The pH effect in the redox switching of PTN films is studied in solutions with pH from 1.3 to 12 where two processes with different dependence on protons occurs in the interval from 5.5 to 9, indicating a complex behaviour. PTN redox conversion in acidic media is film thickness sensitive and a non-permselective behaviour is found in acidic and neutral media, being the mass change dependent on the electrolyte nature. The presence of free amino functions in the polymer structure enable the nucleotide immobilisation by adsorption and covalent attachment, which was simultaneously monitored by EQCM and open circuit potential. The nucleotidic phosphate groups reactivity is enhanced by adding coupling agents leading to an higher amount of mass immobilisation.