Recent advances in design of lanthanide-containing NIR-II luminescent nanoprobes

Luminescent biosensing in the second near-infrared window (NIR-II, 1000-1700 nm) region, which has weak tissue scattering and low autofluorescence, draws extensive attention owing to its deep tissue penetration, good spatial resolution and high signal-to-background ratio. As a new generation of NIR-II probes, lanthanide (Ln³⁺)-containing nanoprobes exhibit several superior properties. With the rapid development of Ln³⁺-containing NIR-II nanoprobes, many significant advances have been accomplished in their optical properties tuning and surface functional modification for further bioapplications. Rather than being exhaustive, this review aims to survey the recent advances in the design strategies of inorganic Ln³⁺-containing NIR-II luminescent nanoprobes by highlighting their optical performance optimization and surface modification approaches. Moreover, challenges and opportunities for this kind of novel NIR-II nanoprobes are envisioned.