Detection of choline and hydrogen peroxide in infant formula milk powder with near infrared upconverting luminescent nanoparticles

Choline is an essential nutrient for the growth and development of the baby, and therefore it is often added to infant formula. In this paper, a novel sensor for choline determination in infant formula is developed based on upconverting nanoparticles (UCNPs) with near infrared luminescence. UCNPs-based detection can avoid the interference of background fluorescence from complex samples, and thus provide high selectivity and sensitivity. It was observed that in the presence of Fe3+, polyacrylic acid coated UCNPs were quenched to 3% of its original intensity. The degree of quenching was among the best for UCNPs. Hydrogen peroxide could oxidize Fe2+ to Fe3+, which caused quenching of the upconversion luminescence. A new H2O2 detection method was thus established. In addition, choline could be hydrolyzed to betaine by choline oxidase, and at the same time produced H2O2, which also caused luminescence quenching through Fe2+ oxidation. Therefore, selective choline sensing was achieved.