Surface modification for realizing implantable biosensors

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It is important for implantable immune-sensors by using ion-sensitive field-effect transistor(ISFET)to immobilize antibody-protein with high density and high activity. In this research, we use plasmapolymerized membrane for the career of inunobilized antibody. We use Hexamethyldisiloxane(HMDS), which is excellent in adhesion to silicon substrate, for the materials of organic membrane, and fabricate the membrane by plasma-polymerized method. We introduce SH-groups on the surface of organic membrane as functional group to inunobilize antibody by applying glow-discharge treatment to ethanedithiol having SH-groups. We confirm that hydrohibic surface becomes hydrophobic by this surface modification. The contact angle of the surface tension, which was 125ﾟ with water, turns 52ﾟ after modification. The fact that XPS signals of sulfur is observed only in the modificated membrane, is the evidence that SH-groups are introduced. Cysteine is covalently immobilized by SS-bond on the surface. The an … More tibody(anti-Human Serum Albrffin IgG)is covalently immobilized with crosslinking NH_2-groups of cysteine and SH-groups of antibody F_<ab>' hinge together with bifunctional reagent. The activity immobilized activated antibody density is of the order of 10^<11>[cm^<-2>](the closest density is 2X10^<12>)by enzymeimmunoassey(EIA), which shows high density immobilization. To investigate quantity of non-specific adsorption, organic membrane having no immobilized antibody is similarly measured by EIA. As a result, the membrane introduced SH-groups and Cysteine has less non-specific adsorption than that of NH_2-groups. We measure the changing of surface potential of this immobilized antibody caused by antigen-antibody binding. A surface potential change of the order of 0.1 mV is observed at the antigen concentration of 0.01 - 1 mg/ml. We attain the same result in the case that the antigen coexists with other substances(Bovine Serum). This result suggests the possibility of realizing immune-sensors. Less