Abstract
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 cb of the E. coli cells in the range of cb = 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 cb = 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 cb = 0.06 to 0.50 × 109 cells/mL.
Highlights
The techniques used to count biological species can be categorized into physical and biological ones
An example, imperfect and resistance are associated with space charge polarization regions and with adsorption of coli in the semicircle is correlated with constant phase elements (CPE) [20]
The impedance changes of PS and BS biochips were studied under the same experimental conditions without any analyte in the area inside the top of the ring electrode, shown as black thick curves in Figure 5
Summary
The techniques used to count biological species can be categorized into physical and biological ones. To assess the exact number and species of bacteria in a suspension, the biological method of plate counting agar (PCA) [5] is used, which involves plating of serial dilutions of the relevant sample and counting the growing colonies on the day. This method is very labor-intensive and time-consuming, giving results only after approximately 24 h. We counted heat-inactivated E. coli cells using impedance biochips in DI water or PBS by subsequently adding a small amount of sample solution to the chips filled with 20 μL of solvent. The impedance change of the impedance biochips was measured, modeled, and correlated with the concentration of E. coli in the suspension
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