Lanthanide-based upconversion nanoparticles (UCNPs) offer excellent photostability and large anti-Stokes shifts but are often limited by poor environmental responsiveness, hindering sensing applications. To address this challenge, we developed an energy-relay strategy by integrating near-infrared (NIR) dyes with Er3+/Tm3+ doped UCNPs. Under 980 nm excitation, Yb3+ transfers energy to Tm3+ and Er3+, excited Tm3+ ions then pass their energy to NIR dyes such as Cy7.5, which subsequently relay it back to Yb3+ ions, enabling a second Yb3+-to-Er3+ energy transfer. This cascade process amplifies Er3+ emission while quenching Tm3 + emission. In Cy7.5-modified Er3+/Tm3+ doped UCNPs (NaYbF4:Er@NaYbF4@NaYbF4:Tm@NaYbF4@NaLuF4), the energy-relay effect enhances the Er3+/Tm3+ ratiometric signal by two orders of magnitude. The process is highly dependent on the dopant architecture, as swapping Er3+ and Tm3+ positions disrupts the relay. The generality of this strategy is supported by similar energy-relay observed with Cy7 and IR806. Despite the incorporation of dyes, our energy-relay design retains the excellent photostability characteristic of lanthanide upconversion while introducing environmental responsiveness. As a proof of concept, the energy-relay nanoprobe demonstrated high sensitivity in both thermal and chemical sensing. Our findings establish energy-relay engineering as a versatile design principle for designing stable, efficient, and responsive upconversion nanoprobe platforms.
Li et al. (Wed,) studied this question.