Evanescent wave immunoprobe with high bivalent antibody activity

Abstract We have determined the kinetic response of an evanescent wave optical fibre immunosensor and its absolute sensitivity. Using both kinetic methods and optical determinations of bound antigen, we infer that there are 2·4 × 10 11 active antibodies per cm 2 probe area. We estimate that 75% of the active antibodies are in the bivalent form, with both binding site capable of binding antigen. Using the kinetic data and optical measurements of the number of antigens bound to the fibre, we estimate that the unstirred dead layer thickness next to the fibre surface in the stirred solution, across which the antigens must diffuse, is 55 μm. Approximately 10 9 FITC labelled antigens are necessary to achieve a threshold signal, defined as 1% of the signal obtained when the fibre is saturated with antigen.

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