Microdevice for on-site fish freshness checking based on K-value measurement.

An electrochemical microfluidic device with two sensing sites in the upper and lower streams of a flow channel was fabricated to measure the K-value as a means of evaluating the freshness of fish. In this device, plugs of solutions were processed using mechanisms to place a plug at the sensing site and to merge and mix two plugs in a single flow channel. The sums of ATP-related compound concentrations used for the calculation of the K-value were measured at the first and second sensing sites. The ratio of the output currents agreed well with the K-value calculated from predetermined concentrations in standard solutions. The K-values of jack mackerel, yellow tail, and sea bream extracts were then obtained using the device and were found to agree well with those obtained by high-performance liquid chromatography (HPLC). In addition, the changes in the K-value with time were observed to depend strongly on the type of fish for these three fish extracts.

Electrochemical microdevice for on-site determination of rice freshness.

An electrochemical microdevice was fabricated for on-site rapid freshness determination of rice. The activity of peroxidase was used as an indicator for freshness. With hydrogen peroxide and hydroquinone as substrates, the enzymatic reaction of peroxidase produced benzoquinone, which was subsequently reduced on a gold working electrode electrochemically. The progress of the enzymatic reaction could clearly be observed in the change of cyclic voltammograms. Distinct differences were observed in the current change between fresh rice and aged rice, reflecting the remaining activity of peroxide. The current also depended on the time at which rice grains were milled. The result agreed well with those obtained by the conventional fluorometric and guaiacol methods. Comparison of results obtained with different numbers of grains showed that even the measurement with a single grain provided fairly consistent data. Furthermore, the existence of grains of different freshness could be identified using a device with multiple sensing sites.