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 × 10⁹ 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 × 10⁹ 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 × 10⁹ cells/mL.