Seeing, Counting, Identifying, and Distinguishing Single Molecules from Their Mixtures via Raman Spectroscopy

Seeing, counting, identifying, and distinguishing molecules one by one in their mixture phases is recognized as a big challenge in molecular science. Here we employ this using a single-molecule surface-enhanced Raman spectroscopy (SM-SERS) strategy combining giant electromagnetic enhancement (EME) from plasmonic nanogaps and giant chemical enhancement (CME) from monolayer WS₂. For a dilute mixture of rhodamine B (RhB), rhodamine 6G (R6G), and crystal violet (CV) at concentrations of as low as 10^-16 M, this SM-SERS substrate enables the sighting, counting, identification, and distinction of individual molecules. High-credibility results are achieved rapidly (50 ms acquisition) using 785 nm near-infrared laser excitation to record and analyze distinct Raman spectra. This EME-CME synergy SM-SERS strategy offers a powerful capability of optically probing and monitoring the spatial-temporal evolution of the physical, chemical, and biological properties of molecules, which would open up a new frontier of molecular science.