A new reagentless immunosensor for measuring IgG concentration in human plasma based on fluorescence-enhancement immunoassay

Based on the enhancement of fluorescein isothiocyanate (FITC) fluorescence caused by binding to proteins, we developed a reagentless immunosensor to directly determine immunoglobulin G (IgG) in human plasma. The fluorescence-enhancement immunoassay (FEI) is used in only limited conditions in spite of its simplicity, because the homogeneous reagent cannot be reused. In the present study, a new FEI was evaluated with an immobilized reagent. FITC was used to label protein A, which has specific reactivity with IgG. The FITC-labeled protein A was immobilized on nylon membrane and placed in a fluorometer cell. It produced fluorescence enhancement corresponding to IgG concentration in phosphate-buffered saline (PBS) and bovine serum solution, and it responded to IgG also in human plasma. Thus the IgG concentration can be determined directly using the reagentless immunosensor based on FEI.