Reflection-Enhanced Raman Identification of Single Bacterial Cells Patterned Using Capillary Assembly

Raman spectroscopy is an enticing tool for the rapid identification of pathogenic bacteria and has the potential to meet the demand for early diagnosis and timely treatment of patients. However, it remains a challenge to devise a reliable Raman detection platform to obtain reproducible signals from single bacterial cells. Herein, we utilize a reflective Ag/SiO₂ film that enhances the intrinsically weak Raman signals by re-excitation of the bacteria and reflection of downward-scattered photons, with maximum Raman intensities recorded by exciting the central edge of each single cell. The reflection-based configuration is simple, and its reliability as a sensing platform is validated by deep learning analysis. Importantly, given the positional dependence of the laser light on the Raman intensity, we employ capillarity-assisted particle assembly (CAPA) to selectively position single bacterial cells into a reflective topographical template to align the most Raman active region of the cell per the trap site geometry. Moreover, CAPA is utilized to directly isolate single cells from a suspension of artificial urine, eradicating any additional steps previously required to separate bacteria from biological samples. The proposed system has positive implications for future clinical settings that require simple, accurate, and reproducible detection of bacteria at the single-cell level.