An Upconversion nanoprobe based on basic fuchsin functionalized Upconversion nanoparticles for detecting nitrite

Nitrite (NO₂^-) is a common pollutant in environmental and food matrices, and excessive intake poses a significant risk to human health. Therefore, the development of highly sensitive and selective detection methods is of great importance. Herein, we report a novel upconversion nanoprobe (UCNPs) for the determination of NO₂^- in acidic media based on the inner filter effect (IFE). In this system, citrate-modified upconversion nanoparticles (Cit-UCNPs) serve as the energy donor, while basic fuchsin (BF) functions as the energy acceptor. Under acidic conditions, NO₂^- is converted to nitrosyl cations (NO⁺), which can specifically attack the electron-rich secondary amine groups of BF. This structural modification effectively interrupts the IFE process between BF and Cit-UCNPs, thereby restoring the upconversion luminescence of the nanoparticles. Under optimized conditions, the developed probe exhibits a sensitive response to NO₂^- with a detection limit as low as 1.03 μM (S/N = 3), and demonstrates excellent anti-interference performance. This work not only provides a new strategy for the rapid and sensitive detection of NO₂^-, but also offers valuable insights for the design of IFE-based upconversion luminescence probes.