Influence of silver immersion time on the SERS activity of silver nanostructures on porous silicon templates for methylene blue detection

Abstract

This study optimizes the silver nanostructures templated on porous silicon (Ag/pSi) substrates through time-dependent immersion in a silver nitrate solution and investigates the surface-enhanced Raman spectroscopy (SERS) activity for the detection of Methylene Blue (MB). Porous silicon was fabricated via electrochemical etching of boron-doped silicon (100) at a fixed anodic current of 15mA, followed by immersion in a 0.01 M silver nitrate solution at varying dipping times (15s, 30s, 45s, and 60s). X-ray diffraction confirmed the systematic deposition of silver nanostructures, with peak intensities increasing proportionally to immersion duration. To demonstrate that the silver acts as the surface-enhancing material for Raman detection, MB was first dropped onto the bare porous silicon (pSi) template, where no detectable Raman signal was observed. Furthermore, SERS analysis shows that while silver deposition increases over time, the maximum Raman signal enhancement occurs at the 45-second duration. Beyond this threshold, nanoparticle coalescence leads to a reduction in electromagnetic hotspots. These results identify 45s as the optimal deposition time for achieving high-sensitivity molecular sensing.