Polyanilines-Functionalized Gold Nanoparticles on Screen-Printed Electrodes: A Redox-Active SERS Probe and Sensitive Platform for EC-SERS Analysis

In this work, a new platform for electrochemical surface-enhanced Raman spectroscopy analysis (EC-SERS) based on polyaniline-functionalized gold nanoparticles (PANI@AuNPs) was proposed. The aim of the study was to develop a stable, redox-active nanosensor with a wide range of potentials, enabling the monitoring of oxidation and reduction processes. PANI@AuNPs were obtained by modifying Au nanoparticles synthesized by the Turkevich method with a thin layer of polyaniline (PANI) and then characterized using UV–vis, DLS, SEM, and TEM techniques. Electrochemical studies showed the activity of PANI@AuNPs in a wide pH range (3–8), which is associated with interactions between charged citrate groups and PANI chains. Using EC-SERS, characteristic Raman bands corresponding to PANI oxidation states were identified, which served as redox markers. Three band intensity ratio indices (1570/1600, 1252/1177, and 1455/1412 cm–1) were proposed, enabling measurements in the potential range of 700 mV, which is an improvement over quinone-based nanosensors that achieve a range of around 300 mV (making them suitable for oxidative stress studies). The demonstration of H2O2 detection showed that the addition of horseradish peroxidase (HRP) enzyme lowers the detection limit from 10–4 to 10–8 M, confirming the system’s effectiveness in the analysis of reactive oxygen species. The results indicate the potential of PANI@AuNPs in biological applications. The potential application of the platform is the dynamic monitoring of intracellular redox potential.