Characterization of digoxigenin-labeled B-phycoerythrin by capillary electrophoresis with laser-induced fluorescence. Application to homogeneous digoxin immunoassay

A laser-induced fluorescence (LIF) immunoassay technique based on capillary electrophoretic (CE) separation is demonstrated. The analysis of digoxin in serum at clinically useful concentration levels of 10(-9) to 10(-10) M is achieved using this technique. The chemistry presented here using digoxigenin-labeled B-phycoerythrin was selected as a convenient model for the exploration of CE-LIF-based immunoassays. The LIF system described here exhibits detection limits in the low 10(-11) M range for several common fluorophores. The data presented in this report are one of the first examples of nanomolar quantitative analysis in a human serum matrix by CE.