Fluorescence immunoassay based on carbon dots as labels for the detection of human immunoglobulin G

Abstract

A rapid, selective and environmentally friendly fluorescence immunoassay strategy based on carbon dots (CDs) is developed for the detection of human immunoglobulin G (IgG, antigen). Firstly, in this protocol, CDs with high quantum yield were synthesized by hydrothermal process using citric acid as a carbon source and then carboxylated by bath sonication with NaOH and ClCH₂COONa. Subsequently, carboxyl-functionalized CDs were conjugated with goat antihuman IgG (gIgG, antibody) using an EDC–NHS amidization method to obtain the CDs-labeled gIgG, and this obtained conjugate CDs–gIgG was then incubated with a limited amount of human IgG for immunoreaction between antigen and antibody. The immunocomplex formed on the surface of carboxylated CDs resulted in the increase of fluorescence intensity. Under the optimal conditions, a linear relationship between fluorescence change ratio (F − F₀)/F₀ and human IgG concentration in a range from 0.05 to 2.0 μg mL⁻¹ was obtained with a detection limit of 0.01 μg mL⁻¹. This method has been successfully applied to the determination of IgG in human serum, with recoveries in the range of 95.8–111.5%. The results indicate the great promise for CDs as labels in fluorescence immunoassays.