Silver nanoparticles modified on cicada wings affect fluorescence and Raman signals based on electromagnetic and chemical enhancement mechanisms

The electromagnetic enhancement (EM) mechanism is one of the important theories that need to be mastered to study surface-enhanced fluorescence (SEF) and surface-enhanced Raman scattering (SERS). However, the charge transfer in the chemical enhancement (CM) mechanism has different effects on the two. The study developed a simple and environmentally friendly composite structural substrate by depositing silver (Ag) on the rough surface with regular columnar protuberances of bio-material cicada wings (CW) using magnetron sputtering technology. The formation of Ag nano-islands enhanced the fluorescence and Raman signals of rhodamine 6G (R6G), while the addition of silver nanoparticles (AgNPs) quenched the fluorescence. To explore the magical phenomenon, the electromagnetic field distribution on the surface of the substrate was simulated through three-dimensional finite difference time domain (3D-FDTD), which verified the experimental results of SEF and SERS. The results calculated by Gaussian16 with Density Functional Theory (DFT) and time-dependent density functional theory (TDDFT) explained the effect of adding AgNPs on the surface of the substrate on the fluorescence intensity. The work not only contributes experimental data and theoretical results to the EM mechanism and CM mechanism in enhanced spectra, but also provides ideas for preparing new SEF and SERS substrates.