Microchip-Based Capillary Electrophoresis for Immunoassays:  Analysis of Monoclonal Antibodies and Theophylline

A microchip capillary electrophoresis device has been used to separate the reaction products of homogeneous, immunological reactions within 40 s. Determination of monoclonal mouse IgG in mouse ascites fluid, via a direct assay, and the drug theophylline in serum samples, via a competitive assay, was demonstrated on-chip. The mouse anti-bovine serum albumin IgG assay gave a linear calibration curve up to at least 135 μg/mL, with ±3% precision. The theophylline assay gave a threshold for detection of 1.25 ng/mL in diluted serum. A calibration curve of signal vs undiluted log[theophylline] is linear from 2.5 to 40 μg/mL, which includes the therapeutically useful range. Theophylline recoveries in spiked samples were 100%, within an experimental error of ±5%. A buffer system consisting of 0.05 M tricine adjusted to pH 8.0, 0.01% (w/v) Tween 20, and 40 mM NaCl was used. This buffer allowed for adequate separation (40 000 plates for theophylline; 1000 plates for theophylline−antibody complex and for human IgG) and gave reproducibility of migration times of 1−1.5% over 4-day periods, indicating minimal problems from adsorption in the uncoated chips.