Fiber-Optic Immunosensors Based on Continuous Reagent Delivery

Immunoassay technology has advanced tremendously during the past 30 years and has provided indispensable tools for clinical and environmental analysis. The immunoassays in use are highly sensitive, with some achieving femto- and attomolar detection limits. These assays possess a variety of drawbacks due mainly to the demand for trained technical personnel and intensive sample manipulations. The introduction of fiber optics offers the potential for miniaturization and simplification. Some examples of fiber-optic immunosensors have been described in the literature. Most of these face the usual immunosensor limitation of single-use detection; hence, they are not appropriate for continuous use. The main limitation of all immunosensors lies in the strong antibody-antigen binding, which requires either extensive washing for long periods of time or use of chaotropic reagents for dissociation. Several examples of regenerable fiber-optic sensors are based on displacement of a labeled by an unlabeled antigen or by an antibody developed especially to possess decreased binding affinity. In our laboratory, research is concentrated on developing a continuous fiber-optic sensor based on prolonged delivery of reagents from slow-release polymers. In this paper we review the achievements in the area of continuous sensing with fiber-optic immunosensors, describe the use of slow-release polymers to deliver reagents necessary for the immunoassay, and comment on the advantages and the limitations of the technique.