Templated silver nanoparticle deposition on laser-induced periodic surface structures for SERS sensing

Organized assemblies of metal nanoparticles exhibit unique optical properties and can be used as platforms for surface-enhanced Raman scattering (SERS) to detect small amounts of analyte molecules. In this work, we demonstrate that using Yb:KGW femtosecond laser structuring of silicon wafer we can modify surface properties by creating laser-induced quasi periodic surface structures (LIPSS) of 850 +/- 43 nm periodicity. We show that silicon with LIPSS is a suitable surface for direct nanoparticle deposition because of its superhydrophilic properties and the nanoparticle density affects the density of the hot spots contributing in the Raman enhancement. We have analyzed the influence of the silver nanoparticle deposition on the structured silicon surface conditions on their density and coverage. 101 +/- 8 nm size silver nanoparticles were deposited by two methods, namely drop casting colloidal solution at three different temperatures (4 degrees C, 21 degrees C, 35 degrees C) and their SERS enhancements were compared with the monolayers deposited by liquid-liquid interface. It was found that monolayer deposition on a structured surface was the best approach in the sense of even silver nanoparticles coverage which exhibited best SERS performance reaching a limit of detection of 10- 7 M for 2-naphthalenethiol. The obtained LoD is comparable with that of commercial substrates available in the market.