We propose a method to attach probe DNAs with a homogeneous population for quantitative measurement of a minimum number of target DNA/RNA for the next generation of DNA chip. To control the homogeneous population of DNA probes, polymer films having neighboring reactive groups at the same distance, i.e., aromatic polyurea film formed with 3,5-diaminobenzonic acid (DBA) and methylenedi(p-phenylene) diisocyanate (MDI) and aliphatic polyurea film formed with DBA and hexamethylene diisocyanate (HDI), were polymerized directly on the surface of a chip substrate by vapor deposition polymerization. The spatial arrangement and homogeneity of the reactive groups on the surfaces of the substrates were examined by observing the immobilization of DNA fragments bound to 20-nm gold nano-particles on the polymer films. The results showed that physical adsorption of the DNA was effectively inhibited on the DBA/HDI film in contrast to the DBA/MDI film and the conventional aminosilane surface. Moreover, the distribution of the particles was homogeneous on the DBA/HDI film, unlike on the other surfaces. These results indicate that the aliphatic polyurea film could be used to control the selectivity and uniformity of reactive groups on the surface of substrates for more precise quantitative measurement of DNA chip technology.
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