Fig. 1

Characterization and optical properties of NIR-IIb emitting RNase A@PbS/ZnS QDs. A Schematic design of RNase A@PbS/ZnS QDs. B Fluorescence emission spectrum of RNase A@PbS/ZnS QDs. C High-resolution TEM image and HAADF-STEM images of as-prepared RNase A@PbS/ZnS QDs. The energy-dispersive X-ray spectroscopy elemental maps showed the distribution of Pb (blue), Zn (yellow), and S (red). Scale bar: 5 nm. D Photostability of RNase A@PbS/ZnS QDs under continuous 808-nm laser exposure for 2 h. E The long-time stability of RNase A@PbS/ZnS QDs stored at room temperature (20–25 °C) over the course of 4 weeks. F Fluorescence images of capillary tubes filled with PbS QDs or RNase A@PbS/ZnS QDs immersed at varied depths in 1% Intralipid (LP, long-pass). These results confirmed the excellent fluorescence properties and stability of RNase A@PbS/ZnS QDs, which suggested the superior fluorescence imaging potential in the NIR-IIb region