Quantification of thyroxine by the selective photoluminescence quenching of l-cysteine-ZnS quantum dots in aqueous solution containing hexadecyltrimethylammonium bromide

The determination of l-thyroxine is proposed based on the photoluminescence quenching effect caused on the l-cysteine modified ZnS quantum dots (l-cysteine ZnS QDs) aqueous dispersion. Under optimum conditions, the analytical response followed a Stern-Volmer model and the experimental conditions were adjusted to enable a robust and reproducible photoluminescence signal. The linear response observed in the quantum dots aqueous dispersion covered the l-thyroxine concentration from the LOQ (2.0×10−8 mol L−1) to 4.0×10−6 mol L−1. The approach was tested in the determination of l-thyroxine in pharmaceutical formulations used to treat patients with thyroid gland disorder. The percent recoveries in controlled samples were between 93.3 and 103%. Analyte fortified saliva was also evaluated as a possible sample for l-thyroxine monitoring of a patient under treatment. It was identified a static type of photoluminescence quenching caused by l-thyroxine.