Deep-red polymer dots with bright two-photon fluorescence and high biocompatibility for in vivo mouse brain imaging

Bright deep-red emissive P dots were synthesized and their two-photon fluorescence (2PF) properties were systematically studied under 720-960 nm fs laser excitations. They were found to have large two-photon absorption (2PA) cross-sections and good biocompatibility. They were then utilized for in vivo 2PF imaging of brain blood vessels of mice under a commercial two-photon scanning microscope, and a large penetration depth of 720 µm with high contrast was obtained.298