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.