Conducting, crystalline and electroactive polyaniline-Au nanocomposites through combined acid and oxidative doping pathways for biosensing applications: Detection of dopamine

Abstract

Abstract Acid and oxidative doping pathways have been employed in synergy to synthesize polyaniline-gold (PANI-Au) nanocomposites using appropriate reagents and optimized synthesis procedures. Sulphuric and p-toluene sulphonic acids (pTSA) were used as protonic acid dopants and chloroauric acid as an oxidative dopant. The acid dopants enhanced the conductivity of polyaniline (PANI) while the oxidative dopant improved the crystallinity by oxidising the benzenoid units of PANI with a concomitant reduction of Au (+3) to metallic gold at the imine sites. The conducting nature of the PANI and PANI-Au nanocomposites was compared using UV-Vis, FTIR spectroscopy and conductivity data. The crystallinity of the nanocomposites was revealed through X-ray diffraction patterns whereas transmission electron microscopy analysis showed that the size of the gold nanoparticle in the PANI matrix lies between 10 and 80\xa0nm. Scanning electron microscopy images revealed the layered structure of PANI in pTSA compared to the compact structure in sulphuric acid medium. Thus pTSA separated inter and intra chains of PANI resulting in layered and ordered morphology. The electrochemical studies revealed that the PANI-Au modified electrode surfaces were electroactive near neutral pH, suitable for biosensing application. The fabricated electrode detected dopamine with good sensitivity and excellent selectivity amidst interferences, ascorbic and uric acid.