Characterization of fluorescence lifetime of organic fluorophores for molecular imaging in the shortwave infrared window

Abstract

Significance: Fluorescence lifetime imaging in the shortwave infrared (SWIR) is expected to enable high-resolution multiplexed molecular imaging in highly scattering tissue.Aim: To characterize the brightness and fluorescence lifetime of commercially available organic SWIR fluorophores and benchmark them against the tail emission of conventional NIR-excited probes.Approach: Characterization was performed through our established time-domain mesoscopic fluorescence molecular tomography system integrated around a time-correlated single-photon counting-single-photon avalanche diode array. Brightness and fluorescence lifetime were measured for NIR and SWIR probes >1000 nm. Simultaneous probe imaging was then performed to assess their potential for multiplexed studies. Results:The NIR probes outperformed SWIR probes in brightness while the mean fluorescence lifetimes of the SWIR probes were extremely short. The phantom study demonstrated the feasibility of lifetime multiplexing in the SWIR window with both NIR and SWIR probes.Conclusions: Long-tail emission of NIR probes outperformed the SWIR probes in brightness >1000 nm. Fluorescence lifetime was readily detectable in the SWIR window, where the SWIR probes showed shorter lifetimes compared to the NIR probes. We demonstrate the feasibility of lifetime multiplexing in the SWIR window, which paves the way for in vivo multiplexed studies of intact tissues at improved resolution.