Combinational Use of Antibody Affinities in an Immunoassay for Extension of Dynamic Range and Detection of Multiple Analytes

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Abstract
Here, we describe the coordinated use of two antibodies with different affinities in a single immunoassay to extend the dynamic range and to enable detection of multiple analytes. The combination of dual antibodies was permitted with a flow-based assay at the antibody concentration below the dissociation constant, enabling affinity to govern the antibody−antigen binding. Both high and low affinity antibodies to estriol were used in combination to extend the range. The binding of each antibody was mutually independent and individually occurred over concentration ranges of 10 pM−1 nM and 100 pM−1 μM. The wide dynamic range of 10 pM−1 μM was thus achieved as summation of the proportional signals to the total binding. When a combination of antibodies toward different antigens was used, it effectively detected multiple analytes within a mixture. In simultaneous analysis of a mixture of estradiol and estriol, the total signal was the sum of the binding signals from anti-estradiol and anti-estriol antibodies. In a further refinement, the individual antibodies were flowed through the flow cell sequentially, allowing the quantification of each binding signal within the combination. With this sequential format, measurement of the individual hormones in the range of 1.6 pM−1 nM was shown. Furthermore, the same flow format was successfully applied to assay estriol and estradiol hormones in mixtures of six related compounds.