Hollow Au nanoparticles for single-molecule Raman spectroscopy via a synergistic electromagnetic and chemical enhancement strategy

Raman spectroscopy has demonstrated significant potential in molecular detection, analysis, and identification, particularly when it adopts single-molecule surface-enhanced Raman scattering (SM-SERS) substrates. A recent SM-SERS scheme incorporates two-fold Raman enhancement mechanisms: the electromagnetic enhancement enabled by a plasmonic nanogap hotspot formed from gold sphere nanoparticles sitting on a gold mirror and the chemical enhancement enabled by a two-dimensional material, WS₂, inserted into the nanogap. In this work we integrate multiple advanced concepts and techniques to achieve remarkable performance improvements of SM-SERS. We have used hollow gold nanoparticles to form plasmonic nanogaps, which better match the wavelength of near-infrared pump lasers, thus maximizing the electromagnetic field enhancement within the nanogap and creating a more effective hotspot. Notably, our strategy has achieved universal, robust, fast, and uniform SM-SERS detection of three dye molecules (Rhodamine B, Rhodamine 6G and Crystal Violet) with a detection limit of 10 mol L^-1. This innovative approach opens up new possibilities for bringing state-of-the-art optical imaging, monitoring, and spectroscopy technologies into the single-molecule science arena for disclosing more unknown physical, chemical, and biological properties and principles.