High detection sensitivity and fine chemical selectivity are of pivotal importance for microscopy. While fluorescence microscopy offers superb sensitivity, it is limited by its relatively poor selectivity. We recently reported electronic pre-resonance stimulated Raman scattering (SRS) microscopy by combining the superb sensitivity of electronic spectroscopy and chemical specificity of vibrational spectroscopy. In contrast, all the previous SRS microscopy is operated in the “non-resonance” region, in which the energy of the pump laser (ωpump) is well-below that of molecular absorption energy (ω0).
We identified an electronic pre-resonance SRS (epr-SRS) regime which represents an exquisite balance between signal enhancement and background suppression. In epr-SRS excitation, the energy of the pump laser (ωpump) is chosen to be close to but slightly lower than that of molecular absorption energy (ω0). The resulting epr-SRS microscopy has demonstrated detection sensitivity down to nano-molar concentration (about 1000 times higher than previous nonresonant SRS) with retained narrowband vibrational contrast for imaging and essentially no electronic background and little photo-bleaching.
L. Wei, Z. Chen, L. Shi, R. Long, A. V. Anzalone, L. Zhang, F. Hu, R. Yuste, V. W. Cornish and W. Min. “Super-multiplex vibrational imaging”, Nature, 544, 465 (2017).
