The Method of Total Internal Reflection Ellipsometry in Biosesing:
A. Nabok, A. Tsargorodskaya, N.F. Starodub and A. Holloway
Sheffield Hallam University, UK
spectroscopic ellipsometry, SPR, total internal reflection, immune assay, nonylphenol, QCM, AFM
The method of Total Internal Reflection Ellipsometry (TIRE), which was recently proposed as a combination of spectroscopic ellipsometry and SPR light coupling configuration, was exploited in this work for detection of nonylphenol, an oestrogen-mimicking compound, in water. The method of TIRE showed great potential for bio-sensing as a very sensitive optical analytical technique. The combination of TIRE with direct immune assay approach, i.e. specific binding of nonylphenol molecules to immobilised antibodies, allowed the registration of the above toxin in low concentrations down to 1 ng/ml. The TIRE study of kinetics of binding reaction revealed its high specificity with typical association constants in the range of 10^6 (l /mol). The detailed study of the mechanism of nonylphenol binding, using complementary experimental methods of QCM Impedance and AFM, allowed us to suggest a novel mechanism of binding of large aggregates (micelles) of amphiphilic molecules of nonylphenol to respective antibodies. This leads to a substantial increase in the thickness of adsorbed layers in TIRE experiments, and in the anomalously large added mass and film softening in QCM impedance study. The existence of large aggregates on the surface was confirmed directly with AFM.
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Nanotech 2006 Conference Program Abstract