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 approximately 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 micrograms/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 micrograms/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 approximately 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.