Resonant Strategy in Designing NIR-II SERS Nanotags: A Quantitative Study

Surface-enhanced Raman scattering (SERS) nanotags have garnered much attention for in vivo and intraoperative imaging due to their high sensitivity and intrinsic fingerprint spectrum. Recently, in vivo bioimaging at the second biological near-infrared (NIR-II) window has demonstrated significant advances with better spatial resolution and deeper tissue penetration. The development of SERS nanotags at the NIR-II window are therefore highly desired. The resonant strategy, i.e., the use of resonant substrates and resonant molecules, can be helpful in fabricating bright SERS nanotags at the NIR-II window; however, this strategy has not been demonstrated with the lack of quantitative assessments. Here we report a quantitative study on the Raman enhancements of the resonant strategy in preparing NIR-II SERS nanotags. By comparing the resonant and nonresonant plasmonic nanorod substrates, the resonant substrates have been shown to provide an enhancement factor of up to 4 orders of magnitude. When using the resonant Raman reporter molecules, SERS intensities can be further increased by 25-546 times. This work demonstrates the potential of the resonant strategy in fabricating ultrasensitive NIR-II SERS nanotags and provides insights into the design of related plasmonic devices.