We are developing biosensors with specific surface structures that are highly sensitive to virus or marker molecules. We need to suppress unwanted adsorption and detect target materials selectively. As shown in Fig. 1, controlled adsorption, target-antibody reaction, and signal amplification techniques are being investigated. When antibodies are immobilized on a substrate with inappropriate molecular orientations, their activity to capture the antigens will be lost. It is therefore necessary to know the density and orientation of the antibodies on the surface in order to characterize the performance of the sensing chip. Using atomic force microscopy (AFM), one of the nanotechnology characterization methods, the structure and density of small materials adsorbed on a flat substrate can be observed.

Figure 2 (a) shows an AFM image of the sensor surface, N-N'-carbonyldiimidazole (CDI) reacted with an aminosilane monolayer film on a silicon oxide layer formed on a glass substrate. Figure 2 (b) is an AFM image of a CDI surface to which are attached antibodies for the influenza virus. Under the conditions used for the process, spherical objects are observed with a density of 100-200 particles/µm². Judging from the distributed heights, we believe that the antibodies are adsorbed with various orientations.

Fabrication of micropatterned substrates to control cell adhesion and proliferation is a promising technique for cell-based technologies, including the screening of drug candidate libraries and fundamental investigations of cell-cell communication. Although several successful strategies for creating cellular micropatterns on substrates have been demonstrated, a complex multistep process and requirements for special and expensive equipment or materials limit their prevalence as a general experimental tool. To circumvent these problems, we are conducting research focused on serum albumin which is most abundant protein in blood.

We have established a novel simple fabrication method for a micropatterned surface for cell patterning using serum albumin. As shown in Fig. 3(a), we were able to prepare a water-insoluble, cross-linked albumin film possessing the properties of native albumin, such as resistance to cell adhesion and drug-binding ability^[1]. In addition, we found that the cell nonadhesive surface property could be easily changed to allow cell adhesion by exposing the cross-linked albumin film to UV light or cationic polymer solution^[2][3]. Cellular micropatterns were created on substrates and inside a microfluidic device by utilizing the convertible cell-adhesion property of the cross-linked albumin film (Fig. 3(b)) ^[4]. We will apply this method to other bio-related substances to control their behavior of adsorption to material surfaces.