Relating membrane potential to impedance spectroscopy

Non-invasive, label-free assessment of membrane potential of living cells is still a challenging task. The theory linking membrane potential to the low frequency α dispersion exhibited by suspensions of spherical shelled particles (presenting a net charge distribution on the inner side of the shell) has been pioneered in our previous studies with emphasis on the permittivity spectra. Whereas α dispersion is related to a rather large variation exhibited by the permittivity spectrum, we report that the related decrement presented by the impedance magnitude spectrum is either extremely small, or occurs (for large cells) at very small frequencies (~mHz) explaining the lack of experimental bioimpedance data on the matter. We stress that appropriate choice of the parameters (as revealed by the microscopic model) may enable access to membrane potential as well as to other relevant parameters when investigating living cells and charged lipid vesicles. We analyse the effect on the low frequency of the permittivity and impedance spectra of: I. Parameters pertaining to cell membrane i.e. (i) membrane potential (through the amount of the net charge on the inner side of the membrane), (ii) size of the cells/vesicles, (iii) conductivity of the membrane; II. Parameters of the extra cellular medium (viscosity and conductivity). The applicability of the study has far reaching implications for basic (life) sciences (providing non-invasive access to the dynamics of relevant cell parameters) as well as for biosensing applications, e.g. assessment of cytotoxicity of a wide range of stimuli.