Bacterial Concentration Detection using a PCB-based Contactless Conductivity Sensor

Abstract

Capacitively coupled contactless conductivity detection (C4D) is an improved approach to avoid the problems of labor-intensive, time-consuming and insufficient accuracy of plate count as well as the high-cost apparatus of flow cytometry (FCM) in bacterial counting. This article describes a novel electrode-integrated printed-circuit-board (PCB)-based C4D device, which supports the simple and safe exchange of capillaries and improves the sensitivity and repeatability of the contactless detection. Furthermore, no syringe pump is needed in the detection, it reduces the system size, and, more importantly, avoids the effect on the bacteria due to high pressure. The recovered bacteria after C4D detection at excitation of 25 Vpp and 60–120 kHz were analyzed by flow cytometry, and a survival rate higher than 96% was given. It was verified that C4D detection did not influence the bacterial viability. Moreover, bacteria concentrations from 106 cells/mL to 108 cells/mL were measured in a linear range, and relative standard deviation (RSD) is below 0.2%. In addition, the effects on bacteria and C4D from background solutions were discussed. In contrast to common methods used in most laboratories, this method may provide a simple solution to in situ detection of bacterial cultures.

How Geometry Affects Sensitivity of a Differential Transformer for Contactless Characterization of Liquids

“…By plotting Equation ( 7) versus the ratio r P,M /δ S , Figure 5 is obtained, where r P,M /δ S can be varied by changing the primary coil radius r P,M and the standard depth of penetration δ S depending on the sample conductivity and the excitation frequency according to Equation (5).…”

“…Calculating the true depth of penetration δ T for the differential transformer used here with r P,M = 9.55 mm and d 0 = 11.25 mm, Equation ( 9) results in δ T = 7 mm, which is significantly lower than the δ S of approximately 1 m due to the relatively low conductivity of the medium κ (e.g., blood) and excitation frequency f according to Equation (5).…”

“…Nevertheless, due to the small cross-section of the capillary, C 4 D is not suitable for in-line measurements where higher fluxes of the medium is expected. In addition, due to the above-mentioned poor penetration properties of the electric field through the capillary, the capillary wall can have a dominant influence on the impedance in this principle depending on the conductivity of the sample solution [5].…”

Editorial for the Special Issue on Microfluidics for Cells and Other Organisms

“…By adding “organisms” to the volume title, I was hoping for manuscripts beyond just cells. So, it was good to see that there were submissions of papers on zebrafish [1] and bacteria [2]. This volume highlights a diverse collection of research on single cell manipulation, diagnostics, cell migration, cell flow cytometry, to name a few.…”

“…I see this as a positive development of more portable devices, which can be deployed remotely to, for example, perform diagnostics. Zhang et al [2] used conductivity to measure the concentration of bacteria.…”