Speaker
Description
Dielectric properties of cells are central to life science research and label-free diagnostics. Microfabrication now enables single-cell electrical measurements, but existing platforms face a trade-off: trapped-cell systems offer high frequency resolution with low throughput, while flow-based systems provide high throughput with limited frequency resolution.
Building on recent work by Morgan’s group (ACS Sensors, 5(2), 423–430, 2020; Lab Chip, 25(12), 2939–2948), we present a novel microfluidic impedance cytometry platform capable of rapid dielectric characterization of flowing cells at 14 simultaneous, logarithmically spaced frequencies between 250 kHz and 50 MHz, achieving an unprecedented resolution of 6.1 data points per decade. We validate the approach on red blood cells (RBCs) and yeast cells, both under native conditions and under chemical or physical stress. Specifically, in the case of RBCs we investigate the exposure to two antimicrobial peptides (i.e., 1 µM DNS-PMAP23 and 20 µM trichogin GA IV), whereas for yeast cells we consider prolonged exposure to high temperature (i.e., 30 minutes at 70°C).
Individual flowing cells pass through the sensing region of the microfluidic chip, which comprises two measurement zones. Each measurement zone uses a standard differential wiring scheme and is connected to a lock-in amplifier. The two lock-in amplifiers use distinct frequency sets to characterize cell impedance and operate in a synchronized mode. For each measured cell, the impedance traces acquired from the two measurement zones are combined and processed by a tailored algorithm to obtain the experimental impedance spectrum. This experimental spectrum is then fitted with an appropriate shell model to obtain the cell dielectric properties.
Significant changes in the dielectric spectra of treated versus native RBCs were observed, which translate into different values of the dielectric properties estimated via model fitting. Control RBCs are characterized by (median values): 2.7 µm radius, 0.95 µF/cm2 membrane capacitance, and 0.41 S/m cytoplasm conductivity. Incubation with DNS-PMAP23 and with trichogin GA IV is associated with larger (3.1 µm) and smaller (1.9 µm) median radius, respectively. Both peptides induce a reduction in membrane capacitance and an increase in cytoplasm conductivity. For the yeast cells, while the control sample exhibits a typical relaxation behavior, the spectrum of the heat-treated cells remains almost constant across the probed frequency range. In fact, heating induces coagulation of intracellular content with consequent decrease of intracellular conductivity.
We believe that the developed technology, overcoming the longstanding trade-off between high throughput and high frequency resolution, will accelerate novel discoveries in the field of single cell electrical characterization and associated applications in diagnostics and life science.