Micro analysis system for pH and protease activities with an integrated sample injection mechanism.

A micro analysis system for the electrochemical determination of the activity of protease along with pH sensing was fabricated aiming for its use in telemetric micro analysis systems targeting the testing of the stomach and intestines. The system consisted of a pH-sensing site and two protease assay sites formed in polydimethylsiloxane (PDMS) micro flow channels. To introduce sample solutions, valves were formed with gold electrodes in the inlets, which functioned on the basis of electrowetting. An external sample solution could be introduced into the sensing sites by switching on the valves at appropriate times. In the pH-sensing site, a pH-indicator electrode changed its electrode potential immediately after a sample solution reached an internal liquid-junction reference electrode. The slope of the calibration plot was -74.5 mVpH(-1). Bovine serum albumin (BSA) was used as the substrate for the enzyme and was spotted on the wall of the flow channel that faced the pH-indicator electrode of the protease assay sites. The release of protons accompanying the hydrolysis of BSA by the enzyme was detected using the pH-indicator electrode. When trypsin was contained in the sample solution as a test enzyme, a distinct decrease in pH, which was dependent on the trypsin activity, was observed, indicating that enzymatic hydrolysis was proceeding. The initial rate of potential change varied in proportion to the activity in a range between 1.0 and 51.7 Uml(-1). The integration of the microfluidic and sensing functions provides significant advantages for the use of this system as an isolated telemetric micro system that might operate with small batteries.