Natural and polyanionic heparin polysaccharide functionalized upconversion nanoparticles for highly sensitive and selective ratiometric detection of pesticide.

Pesticide contamination is a global concern, threatening human health and food safety. Herein, we developed heparin (HEP) functionalized upconversion nanoparticles (UCNPs)-based ratiometric nanosensor for the sensitive detection of 2,6-dichloro-4-nitroaniline (DCN) pesticide via inner filter effect. The strategy for HEP functionalization of UCNPs is based on adjusting the surface potentials of UCNPs with polyanionic HEP through the electrostatic interaction. UCNPs (NaYbF:Gd/Y/Tm@NaYbF@NaYF) was designed with core-shell-shell structure and extra sensitizer layer for efficient and strong upconversion luminescence (UCL) in the range of UV to NIR. After incorporation of DCN, the upconverted UV emission of UCNPs-HEP ratiometric nanosensor was considerably quenched with the NIR UCL at 800 nm remaining unchanged as internal standard. The UCNPs-HEP ratiometric nanosensor can achieve outstandingly selective and sensitive detection of DCN at the wide linear range of 5-300 μM with a detection limit of 0.41 μM. The remarkable applicability of the UCNPs-HEP ratiometric nanosensor was verified in apple, cucumber and grapes samples. The developed UCNPs-HEP ratiometric nanosensor with excellent biocompatibility and water dispersion capability, is promising for convenient, selective and sensitive sensing of DCN towards food and aqueous samples.