Surface lanthanide activator doping for constructing highly efficient energy transfer-based nanoprobes for the on-site monitoring of atmospheric sulfur dioxide.

The sensitive and on-site detection of sulfur dioxide (SO2) is in great demand in the fields of food safety and environmental protection. Here, we developed a novel upconversion nanoprobe based on the luminescence energy transfer mechanism for monitoring the atmospheric SO2 concentrations. The lanthanide emitters, Tm3+ ions, were optimized to be doped on the surface layer of the upconversion nanoparticles to improve their energy transfer efficiency by minimizing the distance between the emitters and the surface quencher, a cyanine dye. As a proof-of-concept, the optimal nanoprobe was utilized to detect SO2 water derivatives, bisulfite ions, exhibiting a linear luminescence increase in the range of 1 nM to 10 nM. Furthermore, we assembled the cyanine-modified upconversion nanoparticles onto a test paper, and used a smartphone-based detection platform to achieve portable and visual detection of SO2. The test paper showed a strong luminescence stability, homogeneity and good anti-interference. The limit of detection for SO2 gas was found to be 1 ng L-1. This novel upconversion test paper was also demonstrated to directly monitor the concentration of SO2 gas in atmosphere.