Fluorescence lifetime imaging microscopy with subdiffraction-limited resolution

In this study, we demonstrate subdiffraction-limited fluorescence lifetime imaging microscopy (FLIM) by engineering the point spread function (PSF) with stimulated emission depletion (STED). The enhanced spatial resolution allows the number of fluorophores in the PSF to reduce in turn the associated heterogeneity in lifetime analysis. Moreover, time gating can be performed using time-correlated single photon counting (TCSPC) to carefully select detected fluorescence photons so as to optimize the spatial resolution and the signal-to-noise ratio in STED imaging. This flexibility also supports the removal of the unintended effects of lifetime reduction that is caused by STED pulses.