(523d) Fractal Analysis of Binding and Dissociation Kinetics of Cancer Markers on Biosensor Surfaces

A fractal analysis is presented for the binding and the dissociation of different cancer markers on biosensor surfaces. The data analyzed include putrescine in solution to PDDA/APTES/MWCNT/PuO-modified GCE (glassy carbon electrode (Rochette et al., 2005), and vascular endothelial growth factor (VEGF) in solution to the soluble form of the VEGF receptor (sFlt-1 or VEGF-1) immobilized on a sensor chip surface (Barleon et al., 1996). Single- and dual-fractal models were used to fit the data. Values of the binding and the dissociation rate coefficient(s), affinity values, and the fractal dimensions were obtained from the regression analysis provided by Corel Quattro Pro 8.0. The binding rate coefficient and the affinity values are sensitive to the degree of heterogeneity present on the sensor chip surface. Predictive equations are developed for the binding rate coefficient as a function of the heterogeneity present on the biosensor chip surface. For example, the binding kinetics of different concentrations of putrescine (25-100 micromolar) in solution to a PDDA poly(diallyldimethylammonium) chloride/APTES (3-aminopropyltrietoxy-silane)/MWCNT (multi-walled carbon nanotube/PuO (putrescine oxidase)-modified GCE (glassy carbon electrode) in 0.05 M phosphate buffer were analyzed. The binding rate coefficient, k of putrescine in solution to plasma from a tumor-disposed mouse or a healthy mouse exhibits an order of dependence between second and two and one-half order on the fractal dimension, Df or the degree of heterogeneity that exists on the biosensor surface. Similarly, for the binding of VEGF in the 5-2250 ng/mL concentration range in solution to its receptor (sFlt-1) immobilized on a biosensor chip surface the binding rate coefficient, k exhibits an order of dependence between one and one-half and second on the VEGF concentration in solution. The analysis presented provides physical insights into these cancer-biomarker-receptor reactions occurring on the different biosensor surfaces.