Stimulated Raman Excited Fluorescence Spectroscopy and Imaging.

Powerful optical tools have revolutionized science and technology. The prevalent fluorescence detection offers superb sensitivity down to single molecules but lacks sufficient chemical information(1-3). In contrast, Raman-based vibrational spectroscopy provides exquisite chemical specificity about molecular structure, dynamics and coupling, but is notoriously insensitive(3-5). Here we report a hybrid technique of Stimulated Raman Excited Fluorescence (SREF) that integrates superb detection sensitivity and fine chemical specificity. Through stimulated Raman pumping to an intermediate vibrational eigenstate followed by an upconversion to an electronic fluorescent state, SREF encodes vibrational resonance into the excitation spectrum of fluorescence emission. By harnessing narrow vibrational linewidth, we demonstrated multiplexed SREF imaging in cells, breaking the "color barrier" of fluorescence. By leveraging superb sensitivity of SREF, we achieved all-far-field single-molecule Raman spectroscopy and imaging without plasmonic enhancement, a long-sought-after goal in photonics. Thus, through merging Raman and fluorescence spectroscopy, SERF would be a valuable tool for chemistry and biology.