Double interdigitated array microelectrode-based impedance biosensor for detection of viable Escherichia coli O157:H7 in growth medium

Double interdigitated array microelectrodes (IAM)-based flow cell was developed for an impedance biosensor to detect viable Escherichia coli O157:H7 cells after enrichment in a growth medium. This study was aimed at the design of a simple flow cell with embedded IAM which does not require complex microfabrication techniques and can be used repeatedly with a simple assembly/disassembly step. The flow cell was also unique in having two IAM chips on both top and bottom surfaces of the flow cell, which enhances the sensitivity of the impedance measurement. E. coli O157:H7 cells were grown in a low conductivity yeast–peptone–lactose–TMAO (YPLT) medium outside the flow cell. After bacterial growth, impedance was measured inside the flow cell. Equivalent circuit analysis indicated that the impedance change caused by bacterial growth was due to double layer capacitance and bulk medium resistance. Both parameters were a function of ionic concentration in the medium, which increased during bacterial growth due to the conversion of weakly charged substances present in the medium into highly charged ions. The impedance biosensor successfully detected E. coli O157:H7 in a range from 8.0 to 8.2 × 108 CFU mL−1 after an enrichment growth of 14.7 and 0.8 h, respectively. A logarithmic linear relationship between detection time (TD) in h and initial cell concentration (N0) in CFU mL−1 was TD = −1.73 log N0 + 14.62, with R2 = 0.93. Double IAM-based flow cell was more sensitive than single IAM-based flow cell in the detection of E. coli O157:H7 with 37–61% more impedance change for the frequency from 10 Hz to 1 MHz. The double IAM-based flow cell can be used to design a simple impedance biosensor for the sensitive detection of bacterial growth and their metabolites.