Near-infrared-II Ag-based quantum dots for fluorescence imaging

Compared with traditional near-infrared-I (NIR-I, 700–900 nm) fluorescence imaging, near-infrared-II (NIR-II, 1000–1700 nm) fluorescence imaging has unique advantages such as lower background fluorescence, higher sensitivity, and the ability to achieve higher tissue penetration depth and spatial resolution in vivo imaging. Therefore, NIR-II fluorescence imaging technology has great development potential in many applications such as surgical navigation, highly sensitive tumor detection, biosensing, and immunoassay. Among numerous NIR-II fluorescent nanomaterials, Ag-based (Ag2X; X = S, Se, Te) quantum dots (QDs) have attracted great research interest due to their advantages such as adjustable size, tunable wavelength range, high stability, and low toxicity. In recent years, scientists have made many efforts in the controllable synthesis, bandgap modulation, and fluorescence enhancement of Ag-based QDs, making them widely used in biomedical research. Based on this, this review introduces the optical characteristics, synthesis methods, and fluorescence optimization strategies of Ag-based QDs, systematically summarizes the latest research progress of these nanomaterials in NIR-II fluorescence imaging, and looks forward to the problems that need to be solved and the future development trends.