A Versatile Photoinduced Electron Transfer-Based Upconversion Fluorescent Biosensing Platform for the Detection of Disease Biomarkers and Nerve Agent

Upconversion nanoparticles (UCNPs) have emerged to be a new family of fluorescent probes for bioanalytical applications. In a typical design, the UCNPs act as the energy donors in a fluorescence resonance energy transfer (FRET) system, in which the target molecules mediate the energy transfer from the UCNPs to the acceptors, and their quantity information is consequently converted into the on-off upconverting signals for readout. However, each UCNP contains thousands of emitting center ions and most of them are beyond the FRET critical distance, which hinders the fluorescence energy transfer efficiency, resulting in a low signal-to-background ratio (SBR). Herein, a new design is presented in which the energy of UCNPs is transferred to the o-quinones on their surface via the photoinduced electron transfer (PET) mechanism. In this system, the quenching efficiency of UCNPs' fluorescence can be up to 94.73%, providing a high SBR. The performance of the PET-based design is systematically testified, and the high-sensitivity detection of disease biomarkers (tyrosinase and alkaline phosphatase) is demonstrated. Moreover, this UCNP-PET platform is also capable of sensing the simulant of nerve agent sarin. This work will pave new ways to the design of UCNP-based platforms toward bioanalytical applications.