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 similar to 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 mu g/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 mu g/mL, which includes the therapeutically useful range. Theophylline recoveries in spiked samples were 100%, within an experimental error of +/-5%. A buffet system consisting of 0.05 M tricine adjusted to pH 8.0, 0.01% (w/v) Tween 20, and similar to 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.