Quantum dots assisted in vivo two-photon microscopy with NIR-II emission

With the advantages of high resolution and deep penetration depth, two-photon excited NIR-II (900–1880 nm) fluorescence (2PF) microscopic bioimaging is promising. However, due to the lack of imaging systems and suitable probes, few such works, to our best knowledge, were demonstrated utilizing NIR-II excitation and NIR-II fluorescence simultaneously. Herein, we used aqueously dispersible PbS/CdS quantum dots with bright NIR-II fluorescence as the contrast agents. Under the excitation of a 1550 nm femtosecond (fs) laser, they emitted bright 2PF in the NIR-II region. Moreover, a 2PF lifetime imaging microscopic (2PFLIM) system was implemented, and in vivo 2PFLIM images of mouse brain blood vessels were obtained for the first time to our best knowledge. To improve imaging speed, an in vivo two-photon fluorescence microscopy (2PFM) system based on an InGaAs camera was implemented, and in vivo 2PFM images of QDs-stained mouse brain blood vessels were obtained.