Dye-sensitized cascaded energy transfer for amplified 1525 nm luminescence in highly doped lanthanide nanoparticles

Lanthanide-based probes for second near-infrared (NIR-II) luminescence imaging enable deep-tissue penetration with minimal autofluorescence. However, their broader application is hindered by intrinsic limitations such as low brightness and weak absorption. To address these, we developed a dye-sensitized construct, NaErF 4 @NaYF 4 :50%Yb@ICG. This design harnesses population dynamics in heavily doped Er 3+ systems through a cascaded energy transfer process enabled by dual 808 nm excitation of both indocyanine green (ICG) and the Er 3+ -rich core—specifically, it harvests energy destined for nonradiative decay by inserting a Yb 3+ -mediated relay (ICG → Yb 3+ → Er 3+ ) into the original ICG → Er 3+ pathway. This approach yields 1965-fold and 11-fold enhancements in 1525 nm downshifting emission compared to the corresponding core and counterpart, respectively. The resulting nanoprobe enables high-resolution NIR-IIb vascular imaging with a signal-to-background ratio of 3.09. These mechanistic insights and design principles inform the design of efficient NIR-II nanoprobes, demonstrating substantial potential for advancing vascular biology.