Enhanced optoelectronic properties of RNA–poly(o-methoxyaniline) hybrid containing monodispersed Aunanoparticles

Abstract

In situ, gold nanoparticles are produced in poly(o-methoxy aniline) (POMA)–RNA (R) hybrids; POMA (P) acting both as reductant and stabilizer. The POMA (emeraldine base, EB) is oxidized into a mixture of POMA (emeraldine salt, ES) and POMA (pernigraniline base, PB) in the course of reaction as evident from FTIR and UV-vis spectra. The Au nanoparticles are of uniform size (diameter ∼ 14 nm) and the density of Au nanoparticles increases with increase in POMA (EB) concentration showing a maximum of 150 × 10¹⁰ particles per square centimetre in PRAu31 (the number indicates respective weight ratio). The electron diffraction pattern indicates the polycrystalline nature of the Au nanoparticles and CD spectra suggest a small conformational distortion of the A helix of RNA towards the B helix in the nanobiocomposite. The FTIR spectra indicate the presence of H-bonding, π–π and ionic interactions between POMA (ES) and RNA, and the Au nanoparticles are stabilized by complexation through nitrogen atoms of POMA (PB). The π band to polaron band transition peak of POMA shows a gradual red shift with aging time and the shift is greater in the case of POMA–RNA–Au nanobiocomposites than that of the POMA–RNA hybrid. The larger shift in the PRAu nanocomposites compared to the POMA–RNA hybrid is attributed to the more uncoiled state of POMA for stabilizing Au nanoparticles. The POMA–Au system generates new photoluminescence properties when excited at 500 nm and PL intensity increases abruptly with the addition of RNA in the hybrid. The excitation of plasmon electrons and the stabilization of excitons in the conjugated chain of POMA is attributed to the new PL property and its enhancement with addition of RNA is due to the increased conjugation length of POMA on the RNA surface. PRAu13 shows rectification property, while the other compositions do not exhibit such behavior. The rectification is explained from the band energy diagram, and its absence in PRAu11 and PRAu31 hybrids is attributed to the increased concentrations of Au and POMA causing a better conducting composite material.