Determination of Hydrocortisone in Cosmetics by CdSe/CdS Quantum Dots‐Based Fluoroimmunoassay Using Magnetic Fe3O4/Au Nanoparticles as Solid Carriers

Abstract

AbstractThis work demonstrated the feasibility of detecting hydrocortisone in cosmetics using a novel CdSe/CdS quantum dots‐based competitive fluoroimmunoassay with magnetic core/shell Fe3O4/Au nanoparticles (MCFN) as solid carriers. Hydrocortisone antigen was labeled with the synthesized core/shell CdSe/CdS quantum dots (QDs) to form the antigen‐QDs conjugate. Meanwhile, hydrocortisone antibody was incubated with MCFN and the immobilized antibody was obtained. The immobilized antibody was then mixed sequentially with hydrocortisone and a slightly excess amount of the QDs‐labeled hydrocortisone antigen, allowing their competition for binding with the antibody immobilized on MCFN. The bound hydrocortisone and the antigen‐QDs conjugates on MCFN were removed subsequently after the mixture was applied to a magnetic force. The analyte concentration was obtained by measuring the fluorescence intensity of the unbound hydrocortisone antigen‐QDs conjugates. The proposed method was characterized by simplicity, rapidity, and high sensitivity with a wide linear working range of 0.5 to 15000 pg·mL−1 and a low detection limit of 0.5 pg·mL−1. The proposed method was successfully applied to the determination of hydrocortisone in cosmetics with satisfactory results.