Gold Nanoparticles/Porous Silicon Photonic Crystal with Tunable Bandgap for Wavelength-Matching, Ultrasensitive, and Background-Free Surface-Enhanced Raman Scattering Bioanalysis

Surface-enhanced Raman scattering (SERS) chips based on porous silicon photonic crystals (PSi PhCs) exhibit excellent optical modulation capability, enabling reamplify Raman signals. However, challenges remain in precisely tuning the bandgap to specific SERS laser wavelengths and constructing high-reflectivity microcavities capable of nanoparticle loading without compromising modulation performance. Here, we propose an effective strategy combining periodic high-low current etching with interval currents, achieving PSi PhCs with bandgaps precisely positioned at 532, 638, and 785 nm and reflectivity exceeding 80%. By adjusting interval current duration, pore size array was freely tuned to form 3D high-reflectivity microcavities with negligible optical loss. Based on this, strongly reductive Si-H bonds generated by etching enabled in situ growth of gold nanoparticles (Au NPs) in the microcavities, yielding Au NPs-X/PSi PhC chips (X = 532, 638, 785 nm) with high-density SERS hotspots while preserving optical modulation. When the SERS laser matched the PhC bandgap, synergistic photonic-plasmonic coupling enhanced the SERS intensity by 4-5 orders of magnitude over conventional Au NPs/Si chips. Finally, leveraging the chip's zero-background advantage, the Au NPs-785/PSi PhC chip matched with a 785 nm portable Raman spectrometer achieved highly sensitive analysis of single-stranded DNA (ss-DNA). This study proposes a feasible method for precise PSi PhC design and microcavity regulation, verifying its potential in biological detection.