Bacteria Detection System for Solid Specimen Based on Electrical Measurement

Colony counting method is the most popular method for bacterial assay. The method requires a long incubation time and complex operations based on biological knowledge. Since the assay result is needed as soon as possible in medical and food manufacturing fields, the incubation time is too long for sanitary inspection. Electrical assay methods, such as the dielectrophoretic impedance measurement (DEPIM) method, have been investigated for the fast and easy assay approach. The authors proposed an electrical assay method using impedance measurement in an accompanying paper. However, its accuracy in a low-frequency region should be improved. This paper investigates a method to determine the presence of bacteria by resistance measurement and proposes a practical bacteria detection system that applies a grounding characteristic measurement technique. A parametric measurement unit (PMU) initially developed for semiconductor evaluation is adopted for the measurement. The PMU also works as a D.C. power supply, and a microcomputer controls the PMU. The measured result using the proposed system clearly shows the difference between the presence and absence of Escherichia coli. The result means the system can be used as a speedy and convenient assay method in sanitary inspection.