Quantitative interpretation of the optical textures of liquid crystals caused by specific binding of immunoglobulins to surface-bound antigens

We report a quantitative analysis of the change in optical appearance of a supported film of liquid crystal that is induced by specific binding of an immunoglobulin (IgG) to a surface-bound antigen. We interpret the optical a ppearance to indicate the amount of bound IgG and thus the concentration of IgG in solution. The procedure is a simple one to perform, requiring use o f a CCD camera and a polarized white light source. We use the average gray scale brightness of the optical appearance of the supported liquid crystal to construct an optical response curve as a function of the amount of anti- biotin IgG bound to surface-immobilized biotin. We interpret the optical re sponse curve using a model based on statistical binding of antibody to the surface and a cooperative response of the nematic liquid crystal to the bou nd antibody. Because the amount of bound antibody is largely controlled by mass transport of the antibody to the surface and thus the concentration of IgG in solution, the optical appearance of the liquid crystal can be corre lated to the concentration of IgG in solution. We measured changes in the g ray scale brightness of the liquid crystal over 2 orders of magnitude of co ncentration of IgG in solution (1-100 nM). Our results also suggest that co nvection and geometry can be used to increase the dynamic range and sensiti vity of the liquid crystal to the concentration of IgG in solution.