Nonfluorescent\nNear-Infrared Surface-Enhanced Resonance\nRaman Nanoprobes with Ultrahigh Brightness and Synergistic Photothermal\nEffect

Near-infrared\n(NIR) surface-enhanced resonance Raman (SERRS) nanoprobes\nhave found wide applications in biomedicine; however, almost all of\nthese nanoprobes are fluorescent because the resonant Raman dyes used\ncannot be fully quenched onto the underlying plasmonic nanoparticles.\nTherefore, suppressing the fluorescence backgrounds in resonant Raman\nspectroscopy imaging is extremely important. In this work, we use\na black hole quencher, IQ1, as a Raman dye to develop absolutely nonfluorescent\nNIR resonant SERRS NPs. Ultrafast spectroscopy clarifies that the\nnonfluorescent mechanism of the dyes is attributed to the ultrafast\ninternal conversion at the subpicosecond scale, which quenches the\nfluorescence of excited states. The resultant nanoprobes exhibit zero\nfluorescent background, femtomolar-level sensitivity (100 fM) as well\nas superb photostability (τ = 10006 s) without fluorescence\nphotobleaching, outperforming that of fluorescent counterparts. More\nimportantly, the SERRS NPs show a synergistic photothermal effect\noriginating from the dye molecule-plasmon interactions, achieving\na high photothermal conversion efficiency of 64.94%. Featuring these\nexcellent properties, these SERRS NPs allow for longitudinally photostable\ncellular imaging and enhanced photothermal elimination of cancer cells.\nTo the best of our knowledge, this is the first example of absolutely\nnonfluorescent NIR SERRS NPs, opening up promising applications for\nimproved phototheranostics.