DIRECT MONITORING OF ANTIGEN-ANTIBODY INTERACTIONS BY SPECTRAL INTERFEROMETRY

Spectral interferometry as a tool for on-line monitoring of immunoreactions is described. The setup consists of a light source, a thin transparent light interference layer as the sensing interface and a diode array spectrometer. Optical coupling is achieved by means of a bifurcated fiber optics. The basic principle is the measurement of the reflection spectra perpendicular to the sensing film. Incident light is partially reflected at the adjacent and remote surfaces of this film. The reflected partial beams show interference resulting in an interference spectrum. Deposition of a layer of protein at the interface during an immunoreaction changes the reflected spectrum. If the refractive indices of film and protein layer are matched, the change in the interference spectrum can be calculated as an increase in the thickness of the film. The reaction of rabbit-IgG with anti-rabbit-IgG on polystyrene shows high specificity. All steps of the test protocol can be clearly identified by changes in layer thickness. Quantitative evaluation of concentration dependency shows a linear correlation between antibody concentrations and initial rate of thickness increase. Investigated concentrations range from 0.5-25-mu-g/ml. Data can be calculated from a time interval of 100 s incubation time, indicating the capability of this rapid label-free system.