Microfluidic device for freshness or ageing determination of food materials

A plug-based electrochemical microdevice was fabricated for on-site determination of freshness or ageing of foods. As indicators to represent the state, the K-value or the concentration of inosine monophosphate (IMP) was used. Two sets of thin-film three-electrode systems were located in a flow channel. Mechanisms to form liquid plugs, to merge the plugs, and to place the plug on the electrode area were integrated. To obtain the K-value, total concentrations of ATP-related compounds that appear in the numerator and denominator of the equation were measured using the electrodes in the upper and lower streams, respectively. For the determination of IMP, inosine and hypoxanthine in a sample solution were removed enzymatically, and hydrogen peroxide produced in enzymatic reactions including that of alkaline phosphatase was detected. Characterization using standard solutions revealed that the values agreed well with those calculated from the known concentrations.