Bright quantum dots emitting at ∼1,600 nm in the NIR-IIb window for deep tissue fluorescence imaging

Significance In vivo fluorescence imaging in near IR-IIb window (1,500–1,700 nm) can provide high spatial and temporal resolution and deep tissue penetration for fundamental research and potential translations. Herein, a bright fluorescent probe emitting at ∼1,600 nm based on lead sulfide (PbS)/CdS quantum dots was developed. The CdS shell helped to chemically passivate and retain the high fluorescence of the PbS core after phase transfer to aqueous solutions for biocompatibility. The 1,600-nm emitting probe allowed noninvasive, millimeter-deep fluorescence imaging at high speeds up to 60 frames per second with micrometer-scale spatial resolution in 2D wide-field and 3D confocal modes. The probes were nontoxic and largely excreted over 1 month, providing a tool for in vivo research of preclinical animal models.