Partial plasma polymerization for coexistence of hydrophobic/hydrophilic area in several ten micrometer size is the typical technique for protein patterning. A hydrophobic hexamethyldisiloxane plasma-polymerized film (HMDS PPF) was deposited on a glass substrate and this surface was partially modified by subsequent nitrogen plasma treatment (hydrophilic surface, HMDS-N PPF) with a patterned shadow mask. An antibody protein (F(ab')2 fragment of anti-human immunoglobulin G) was selectively adsorbed onto the HMDS-N area and was not adsorbed onto the HMDS area. Distinct 8080 µm2 square spots surrounded by a non-protein adsorbed 80 µm-wide grid were observed. Then, when the protein modified by fullerene was used, the reversible patterning was obtained. This indicated that the modification by fullerene changed the hydrophilic nature of F(ab')2 protein to hydrophobic one, as a result, the modified protein was selectively adsorbed onto hydrophobic area.

Endothelial cell adhesion and growth were investigated on three types of surfaces with a plasma-polymerized coating (PPC): (1) the pristine surface of a hexamethyldisiloxane (HMDS) PPC (hydrophobic, electrically neutral surface); (2) an HMDS PPC surface with nitrogen-containing plasma treatment (hydrophilic, positively charged surface); and (3) an HMDS PPC surface treated with oxygen plasma (hydrophilic, negatively charged surface). Endothelial cells grew on surface (2) but not on surfaces (1) or (3). Next, endothelial cell adhesion and growth was investigated on a surface on which 80-µm squares were micro-patterned at 160-µm intervals in a mosaic composed of two different (cell-adhesive and non-cell-adhesive) regions. Cell growth on the patterned surfaces was different from that on non-patterned surfaces. PPC was shown to be a simple process for modulating cell adhesion to surfaces.

Techniques for patterned modification of substrate surfaces are important for forming microarrays on protein chips. A hexamethyldisiloxane plasma-polymerized film (HMDS PPF) was deposited on a glass substrate and the resulting surface was partially modified by subsequent nitrogen plasma treatment with a patterned shadow mask. When surface adsorption of an antibody protein (F(ab')2 fragment of anti-human immunoglobulin G) was visualized by fluorescence microscopy, distinct 8080 µm2 square spots were observed, surrounded by a non-fluorescent 80 µm-wide grid. This pattern could be attributed to proteins selectively adsorbed onto the nitrogen plasma-treated regions but not onto the surface of pristine HMDS PPF. This provided a simple fabrication method of protein patterning.

Adsorption of antibody protein (anti-human IgG) onto plasma-polymerized thin films (PPF) with nanoscale thickness was characterized by atomic force microscopy (AFM) and quartz crystal microbalance (QCM). The PPF surface is very flat (less than 1 nm roughness) and its properties (charge and wettability) can be easily changed while retaining the backbone structure. We focus on two types of surfaces: one is the pristine surface of hexamethyldisiloxane (HMDS) PPF (hydrophobic) and the other is an HMDS PPF surface with nitrogen-plasma treatment (hydrophilic and positive-charged surface). The AFM image showed that the antibody molecules were densely adsorbed onto both surfaces and individual antibody molecules could be observed. The QCM profiles show a corresponding tendency with the AFM images. These results indicate that the plasma polymerized film can be the suitable biointerface for the application of biosensor and bioassay.