Bt toxin is currently the most widely used commercial biopesticide, especially in organic farming. It is usually applied as a mixture of cells, spores, and parasporal crystals. However, crystal preparations are easily inactivated by sunlight and degraded by microorganisms. To improve performance, insecticide crystals protein genes have been incorporated into the genome of some commercial agricultural plants. Bt toxin is then released into soil through root exudates and the recycling of crop residues.

The objective of this study is to investigate the interaction between Cry1Aa (the protein produced in rice Bt-transformed plant) and two models of minerals, glass and mica. Fluorescently labeled Bt solutions are flowing (laminar regime) between two flat walls of those materials. By normal scanning confocal fluorescence (S. Balme et al. J. Membr. Sci. 284 (2006) 198-204) between the two faces, it is possible to extract the instantaneous concentration profile in solution as well as the signal originating from the walls. We will present the first results showing the dependence of Bt adsorption on pH and ionic strength.