An immunoassay performed using a microchip electrophoretic system is d
escribed, Separation and quantitation of free and bound labeled antige
n in a competitive assay are carried out in channels micromachined int
o fused silica substrates. Such microchips are attractive because of t
heir small size, ruggedness, and amenability to automated handling. Th
e assay achieves the determination of cortisol in blood serum over the
range of clinical interest (1-60 mu g/dL) without the need for extrac
tion or other sample preparation steps. The separation is performed in
less than 30 s. Very high throughput is possible by operating the ass
ay in multiple channels in parallel, These characteristics make microc
hip electrophoretic systems a promising technology for the rapid analy
sis of clinical samples.