Comparative Analysis of Photoluminescence and Upconversion Emission from Individual Carbon Nanotubes for Bioimaging Applications

Luminescent single-walled carbon nanotubes (SWCNTs) are unique nanoemitters that allow near-infrared single-molecule detection within biological tissues. Interestingly, the recent discovery of upconversion luminescence from (6,5) SWCNTs provides a novel opportunity for deep tissue single SWCNT detection. Yet, the optimal excitation strategy for video-rate imaging of individual SWCNTs within live tissues needs to be determined taking into account the constraints imposed by the biological matter. Here, we directly compare the luminescence efficiencies of single (6,5) SWCNTs excited by continuous-wave lasers at their second-order excitonic transition, at their K-momentum exciton–phonon sideband, or through upconversion. For these three excitations spanning visible to near-infrared wavelengths, the relevance of single SWCNT imaging is considered inside brain tissue. The effects of tissue scattering, absorption, autofluorescence, and temperature increase induced by excitation light are systematically examined.