Detection of immunological reaction with the attenuated total reflection (ATR) technique

The sensitivity of the attenuated total reflection (ATR) technique to surface modifications allows the study of biological or medical phenomena where solutions segregate to form a layer on the walls of the sample holder. We present an immunoassay study of IgG antigen reacting with specific antibodies in saline solution on an aluminum thin-film attached to a prism, forming the bottom of the container where the reaction takes place. During the reaction a layer is adsorbed on the aluminum film showing a resonant absorption peak in the reflected signal that shifts towards larger angles of incidence at every step of the reaction. These shifts are related to the optical properties and the thickness of the adsorbed layers and may be quantified. This work presents the experimental setup and qualitative results of this reaction.