Femtosecond laser fabrication of silver plasmonic structures for application as single particle SERS detectors

This work demonstrates the feasibility of fabricating silver nanoparticles (NPs) into sub-micron and micron-sized core-satellite structures by exposure to femtosecond laser radiation. We find that the size and shape of these structures can be tailored by adjusting laser fluence (1.8–10.5 J cm−2) and irradiation time (20–60 min), along with the concentration of NPs in aqueous solution (0.01–0.05 mM). Raman measurements of adenine molecules adsorbed on these sub-micron substrates indicate that core-satellite structures having complex shapes are effective as sensitive surface enhanced Raman spectroscopy (SERS) substrates. The sensitivity is such that these structures are potentially useful as single particle SERS substrates for bio-sensing. Finite difference time domain (FDTD) simulation results indicate that these structures can be generated by the joining of NPs in response to localized surface plasmon induced hotspots.