The Dye-Sensitized Strategy Enhances the Performance of Upconversion Nanoprobes by Improving the Quenching Efficiency.

Luminescence resonance energy transfer (LRET) serves as the fundamental principle for constructing probes based on lanthanide-doped upconversion nanoparticles (UCNPs). The signal contrast of a UCNP-based probe is determined by the LRET efficiency, which directly limits the maximum signal-to-background ratio (SBR) and the limit of detection (LOD). To enhance the SBR, we developed a dye-sensitized upconversion nanoparticle, denoted as UCNPs@IR780, in which the upconversion luminescence (UCL) is efficiently quenched by LRET acceptors. The dye-sensitized upconversion emission originates from the UCNPs but is enhanced through dye-sensitization by the organic dye IR780. In addition to quenching the luminescence of UCNPs, simultaneous quenching of IR780 further suppressed the UCL, thereby improving the SBR. We employed MnO2 nanosheets as LRET acceptors, achieving a quenching efficiency of up to 90.8% for UCNPs@IR780. Upon interaction with glutathione (GSH), a molecule involved in numerous physiological processes, the MnO2 nanosheets were degraded, leading to recovery of the UCL signal. The system achieves a maximum SBR of 9.3 and an LOD of 0.1 µM for GSH. The improved SBR and LOD demonstrate that the dye-sensitized strategy effectively overcomes the inherent SBR limitations of conventional UCNP-based probes, thereby broadening their applicability in biosensing applications.