Differentiation of live and heat-killed E. coli by microwave impedance spectroscopy

Abstract

The detection of bacteria cells and their viability in food, water and clinical samples is critical to bioscience research and biomedical practice. In this work, we present a microfluidic device encapsulating a coplanar waveguide for differentiation of live and heat-killed E.scherichiacoli cells suspended in culture media using microwave signals over the frequency range of 0.5 GHz-20 GHz. From small populations of ∼15 E. coli cells, both the transmitted (|S21|) and reflected (|S11|) microwave signals show a difference between live and dead populations, with the difference especially significant for |S21| below 10 GHz. Analysis based on an equivalent circuit suggests that the difference is due to a reduction of the cytoplasm conductance and permittivity upon cell death. The electrical measurement is confirmed by off-chip biochemical analysis: the conductivity of cell lysate from heat-killed E. coli is 8.22% lower than that from viable cells. Furthermore, protein diffusivity increases in the cytoplasm of dead cells, suggesting the loss of cytoplasmic compactness. These changes are results of intact cell membrane of live cells acting as a semipermeable barrier, within which ion concentration and macromolecule species are tightly regulated. On the other hand, the cell membrane of dead cells is compromised, allowing ions and molecules to leak out of the cytoplasm. The loss of cytoplasmic content as well as membrane integrity areis measurable by microwave impedance sensors. Since our approach allows detection of bacterial viability in the native growth environment, it is a promising strategy for rapid point-of-care diagnostics of microorganisms as well as sensing biological agents in bioterrorism and food safety threats.

Thermal Shock Response of Yeast Cells Characterised by Dielectrophoresis Force Measurement

“…These measures are to be considered because despite electroporation is an entirely distinct technique from heat treatment, its outcome over the structure of the cell membrane is almost the same that the one reached through heat treatment. In fact, because they both have the same effect over the cell’s structure, they both explain the increase in cell membrane conductivity through the same principle [41].…”

“…In particular, it has been applied to discern between cells damaged by heat treatment and the alive ones [33]. Admittedly, other approaches have been employed to the same problem [41], though none of them to yeast cells. Consequently, finding yeast cell discrimination methods applicable to determine biological cell parameters, in this case, the damage caused by heating, reveals itself as an objective worth pursuing.…”

Broadband Electrical Sensing of a Live Biological Cell with In Situ Single-Connection Calibration

“…Traditional broadband electrical sensing techniques [ 3 , 4 , 5 ] typically use uniform transmission lines as calibration standards before sensing unknown liquids or randomly located cells [ 1 , 11 ]. However, they are not suitable for sensing a precisely located cell.…”

Real‐time monitoring of Escherichia coli concentration with planar microwave resonator sensor

“…The conjunction of microwave electromagnetics and microfluidic technology is starting to be utilized in cancer‐cell identification, and bacterial and viral contamination monitoring . A coplanar waveguide integrated with a microfluidic structure has been reported to distinguish live from heat‐killed E. coli cells with OD 600 of 3.0 (2.4 × 10 9 cells/mL) at a wide range of frequency (0.5‐20 GHz) …”

“…[16][17][18] A coplanar waveguide integrated with a microfluidic structure has been reported to distinguish live from heat-killed E. coli cells with OD 600 of 3.0 (2.4 × 10 9 cells/mL) at a wide range of frequency (0.5-20 GHz). 19 Microwave-microfluidic biosensors enable label-free, real-time, and sensitive characterization of biological cells in an efficient and high-throughput fashion, which could be critical to the clinical anaylsis. This work presents a planar open-loop ring resonator integrated with microfluidics for the detection of E. coli bacteria concentration in growth media solution with an initial OD 600 value of 1.2.…”