NIR-II emitting quantum dots for multiplex in vivo imaging and light-sheet imaging

Abstract

Quantum dots (QDs) emitting at the second near-infrared region (NIR-II; wavelength = 1000–1700 nm) offer unique opportunities as a deep tissue penetrating probe. NIR-II light provides enhanced spatial resolution (~10 μm) through deep tissue due to suppressed photon scattering and near-zero autofluorescence. It affords facile and multiplexed modalities, and QDs can have bright and wavelength-tunable photoluminescence at NIR-II. PbS/CdS (Core/Shell) QDs were sophisticatedly prepared to have sufficient brightness and narrow fluorescence bandwidth to allow multiplexing at NIR-II. A polymer encapsulation technique provided the QDs with long-term fluorescence stability over a week in biological media and offered simple bioconjugations. As a proof-of-concept experiment, two NIR-II QD probes were prepared as two-color multiplexed imaging probes, and a home-built NIR-II imaging setup provided multiplexed and nearly real-time longitudinal whole-body level in vivo imaging. Mixture solution of the two NIR-II QDs was intravenously injected to a tumor-xenografted mouse model and the NIR-II signals from the two channels were longitudinally observed, which empowered simultaneous and direct comparison of the tumor targeting ability for QDs with targeting moiety over the unconjugated control QDs. In addition, three-dimensional images were obtained and analyzed by home-built NIR-II light-sheet imaging setup.