Towards Bacteria Counting in DI Water of Several Microliters or Growing Suspension Using Impedance Biochips

We counted bacterial cells of E. coli strain K12 in several-microliter DI water or in several-microliter PBS in the low optical density (OD) range (OD = 0.05–1.08) in contact with the surface of Si-based impedance biochips with ring electrodes by impedance measurements. The multiparameter fit of the impedance data allowed calibration of the impedance data with the concentration c(b) of the E. coli cells in the range of c(b) = 0.06 to 1.26 × 10(9) cells/mL. The results showed that for E. coli in DI water and in PBS, the modelled impedance parameters depend linearly on the concentration of cells in the range of c(b) = 0.06 to 1.26 × 10(9) cells/mL, whereas the OD, which was independently measured with a spectrophotometer, was only linearly dependent on the concentration of the E. coli cells in the range of c(b) = 0.06 to 0.50 × 10(9) cells/mL.