Optoelectronic properties of RNA–polyaniline–dendritic gold nanobiocomposite

The in situ reduction of Au+++ by aniline in the presence of RNA produces dendritic Au nanoparticles (AuNP) with the concomitant formation of doped polyaniline (PANI). FT-IR spectra indicate that the dendritic AuNPs are stabilized from the complexation of nitrogen atoms of quinonoid structure of PANI with the adsorbed Au+++ on it. CD spectrum indicates a small distortion of RNA ‘A’ helix toward ‘B’ helix. RNA–PANI–Au nanocomposite shows emission peak at 408 nm with an additional peak at 579 nm for the Forster resonance energy transfer (FRET) of PANI excitons to surface plasmon band of Au nanocrystals. The dendritic RNA–PANI–Au nanocomposite has three orders higher dc-conductivity compared to the spherical PANI–Au composite. Impedance data suggest that the system behaves as an equivalent parallel resistance–capacitance (R–C) circuit. The frequency dependency of ac-conductivity indicates three regions of conduction: at low frequency predominantly intrachain conduction by polarons of doped PANI, at medium frequency hopping of polarons through RNA and AuNP along with the intra-chain conduction and at very high frequency the conductivity is predominantly interchain due to localized hopping.