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

We counted bacterial cells of 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 of the cells in the range of c = 0.06 to 1.26 × 10 cells/mL. The results showed that for in DI water and in PBS, the modelled impedance parameters depend linearly on the concentration of cells in the range of c = 0.06 to 1.26 × 10 cells/mL, whereas the OD, which was independently measured with a spectrophotometer, was only linearly dependent on the concentration of the cells in the range of c = 0.06 to 0.50 × 10 cells/mL.