A ratiometric upconversion nanosensor for visualized point-of-care assay of organophosphonate nerve agent

A novel nanosensor based on upconversion nanoparticles, NaYF 4 : Yb, Tm@NaYF 4 , covalently conjugated with fluorogen Rhodol (Rhodol-UCNPs) for the sensitive and point-of-care detection of organophosphonate nerve agent mimic DCP has been fabricated. This nanosensor exhibited upconversion luminescence turn-on and ratiometric detection ability of DCP with satisfactory response speed (within 40   s) and a detection limit of 0.21   μM. Under a 980   nm laser excitation, the blue emission of UCNPs was quenched due to the luminescence resonance energy transfer (LRET) between Rhodol and Tm 3+ doped UCNPs, while the presence of DCP led to the suspension of LRET, as a result, significant fluorescence recovery of UCNPs could be observed. Furthermore, we have developed paper-based devices for the point-of-care detection of DCP with naked eyes, both the color change and the blue fluorescence recovery could inform us the presence of DCP. Such convenient detection strategies have the potential to provide us early warnings of the existence possibilities of any risks from OP nerve agents and thus ensure us of our public security.