Microfluidic device for high-sensitivity coulometric detection of proteins

The sensitivity of a coulometric sensing device was enhanced by combining it with metallization and used for the detection of proteins. Alpha-1-fetoprotein (AFP) was used as a model analyte. Microfabricated flow channels were used to process solutions. Hydrogen peroxide produced by the enzymatic reaction of glucose oxidase (GOD) bound to protein-antibody complexes was oxidized on a platinum electrode. Silver was deposited simultaneously on a platinum electrode in a different flow channel, connected to the first via a liquid junction. The amount of deposited silver was measured by coulometry. The sensitivity and detection limit were improved by increasing the incubation time of the enzymatic reaction. After incubation for 120 min a detection limit of 0.4 ng/mL (3σ) was achieved. The sensing device may be suitable for use as a diagnostic instrument for on-site testing.