Microfabricated electrophoresis chip for bioassay of renal markers

A novel capillary electrophoresis chip-based detection system for simultaneous measurements of the renal markers creatine, creatinine, p-aminohippuric acid, and uric acid is described. Fluid control is used for mixing the sample with the enzymes creatininase (CA), creatinase (CI), and sarcosine oxidase (SOx) and for separating the neutral hydrogen peroxide end product from the anionic p-aminohippuric and urate species. The 'total' (creatinine and creatine) signal was measured with the running buffer containing all three enzymes, while the creatine signal alone was recorded by mixing the sample with the CI-SOx solution. Creatinine concentrations are measured by comparing the response in the presence and absence of CA. The peroxide product and the oxidizable p-aminohippuric and uric acids are detected electrochemically at a downstream gold-coated thick-film amperometric detector. The four renal markers are readily measured within 5 min, while creatinine/creatine within less than 2 min. Factors influencing the performance, including the level of three enzymes, separation voltage, and detection potential, are optimized. Applicability to urine samples is demonstrated. Such a multianalyte microchip detection device would allow renal function testing to be performed more rapidly, easily, and economically in the point-of-care setting.