Microwave dielectric spectroscopy of alive single human cells
Résumé
Dielectric spectroscopy is a powerful technique for non-ionizing and non-destructive material characterization. Therefore, its development for the analysis of living cells is very attractive for biological researches and biomedical applications, where non-invasivity, label-free and contact-less abilities as well as in-liquid measurements constitute important leitmotivs. Additionnaly, the investigation of the microwave band for dielectric spectroscopy enables the measurements of living cells directly into their culture medium, without tremendous losses induced by the rich ionic and nutrients content of the surrounding fluid [1]. This ability should be considered in complementarity to the electromagnetic field penetration beyond the capacitive bi-lipid cytoplasmic membrane of cells in this frequency range and consequently confers a strong interest to develop and evaluate microwave dielectric spectroscopy for cellular analysis. Demonstrations of microwave dielectric spectroscopy have been performed with cells suspensions [1] and also at the single cell level in different measurement conditions [2-4]. In our developments, we have developed a microwave based sensor able to trap a single cell surrounded by its culture medium (traditional RMPI medium with 10% of Foetal Calf Serum) [5]. In this paper, we focus on the broadband capacitive and conductive contrasts from 40 MHz to 40 GHz, which have been successfully measured on several individual living and dead cancer cells (THP1 cell lines). Microwave dielectric spectroscopy of single cells confirms the results previously obtained for cells suspensions [6]. Dead cells present indeed an increased capacitive contrast compared to living ones, induced by the equilibrium between intra and extracellular media, due to the permeabilization of the plasma membrane. This result is corroborated by the real time monitoring of a chemically induced cell death with microwave dielectric spectroscopy, performed at the single cell level. It not only enables to extract dielectric spectra of the same single cell in its two pathological states, alive and dead, but it also provides the death kinetic of the single cell submitted to a specific chemical and its associated dose. It opens the door toward dielectric kinetic investigations of chemical impacts on single cells, with potential applications in personalized medicine.