Optical and electronic properties of polyaniline sulfonic acid-ribonucleic acid-gold nanobiocomposites

Abstract

Finely fibrillar polyaniline sulfonic acid (PSA)/ribonucleic acid (RNA) hybrids are developed by wrapping PSA with RNA from a mixture of aqueous PSA (P) and RNA (R) solutions of different compositions. FTIR spectra suggest H-bonding and π-π interactions in the hybrids and dedoping of self doped PSA during hybrid formation. UV-vis spectra exhibit a blue shift of the π-band to polaron band transition of PSA from 870 to 581 nm due to dedoping. The PR hybrids show enhanced PL-properties when excited at 540 nm relative to PSA which also exhibits rectification behavior in current (I)-voltage (V) curves. Gold nanoparticles (Au NPs) grown on these PR hybrids by the reduction of Au³⁺ by PSA show different morphologies with varying composition. FTIR spectra of the nanobiocomposites indicate that Au NPs are stabilized by the co-ordination of the nitrogen atoms of -N=Q=N- bonds of PSA (Q = quinonoid ring). The intensity of the Au plasmon band gradually decreases with time but the PL-intensities of the PAu/PRAu nanocomposites increase with time. The PL-intensity of the nanocomposites is higher than that of PSA and PR hybrids. The DC-conductivity of the PR hybrids increases by an order of magnitude on addition of Au NPs. I-V curves of the nanobiocomposites show negative differential resistance (NDR) in PSA rich systems with a stable NDR ratio of 7 in the PRAu21 and PRAull hybrids. Possible reasons from the accumulation of charges on the Au NPs and its stabilization through the π-clouds of RNA bases are discussed. The PRAu11 system also exhibits rectification properties with a rectification ratio of 14.