Controlled surface adsorption of fd filamentous phage by tuning of the pH and the functionalization of the surface

Abstract

The surface adsorption of fd filamentous phage (fd phage) dispersed in different solution pHs was investigated with functionalized SiO2/Si substrates. The fd phages at high pH (similar to 9.0) were well-adsorbed on the SiO2/Si surface that was functionalized by 3-aminopropyltriethoxysilane, whereas those at low pH (similar to 3.0) were well-adsorbed on the cleaned SiO2/Si surface. The high affinity of the carboxylic acid groups (COO-) at high pH (similar to 9.0) was attributed to the fact that they give a higher adsorption to the positively charged amine groups (NH3+) on the surface of the substrate, similar to the effect of H3O+ at low pH (similar to 3.0) in a solution on the surface of the hydroxyl groups on the substrate (OH-). Interestingly, the aligned structures of the fd phage at intermediate pH (similar to 7.0), caused by the locally positively charged coat protein of the fd phage and the shear forces along the washing and blowing direction, were identified. The effective spring constant of the fd phage bundles was estimated to be 0.672 N/m using a force-distance curve. Our results offer prerequisite information for the bottom-up assembly in SiO2/Si substrates using the fd phage in bionanoelectronics. (C) 2011 American Institute of Physics. [doi:10.1063/1.3549113]