This paper reports on a facile method for synthesizing gold nanoparticles (AuNps) with diameter around 5 nm encapsulated with water-soluble polythiophene sulfonate poly[2-(3-thienyl) ethyloxy-4-butylsulfonate] sodium salt (PTS) and their physical-chemical characterization. The synthesis of hybrid materials of polythiophene derivatives and gold nanoparticles is a way to improve the polymer properties, mainly in application for chemical and optical sensing platforms. The AuNps were prepared by reducing gold salt with acid aqueous sodium citrate by the Turkvich method in the presence of PTS, and both PTS and citrate helped to stabilize the AuNps. The suspensions of AuNp: PTS presented good chemical and photostability for long period of storage. The nanoparticles encapsulated with the polymer presented smaller diameters than those obtained using only sodium citrate, according to scanning electron microscopy images. The AuNps obtained were used for fabrication LbL films with commercial chitosan, which were characterized by impedance spectroscopy measurements. The results showed that the charge transfer resistance values (Rct) decrease as the average diameter of the AuNps decreases and the proportion of PTS increases in the nanocomposite. Such increase of the nanocomposite conductivity, given by the low values of Rct, indicates that the novel film architecture developed is promising for chemical sensing applications. (C) 2016 Wiley Periodicals, Inc.