CHARACTERIZATION OF BIOMEMBRANES BY SPECTRAL ELLIPSOMETRY, SURFACE-PLASMON RESONANCE AND INTERFEROMETRY WITH REGARD TO BIOSENSOR APPLICATION

Phospholipid bilayers with transport proteins and antigen/antibody int erfaces are considered to be suitable biosensor systems. The quality o f such membranes or interfaces depends on the properties of the layers . Optical methods have proved to be an appropriate tool for characteri zing those layers in situ and in a non-destructive manner. Two systems with potential for biosensor applications are characterized by some o f these methods: phospholipid bilayer membranes spread from vesicle so lution and protein-antigens both adsorbed on planar solid support. The results of spectral ellipsometry, surface plasmon resonance (SPR) and spectral interferometry are compared with respect to quality of chara cterization, expenditure of sample preparation and measurement, and ti me resolution. The phospholipid membranes adsorbed show a relatively l ow refractive index and a relatively high thickness. Bruggeman effecti ve medium approximation is used to calculate the effective layer thick ness. This result is compared to SPR measurements. A correlation betwe en thickness and vesicle concentration may be detected. Further, the t est protocol of an immunoassay is examined by spectral interferometry and SPR. Thicknesses determined are compared to results obtained by ap plying spectral ellipsometry. The data measured by ellipsometry are in agreement with the molecular dimensions of the immunoglobulins. Diffe rences between details can be explained by physical considerations.