Poor maximal adsorption of antigen on bare silica against sustained maximal adsorption onto cationized silica. 18 kDa-hsp adsorption onto SiO2/DODAB particles (A-B) or bare SiO2 particles (C-D) in 5 mM Tris.HCl, pH 7.4. Interaction between particles and protein took place for 1 h at 25°C. Final silica and DODAB concentrations are 0.1 mg/ml and 0.05 mM, respectively. 18 kDa-hsp M. leprae adsorption was expressed either as adsorbed 18 kDa-hsp M. leprae concentration in mg/ml (A and C) or as number of 18 kDa-hsp M. leprae molecules adsorbed per m2 silica (B and D).