Analysis of protein adsorption characteristics to nano-pore silica particles by using confocal laser scanning microscopy

The effect of average pore size of nano-pore silica particles on protein adsorption characteristics was determined experimentally by the dissociation constant and the adsorption capacity determined from the Langmuir equation. As the average pore size was increased from 2.2 to 45 nm, the BSA adsorption capacity increased from 16.8 to 84.3 mg/g-silica so as the equilibrium constant (from 2.6 to 9.4 mg/ml). Using confocal microscopy with fluorescence labeling, we could visualize the protein adsorption in situ and determine the minimum pore size required for efficient intraparticle adsorption. The confocal microscopy analysis revealed that BSA was adsorbed mainly on the surface of the particles with a smaller pore size, but diffused further into the interstitial surface when it was sufficiently large. It was concluded that for BSA whose Stoke's diameter is ca. 3.55 nm the minimum pore size of about 45 nm or larger was required for a sufficient adsorption capacity.