A comparative study by the enzyme-linked immunofiltration assay of solid phases used in the development of flow immunosensors.

The application of an inert membrane-based, enzyme-linked immunofiltration assay (ELIFA) to the characterization of immunosorbents suitable for flow immunosensor development is described. For direct assays, eight monoclonal antibodies (MAb) raised against the insecticide carbaryl were immobilized on three sorbents, namely, controlled pore glass (CPG), hydrazide derivatized agarose beads and a hydrophilic polymer with immobilized Protein A/G. The interaction between immobilized antibodies and antigen was directly detected using a carbaryl hapten conjugated to horseradish peroxidase. Immunosorbent characterization was based on both sensitivity and re-usability. Optimal immunosorbent regeneration was achieved using 0.1 M glycine/HCl, pH 2.0 as the desorbent solution. The best covalent immunosorbent was obtained by immobilizing LIB-CNA36 MAb on hydrazide derivatized agarose beads. The best immunosorbent obtained by reversible immobilization was LIB-CNH45 MAb on Protein A/G. Using this support the eventual irreversible denaturation of covalently immobilized MAbs was overcome. For indirect assays, N-hydroxisuccinimide derivatized agarose beads and glutaraldehyde-activated CPG were used as sorbents for hapten immobilization via the amino groups of a carrier protein. In this format, antigen-MAb interactions were detected using a peroxidase-conjugated rabbit anti-mouse immunoglobulin. The highest sensitivity was achieved by LIB-CNH45 MAb in combination with derivatized agarose beads. All these results demonstrated the suitability of ELIFA as a fast, precise and easy-to-use technique for immunosorbent selection.