Polythiophene-g-poly(dimethylaminoethyl methacrylate) stabilized Au nanoparticles and its morphology tuning by RNA with variation of electronic properties

Abstract

The reducing ability of polythiophene-g-poly(dimethylaminoethyl methacrylate) (P) is used to produce Au nanoparticles (NPs), both in pure P and in different P–RNA (R) hybrids. The Au NPs have different morphologies, depending on the composition of P and R in the PRAu composites. The EDXS spectrum indicates the presence of RNA, P, and Au NPs in the composite. The CD spectra indicate a small distortion in the RNA conformation from A helix towards B helix and the FTIR data indicate the existence of π–π and ionic interactions between P and RNA. The Au plasmon band of the PAu composite shows a gradual red shift with increasing RNA concentration and the photoluminescence (PL) intensity of P decreases in the PAu composites. With increasing RNA concentration in the composite, there is more PL-quenching, and the quenching capacity of RNA is higher than that of DNA (D) and bovine serum albumin (BSA, B). The dc-conductivity of the PAu system is ∼6 times higher than that of P and it increases in the PRAu composites by 1–3 orders of magnitude depending on its composition. In the current–voltage (I–V) curve the PR13 hybrid exhibits rectification properties while the PAu nanocomposite exhibits an interesting feature of symmetric negative differential resistance (NDR). The PRAu31 composite (numbers indicate wt ratio of P and R) shows a small degree of NDR behavior, but the PRAu11 and PRAu13 systems do not show such a property. The rectification and NDR properties of the composites are discussed from the band diagram and the density of the state model, respectively.