Fluorescein isothiocyanate linked immunoabsorbent assay based on surface-enhanced resonance Raman scattering.

By using fluorescein isothiocyanate (FITC) as a Raman probe, we have developed a simple and sensitive method for an immunoassay based on surface-enhanced resonance Raman scattering (SERRS). For the first time, a SERRS-based immunoassay on the bottom of a microtiter plate is reported. We have applied the main pretreatment method of enzyme-linked immunoabsorbent assay (ELISA) to the present study. In this method, SERRS spectra of FITC are measured after several continuous steps of antigen coating, blocking, antibody adding, and colloidal silver staining. Human immunoglobulin G (IgG) and FITC-antihuman IgG are used for the immunoreaction. The proposed method has several advantages for immunoassay. First, we can determine the concentration of antigens via the intensity of a SERRS signal of FITC molecules that are attached to antibodies without an enzyme reaction, and thus the process is simple and reagent saving. Second, one can obtain SERRS spectra of FITC directly from silver aggregates on the bottom of a microtiter plate without displacement. Third, by using SERRS of FITC, the present method is sensitive enough to detect antigens at the concentration of 0.2 ng/mL, which is comparable to ELISA. Results are presented to demonstrate that the proposed SERRS-based immunoassay may have great potential as a high-sensitivity and high-throughout immunoassay.