Antigen-antibody diffusion-limited binding kinetics of biosensors: a fractal analysis

A fractal analysis is made of antigen-antibody binding kinetics in various biosensor applications reported in the literature. Both sensor configurations are considered, wherein (a) the antigen is in solution and the antibody is immobilized on the fibre-optic surface, and (b) the antibody is in solution and the antigen is immobilized on the fibre-optic surface. For example, when the antigen is immobilized, an increase in the antibody concentration (anti-Ars) in solution leads to (a) an increase in the fractal dimension value and hence the state of disorder or roughness, and (b) a higher rate coefficient for binding on the fibre-optic surface. An analysis of the influence of different parameters on the fractal dimension values for a particular effect, such as a comparison of fresh and regenerated immunosensors, helps to clarify the conformational states and reactions occurring on the fibre-optic surface. Examination of the different cases presented together provides novel physical insights into the state of disorder or roughness on the surface. This research should contribute towards techniques for manipulating the reactions occurring on fibre-optic surfaces in desired directions.