NIR-II fluorescence in vivo confocal microscopy with aggregation-induced emission dots.

Significantly reduced tissue scattering of fluorescence signals in the second near-infrared (NIR-II, 1,000-1,700 nm) spectral region offers opportunities for large-depth in vivo bioimaging. Nowadays, most reported works concerning NIR-II fluorescence in vivo bioimaging are realized by wide-field illumination and 2D-arrayed detection (e.g., via InGaAs camera), which has high temporal resolution but limited spatial resolution due to out-of-focus signals. Combining NIR-II fluorescence imaging with confocal microscopy is a good approach to achieve high-spatial resolution visualization of biosamples even at deep tissues. In this presented work, a NIR-II fluorescence confocal microscopic system was setup. By using a kind of aggregation-induced emission (AIE) dots as NIR-II fluorescent probes, 800 μm-deep 3D in vivo cerebrovascular imaging of a mouse was obtained, and the spatial resolution at 700 μm depth could reach 8.78 μm. Moreover, the time-correlated single photon counting (TCSPC) technique and femtosecond laser excitation were introduced into NIR-II fluorescence confocal microscopy, and in vivo confocal NIR-II fluorescence lifetime microscopic imaging (FLIM) of mouse cerebral vasculature was successfully realized.