Abstract
DNA chips represent miniaturized analytical tools that allow the simultaneous detection of different targets for high throughput screening. Recently, the application of polymer gels to DNA chips have been attracted special interest from the point of view of their high immobilization capacity for DNA. The important requirements for the gels are: (a) high diffusivity of the target DNA through the gel in the hybridization reaction, which is usually carried out at relatively high temperature, and (b) high transparency of the gel to measure the fluorescence intensity of the hybridized target DNA labeled by the fluorescent materials. In this work, we proposed thermosensitive porous gels to satisfy such demands. Thermosensitive gels swell in water at low temperature, but shrink above the intrinsic temperature because of the transition to the hydrophobicity. N-isopropylacrylamide (NIPAM) gel is a representative thermosensitive gel, with a transition temperature of about 32°C. By copolymerizing NIPAM, the cross-linker and the capture DNA above the transition temperature, the porous gel could be obtained easily. The gel was opaque, and consisted of the microgel particles and pores, which were formed by the phase separation in the polymerization process. The capture DNA might be immobilized on the surface of the microgel particles, because the phase separation between the hydrophobic poly(NIPAM) and the hydrophilic DNA occurs in the polymerization process. Polymer molecules such as target DNA could diffuse easily through such a porous gel. Furthermore, the porous gel synthesized with the selected compositions of NIPAM and the cross-linker became semitransparent by cooling below the transition temperature without supplying water. Because the microgel particles in the gel absorb the water in the pores, and as a result, the gel becomes non-porous.
