Melanin-Mediated Growth of Ag Nanostructures for Ultrasensitive SERS of l -Dopa

Hybrid interfaces based on melanin films and electrochemically deposited silver nanoparticles (Mel@Ag) are presented as effective platforms for ultrasensitive surface-enhanced Raman scattering (SERS). Natural melanin extracted from sepia pigment was processed into homogeneous thin films on indium tin oxide (ITO) via a controlled dip-coating approach, providing a chemically stable and redox-active interface. The presence of the melanin layer promotes an anodic shift in the Ag+ reduction potential and enables controlled nucleation and growth of silver nanostructures. The resulting Mel@Ag systems exhibit enhanced plasmonic response and superior SERS performance, with optimal activity achieved at low scan rates. Experimental results combined with electromagnetic simulations indicate that nanoparticle dimers play a dominant role in generating effective hotspots, particularly under 638 nm excitation, where a larger near-field enhancement volume is observed. The analytical capability of the platform is demonstrated through the detection of l-Dopa down to 10−11 M. The melanin layer likely contributes not only to control the nanostructure growth but also to analyte preconcentration through π−π interactions, favoring molecular localization at plasmonic hotspots. Notably, the system retains measurable SERS activity in complex biological media, demonstrating the persistence of the SERS response despite increasing matrix complexity. These results highlight the potential of melanin-mediated hybrid architectures as versatile SERS platforms for sensing applications in biologically relevant environments.