Study on homogeneous competitive immune reaction by fluorescence correlation spectroscopy: Using synthetic peptide as antigen

In this paper, fluorescence correlation spectroscopy (FCS) is used for investigation of homogeneous immune reaction using synthetic peptide as antigen. The binding process of CA125 peptide antigen and its antibody was systematically investigated. The dissociation constant and dissociation rate for antigen–antibody complex were determined, which were kdiss = 0.94 ± 0.05 nM and koff = 0.00215 ± 0.0001 s−1, respectively. Under optimal conditions, the detection limit of the competitive immunoassay was 4 × 10−10 M (S/N = 3). The good recoveries were obtained with human serum samples. Our preliminary results demonstrated that the homogeneous competitive immunoassay based on FCS is simple, rapid, sensitive and small sample and reagent requirement, and this method maybe possess great potential applications in clinical diagnosis, food and environmental analyses and biological and biomedical studies.