Silica particles coated with zwitterionic polymer brush: Formation of colloidal crystals and anti-biofouling properties in aqueous medium

Silica particles (SiP) were modified with 2-bromoisobutyryl group-carrying silane coupling reagent, and a polymer brush of carboxymethylbetaine, poly[1-carboxy-N,N-dimethyl-N-(2'-methacryloyloxyethyl)methanaminium inner salt] (PolyCMB), was introduced onto surface of the particles using surface-initiated atom transfer radical polymerization (ATRP). After purification by simple ultrafiltration, the layer of the PolyCMB brush-carrying silica particle (SiP-PolyCMB) in aqueous medium showed a clear iridescence at the bottom of a quartz cell upon a slow sedimentation, indicating the formation of colloidal crystals due to both electrostatic and steric repulsion between the particles. The peak of the reflection spectra gradually shifted to a smaller wavelength region due to the formation of more densely packed ordered structure of the SiP-PolyCMB. Moreover, SiP-PolyCMBs dispersed in water showed neither salt- nor freeze-thaw cycle-induced coagulation, and were resistant against the non-specific adsorption of proteins such as bovine serum albumin and egg white lysozyme, which is in contrast with the noticeable adsorption of the proteins to the bare silica particles. (C) 2010 Elsevier B.V. All rights reserved.