SiO2 thin-films were prepared by thermal oxidation method. It showed uniform color based on the thin-film interference of visible light. Then we made biotin antenna on the top of SiO2 thin-film. Biotin is one of the vitamins and it has high association constant with protein avidin. After immersed the substrate into avidin solution, certain color changes based on the self-assembling of avidin on its surface were observed. By the immersing these substrates into mono-dispersed polystyrene particle solution, a polystyrene particle layer was formed onto avidin SAMs and it brought dynamic interference color change. As a result, this substrate could sense the avidin molecules over 1.0×10-8M of its concentration by naked eyes.
Interference color is well known as one of the systems to display various colors. By using this system, we tried to develop novel method for the brief estimation of molecular sorption and diffusion in polymer thin-film. We prepared polymer thin-film (polystyrene and polyvinyl alcohol) on the silicon substrate by spin-coat method and dipping method. Reflected visible light at air/polymer and polymer/silicon are interfered each other, and prepared thin-film showed various colors depending on its thickness and refractive index. By the sorption of various small molecules, polymer thin-films swelled and its interference color changed drastically. Degrees of changes in thickness and refractive index of polymer thin-film are able to be estimated by the degree of interference color changes and Bragg's law and Snell's law. An almost linear relation between thickness changes in polymer thin-film and solubility parameter was observed by the reflective VIS spectrum measurements of prepared polymer thin-films under various solvent vapors. By this simple method, molecular sorption and diffusion behavior in polymer thin-film could be visualized. This system will give anew brief method for the estimation of polymer -penetrant affinity.
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