Microfabricated electrophoresis chips for simultaneous bioassays of glucose, uric acid, ascorbic acid, and acetaminophen

A micromachined capillary electrophoresis chip is described for simultaneou s measurements of glucose, ascorbic acid, acetaminophen, and uric acid. Flu id control is used to mix the sample and enzyme glucose oxidase (GOx). The enzymatic reaction, a catalyzed aerobic oxidation of glucose to gluconic ac id and hydrogen peroxide, occurs along the separation channel. The enzymati cally liberated neutral peroxide species is separated electrophoretically f rom the anionic uric and ascorbic acids in the separation/reaction channel. The three oxidizable species are detected at the downstream gold-coated th ick-film amperometric detector at different migration times. Glucose can be detected within less than 100 s, and detection of all electroactive consti tuents is carried out within 4 min. Measurements of glucose in the presence of acetaminophen, a neutral compound, are accomplished by comparing the re sponses in the presence and absence of GOx in the running buffer. The repro ducibility of the on-chip glucose measurements is improved greatly by using uric acid as an internal standard. Factors influencing the performance, in cluding the GOx concentration, held strength, and detection potential, are optimized. Such coupling of enzymatic assays with electrophoretic separatio ns on a microchip platform holds great promise for rapid testing of metabol ites (such as glucose or lactate), as well as for the introduction of high- speed clinical microanalyzers based on multichannel chips.