AuAg-Modified Porous Silicon Nanowires for Dual-Mode Interferometric and SERS-Based Bacterial Detection

In this study, a novel approach for simultaneous interferometric and surface-enhanced Raman spectroscopy (SERS) detection of bacteria utilizing porous silicon nanowires (pSi NWs) modified with silver and gold nanoparticles is reported. The pSi NWs were fabricated through gold-assisted chemical etching of p-type, single-crystal silicon wafers with a (100) crystallographic orientation and resistivity between 1 and 5 mΩ·cm. Following etching, the nanowires' surfaces were modified with silver, then gold nanoparticles by reduction from their respective salts in the presence of 5 M HF. This dual-mode sensing platform was tested with <i>Listeria innocua</i>, a nonpathogenic strain of <i>Listeria</i>, demonstrating significant interferometric fringe shifts after bacterial adsorption due to changes in the samples' effective optical thickness. This interferometric method achieved detection limits of <i>L. innocua</i> down to 6.4 × 10⁶ CFU/mL. Additionally, the plasmonic nanoparticle-modified nanowires exhibited strong SERS activity, enabling Raman spectral detection of adsorbed bacteria with a sensitivity limit of 3.2 × 10⁶ CFU/mL. This work demonstrates the potential of AuAg-modified pSi NWs as a versatile and highly sensitive dual-mode optical sensor for rapid bacterial detection, offering both real-time refractive index-based interferometric monitoring and molecularly specific SERS capabilities.