Development of Surface Nanostructure Control Method of Biomaterials by Utilizing Organosilane Monolayrs

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Alkyltrichlorosilanes, [2- (perfluorooctyl) ethyl] trichlorosilane (FOETS) and their mixed monolayrs were polymerized on the water subphase and were covalently immobilized onto the silicon wafer surface. Atomic force microscopic (AFM) observation of the (n-octadecyltrichlorosilane (OTS) /FOETS) mixed monolayr revealed that the crystalline OTS formed circular domains of ca. 1-2 mum in diameter, which were surrounded by an amorphous FOETS matrix. Lateral force microscopic (LFM) and scanning viscoelastic microscopic (SVM) observations of the (OTS/FOETS) mixed monolayr could also distinguish the difference in the physical and mechanical properties between domain and matrix. The (alkylsilane/FOETS) mixed monolayrs with shorter alkyl chain such as n-dodecyltrichlorosilane (DDTS) did not show the phase-separated structure maybe due to the lack in crystallinity of DDTS component. AFM observation of the [crystalline fatty acid (non reactive) /FOETS (reactive)] mixed monolayr also revealed the phase-separated structure. The crystalline fatty acid domain in the mixed monolayr was extracted by solvent and then, the monolayr of FOETS with the holes of ca. 1-2 mum in diameter, that is, the (Si/FOETS) monolayr was finally obtained. The Si phase of (Si/FOETS) was backfilled with the another organosilane by chemisorption. Then, the [(3-mercaptopropyl) trimethoxysilane (MTS) /FOETS] mixed monolayr was newly obtained by the chemisorption of MTS.The adsorption of bovine serum albumin (BSA) onto mixed monolayrs was studied by exposure of the mixed monolayrs to a BSA solution. BSA was preferentially adsorbed onto the MTS part due to a specific reaction between disulfide bond (-S-S-) in BSA and SH groups in MTS.On the other hand, in the case of (OTS/FOETS) mixed monolayr, BSA adsorbed preferentially onto the FOETS matrix in order to minimized the interfacial free energy in the aqueous environment.