Ultrastable and Biocompatible NIR-II Quantum Dots for Functional Bioimaging

Fluorescence bioimaging in the second near-infrared spectral region (NIR-II, 1000-1700 nm) can provide advantages of high spatial resolution and large penetration depth, due to low light scattering. However, NIR-II fluorophores simultaneously possessing high brightness, good stability, and biocompatibility are very rare. Hydrophobic NIR-II emissive PbS@CdS quantum dots (QDs) are surface-functionalized, via a silica and amphiphilic polymer (Pluronic F-127) dual-layer coating method. The as-synthesized PbS@CdS@SiO2@F-127 nanoparticles (NPs) are aqueously dispersible and possess a quantum yield of approximate to 5.79%, which is much larger than those of most existing NIR-II fluorophores. Thanks to the dual-layer protection, PbS@CdS@SiO2@F-127 NPs show excellent chemical stability in a wide range of pH values. The biocompatibility of PbS@CdS@SiO2@F-127 NPs is studied, and the results show that the toxicity of the NPs in vivo could be minimal. PbS@CdS@SiO2@F-127 NPs are then utilized for in vivo and real-time NIR-II fluorescence microscopic imaging of mouse brain. The architecture of blood vessels is visualized and the imaging depth reaches 950 mu m. Furthermore, in vivo NIR-II fluorescence imaging of gastrointestinal tract is achieved, by perfusing PbS@CdS@SiO2@F-127 NPs into mice at a rather low dosage. This work illustrates the potential of ultrastable, biocompatible, and bright NIR-II QDs in biomedical and clinical applications, which require deep tissue imaging.