Nonfluorescent Near-Infrared Surface-Enhanced Resonance Raman Nanoprobes with Ultrahigh Brightness and Synergistic Photothermal Effect.

Near-infrared (NIR) surface-enhanced resonance Raman (SERRS) nanoprobes have found wide applications in biomedicine; however, almost all of these nanoprobes are fluorescent because the resonant Raman dyes used cannot be fully quenched onto the underlying plasmonic nanoparticles. Therefore, suppressing the fluorescence backgrounds in resonant Raman spectroscopy imaging is extremely important. In this work, we use a black hole quencher, IQ1, as a Raman dye to develop absolutely nonfluorescent NIR resonant SERRS NPs. Ultrafast spectroscopy clarifies that the nonfluorescent mechanism of the dyes is attributed to the ultrafast internal conversion at the subpicosecond scale, which quenches the fluorescence of excited states. The resultant nanoprobes exhibit zero fluorescent background, femtomolar-level sensitivity (100 fM) as well as superb photostability (τ = 10006 s) without fluorescence photobleaching, outperforming that of fluorescent counterparts. More importantly, the SERRS NPs show a synergistic photothermal effect originating from the dye molecule-plasmon interactions, achieving a high photothermal conversion efficiency of 64.94%. Featuring these excellent properties, these SERRS NPs allow for longitudinally photostable cellular imaging and enhanced photothermal elimination of cancer cells. To the best of our knowledge, this is the first example of absolutely nonfluorescent NIR SERRS NPs, opening up promising applications for improved phototheranostics.