In situ surface-enhanced Raman scattering investigation of poly(5-amino-1,4-naphthoquinone) using roughened electrodes and metal colloids

Abstract

Electropolymerization of 5-amino-1,4-naphthoquinone on electrochemically roughened gold electrode has been performed by anodic oxidation of the monomer in CH3CN+0.1M LiClO4 electrolytic medium. The cyclic voltammograms recorded during the first stages of electropolymerization clearly demonstrate the competition between the oxidation reactions of the monomer and the working electrode. Thanks to the surface asperities of the roughened electrode and to gold particles embedded within the inner layers of the polymer, the Raman analyses with red laser line led to the observation of surface-enhanced Raman scattering effect. The in situ SERS spectra of poly(5-amino-1,4-naphthoquinone) obtained during the gradual variation of the electrode potential between the reduced and the oxidized states in both directions in CH3CN+LiClO4 medium confirmed the electroactivity and electrochemical stability of the polymer during the doping-undoping process, as well as the reversibility of the transition between the oxidized (CO) and reduced (CO−⋯Li+) forms of the quinone groups. Moreover, SERS analyses were also carried out using metal colloids. In this case, despite the very low polymer concentration (traces) and the mild experimental conditions (weak laser power) used in these experiments, a large amplification of the Raman signal took place. Thanks to the suspension of silver or gold particles, the polymer displays a SERS effect, which greatly improves the signal-to-noise ratio of the Raman spectra, thus allowing to perform a much better vibrational analysis and to determine the orientation and the fixation mode of the polymer on the metal surface.