The determination of thickness and surface mass density of mesothick immunoprecipitate layers by null ellipsometry and protein 125iodine labeling |
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Authors: | Benesch Johan Askendal Agneta Tengvall Pentti |
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Institution: | Applied Physics, IFM, Link?pings Universitet, Link?ping SE-581 83, Sweden. |
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Abstract: | The aim of the present study was to ellipsometrically determine the thickness and surface mass density in air for up to 110-nm-thick organic layers made of alternatingly deposited layers of HSA and polyclonal anti-HSA on hydrophobic silicon. The ellipsometrically determined thickness was compared to that obtained by AFM and the deposited surface mass density calibrated with (125)I-labeled proteins. The results indicate a good agreement in protein layer thickness between AFM and ellipsometry when the protein film refractive index N(film)=1.5-0i, although then the calculated surface mass density from the ellipsometry data became grossly overestimated by the Cuypers one-component formula. A good agreement in the surface mass density was obtained when the M/A ratio in this formula was lowered from 4.14 to 2.35. This approach indicates a convenient means of determining the refractive indices and surface mass densities of mesothick organic layers proteins on solid supports. |
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