Highly sensitive multiplex-detection of surface-enhanced Raman scattering via self-assembly arrays of porous AuAg nanoparticles with built-in nanogaps

Designing and fabricating highly dense porous nanoparticles (p-NPs) arrays with nanogaps are crucial for ultra-sensitive surface-enhanced Raman scattering (SERS) detection as they can provide both abundant built-in and inter nanogap-induced hotspots. Here, we demonstrate highly sensitive multiplex-detection of organic dyes using SERS substrates with the self-assembly arrays of porous AuAg alloy (p-AuAg) NPs. The p-AuAg NPs were fabricated by a thermal dewetting method of very thin Au/Ag bilayers and a subsequent dealloying approach, which result in multiple built-in and inter nanogaps between the nano-granules with a porous structure and the adjacent NPs as well as excellent porosity and a high surface-to-volume ratio. The SERS substrates with p-AuAg NPs for the detection of Rhodamine 6 G (R6G) molecules exhibited an excellent enhancement factor of approximately 7.8 × 10⁶, good reproducibility with relative standard deviation<6.5%, and limit of detection of dye molecules down to 2.37 × 10⁻⁹ M concentration in comparison with the AuAg alloy NPs. This is attributed to the generation of significant enhancement of electromagnetic field at the highly-dense built-in and inter nanogap in the self-assembly arrays of p-AuAg NPs, which is supported by the finite-difference time-domain (FDTD) simulation results. In addition to the detection of R6G molecules, the multiplex detection capability of R6G and crystal violet (CV) molecules at low concentrations for the p-AuAg NPs-based SERS substrates was also demonstrated. These findings present a potential pathway towards the development of an excellent SERS platform for practical applications such as bioscience, food, and environmental safety.