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 Listeria innocua, a nonpathogenic strain of Listeria, demonstrating significant interferometric fringe shifts after bacterial adsorption due to changes in the samples' effective optical thickness. This interferometric method achieved detection limits of L. innocua 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.