Control of Biological Surface States on Chlorine-Doped Amorphous Silica Particles and Their Effective Absorptive Ability for Antibody Protein.

Amorphous silica particles (ASPs) have low biotoxicity and are used in foodstuffs; however, the adsorption states of proteins on their surfaces have not yet been clarified. If the adsorption states can be clarified and controlled, then a wide range of biological and medical applications can be expected. The conventional amorphous silica particles have the problem of protein adsorption due to the strong interaction with their dense silanol groups and denaturation. In this study, the surfaces of amorphous silica particles with a lower silanol group density were modified with a small amount of chlorine during the synthesis process to form a specific surface layer by adsorbing water molecules and ions in the biological fluid, thereby controlling the protein adsorption state. Specifically, the hydration state on the surface of the amorphous silica particles containing trace amounts of chlorine was evaluated, and the surface layer (especially the hydration state) for the adsorption of antibody proteins while maintaining their steric structures was evaluated and discussed. The results showed that the inclusion of trace amounts of chlorine increased the silanol groups and Si-Cl bonds in the topmost surface layer of the particles, thereby inducing the adsorption of ions and water molecules in the biological fluid. Then, it was found that a novel surface layer was formed by the effective adsorption of Na and phosphate ions, which would change the proportion of the components in the hydration layer. In particular, the proportion of the free water component increased by 21% with the doping of chlorine. Antibody proteins were effectively adsorbed on the particles doped with trace amounts of chlorine, and their steric adsorption states were evaluated. It was found that the proteins were clearly adsorbed and maintained the steric state of their secondary structure. In the immunoreactivity tests using streptavidin and biotin, biotin bound to the chlorine-doped particles showed efficient reactivity. In conclusion, this study is the first to discover the surface layer of the amorphous silica particles to maintain the steric structures of adsorbed proteins, which is expected to be used as a carrier particle for antibody test kits and immunochromatography.

Mechanochemical Solid-State Immobilization of Photofunctional Dyes on Amorphous Silica Particles and Investigation of Their Interactive Mechanisms.

Amorphous silica particles (ASPs) have been reported to exhibit bioactive properties and are becoming the focus of attention as bioceramics. However, their interactions with proteins in living organisms remain to be understood and need to be investigated in order to achieve wider applications. Our research group found that chlorine (Cl)-containing ASPs are useful for protein immobilization. Photofunctional dyes (fluorescein (FS-), methylene blue (MB+)) that have the carboxy and amino groups as the main functional groups were immobilized on the Cl-containing ASPs via the mechanochemical method as the model molecule and their spectral properties were used to investigate and discuss the organic/inorganic interfacial bonding states. In FS-, the oxygen atoms of the carboxy groups in the molecule were immobilized by the hydrogen bonds with the silanol groups on the ASPs surfaces, indicating that there is an optimum Cl content for the immobilization as the monomer state. In the case of MB+, as the Cl concentration in the ASPs increases, the immobilization via the electrostatic interactions between the Cl in the ASPs and the terminal dimethylamino group, and the hydrogen bonding between the N atoms of the MB+ hetero ring and the particle silanol group were enhanced. These results mainly suggest that the protein adsorption system occurs through the hydrogen bonding between the carboxy groups of the protein and the silanol groups on the particles and via electrostatic interactions between the amino groups of the protein and the dissociated silanol groups and the contained Cl at the particles. Thus, the spectral characterization using dyes as probes is expected to predict the protein interactions with the amorphous silica particles.