Electrochemically Controlled Raman Response in Electropolymerized Polymethylene Blue–Gold Nanoparticle Films on Screen-Printed Carbon Electrodes

Hybrid electropolymerized films combining polymethylene blue (PMB) and gold nanoparticles (AuNPs) were prepared on screen-printed carbon electrodes (SPCEs) to investigate the electrochemical control of Raman response in redox-active hybrid interfaces. The resulting PMB@AuNP films provide a conductive and electroactive matrix that enables the coupling of electrochemical modulation with Raman spectroscopic readout. The electrochemical behavior of PMB@AuNP/SPCE was dependent on the applied potential, with negative potentials promoting changes in the optical response of methylene blue, evidenced by modulation of the background fluorescence associated with the reduction process. Film composition was systematically evaluated using oppositely charged redox probes, revealing that a PMB:AuNP ratio of 2:1 offers enhanced charge transport and balanced electrochemical response. Under these optimized conditions, the platform was applied to the electrochemical detection of paraquat in aqueous solution, achieving a limit of detection of 4.8 × 10–7 mol L–1. Spectroelectrochemical measurements further demonstrated that the Raman response is sensitive to the excitation wavelength, with enhanced signals observed under resonance conditions. Overall, these results demonstrate that electropolymerized PMB@AuNP films on SPCEs enable electrochemically controlled Raman response, highlighting their potential as integrated spectroelectrochemical interfaces for sensing applications.