Polymer-coated optical fibres for application in a direct evanescent wave immunoassay Original Research Article

Three different polymers were tested for application in a direct evanescent wave immunoassay. For this purpose, 50 mm of a 200 μm plastic clad silica fibre was stripped off the cladding and coated with either 7% (w/w) polystyrene (n = 1.59) in tetrahydrofuran (THF), 7% (w/w) carboxylated poly(vinyl chloride) (PVC-COOH) (n = 1.55) in THF or chloropropyl-modified sol–gel (n = 1.56). Human IgG was immobilised on the polymer-coated fibres. The binding of immobilised IgG to TRITC-labelled anti-IgG was measured, and was highest on the sol–gel coated fibres. However, 80% of the measured signal was due to non-specific adsorption. Non-specific binding was negligible on polystyrene, but increased with increasing antibody concentration on PVC-COOH (from 9% to 45% for 0.5–5 μg ml−1 TRITC-labelled anti-IgG). 8 M urea, 0.1 M glycine/HCl and 0.1 M triethylamine were used for regeneration of the antigen–antibody complex 4 M NaCl. The solutions of NaCl and urea did not affect the stability of the complex. The use of 0.1 M glycine/HCl, however, resulted in a 65% regeneration of the complex on PVC-COOH and in a 35% regeneration on polystyrene. Sol–gel coated fibres could not be reused, because the porous structure of the gel was destroyed due to intrapore condensation of the regeneration solutions. The results were correlated to the characteristics of the polymers.