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Fractal Binding and Dissociation Kinetics of Heart-Related Compounds on Biosensor Surfaces

Ajit Sadana and Atul M. Doke. Chemical Engineering, University of Mississippi, Anderson Drive, Oxford, MS 38677-1848

A fractal analysis is presented for the binding and dissociation of different heart-related compounds in solution to receptors immobilized on biosensor surfaces. The data analyzed include LCAT (lecithin cholesterol acyl transferase) concentrations in solution to egg-white apoA-I rHDL (high density lipoprotein) immobilized on a biosensor chip surface (Jin et al., 1999), native, mildly-oxidized, and strongly-oxidized LDL (low density lipoprotein) in solution to a heparin modified Au-surface of a surface plasmon resonance (SPR) biosensor (Gaus and Hall, 1999), and TRITC-labeled HDL in solution to a bare optical fiber surface (Singh and Poirier, 1993). Single- and dual-fractal models were employed to fit the data. Values of the binding and dissociation rate coefficient(s), affinity values, and the fractal dimensions were obtained from the regression analysis provided by Corel Quattro Pro 8.0 (Corel Corporation Limited, 1997). The binding rate coefficients are sensitive to the degree of heterogeneity on the sensor chip surface. Predictive equations are developed for the binding rate coefficient as a function of the degree of heterogeneity present on the sensor chip surface and on the LCAT concentration in solution, and for the affinity as a function of the ratio of fractal dimensions present in the binding and in the dissociation phases. The analysis presented provides physical insights into these analyte-receptor reactions occurring on different biosensor surfaces. Generally, it is seen that an increase in the fractal dimension of the surface or the degree of heterogeneity leads to an increase in the binding rate coefficient. One possible explanation of the observed increase could be due to the fact that the fractal surface (roughness) leads to turbulence, which enhances mixing, decreases diffusional limitations, and leads to an increase in the binding rate coefficient (Martin et al., 1991).