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

We counted bacterial cells ofE. colistrain 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 theE. colicells in the range of c(b)= 0.06 to 1.26 x 10(9) cells/mL. The results showed that forE. coliin 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 x 10(9) cells/mL, whereas the OD, which was independently measured with a spectrophotometer, was only linearly dependent on the concentration of theE. colicells in the range of c(b)= 0.06 to 0.50 x 10(9) cells/mL.