Electro-deformation spectroscopy: A unified method for simultaneous electrical and mechanical characterization of single cells

The intrinsic electrical and mechanical properties of cells are not only valuable biophysical markers reflective of physiological conditions but also play important roles in the development and progression of human diseases. Existing single-cell techniques are restricted to assessing either mechanical or electrical properties. We introduce the development of electro-deformation spectroscopy (EDS), namely the frequency-dependent electro-deformation, as a new method for simultaneous electrical and mechanical characterization of individual cells in suspension. To facilitate the practical use of this technology, we developed a testing procedure that evaluates red blood cells (RBCs) directly from whole blood in a simple microfluidic system, employing an electric field magnitude of 34 kV/m over a frequency range of 15 MHz to 100 kHz. The EDS measurement is performed under stationary conditions without special cell stabilization, at a moderate throughput of 50-100 cells per minute. We develop an experimental-computational framework to decouple cell electromechanics by optimizing the most suitable parameters of the relative permittivity of cell membrane, cytoplasm electrical conductivity, and membrane shear modulus. This technique, tested on RBCs from 4 healthy human samples, revealed membrane relative permittivity of 3.6 - 5.8, membrane shear modulus of 2.2 - 2.8 µN/m, and cytoplasm conductivity of 0.47 - 0.81 S/m. EDS analysis identifies the marked intrasample heterogeneity and individual variability in both cellular electrical and mechanical properties. The EDS framework can be readily used to test RBCs across different species, pathological states, and other cell types of similar structures as RBCs. STATEMENT OF SIGNIFICANCE: This work introduces electro-deformation spectroscopy (EDS) as a unified method for simultaneous electrical and mechanical characterization of single cells in suspension. This is the first-of-its-kind technology for such purposes. EDS can be performed in a simple microfluidic system with minimal sample preparation, making it a convenient and powerful tool for label-free, non-invasive single-cell analysis. We validate the applicability of EDS by measuring the intrasample heterogeneity and individual variability based on the electromechanical parameters of interest for human red blood cells. Single-cell EDS has the potential to enable rapid and reliable detection of cellular changes by diseases or drug treatments and provide insights into the fundamental bioelectromechanical mechanisms of cellular adaptation and dysfunction. This work advances the field of single-cell analysis and contributes to the development of biomaterials and biotechnologies based on cellular electromechanics.