Raman identification of single nucleotides flowing through permeable plasmonic films.

Surface-Enhanced Raman Scattering has been studied for decades as a recognition technique due to its high sensitivity and discriminative power, particularly in biological applications. Inspired by nanopore sequencing technology, we developed a plasmonic device capable of operating in a flow-through configuration to detect individual molecules passing through plasmonic hotspots. This device is a permeable plasmonic film, through which single molecules are sequentially delivered via electrophoresis, while Raman spectra are recorded in real-time. A very effective light-matter coupling, combined with the ultrasmall size of plasmonic spots, enabled access to angstrom spatial and microsecond temporal scales compatible with polymer sequencing. We successfully slowed the translocation process and captured Raman spectra of the four nucleotides at a time resolution down to 20 μs under our experimental conditions. We achieved a discrimination accuracy of 89% at the single-molecule level. Also, we demonstrated a spatial resolution on the order of a few nucleotides, suggesting the potential for sequencing applications.