Optocapacitive current of non-thermal origin

Optocapacitive effects are based on sudden jumps in membrane capacitance due to light adsorption. Thus far, photothermal effects are exploited, i.e., in the first step, illumination heats light-absorbing nanoparticles, which transfer the heat to the nearby membrane in the second step [1]. We now propose simplifying the approach by omitting the nanomaterials and using photolipids instead. Their acyl chains undergo a reversible trans-cis photoisomerization due to the photo-susceptibility of the azobenzene moiety. In our hands, the associated capacitance changes of planar lipid bilayers [2] and in HEK cells are large enough to elicit substantial optocapacitive current spikes. The optocapacitive current changes with the (i) surface potential and (ii) the dipole potential of bilayers folded from lipid monolayers of different compositions. Our observation that the sizes of the optocapacitive currents induced by photothermal effects and lipid photoisomerization are comparable paves the way for using photolipids for neuronal stimulation. The work was supported by grants from the FWF (Austrian Science Fund): TAI 181 and the NIH: GM030376. 1. Pinto et al. Biophysical Reviews, 2022. 14(2): p. 569-577. 2. Pfeffermann et al., Journal of Photochemistry and Photobiology B: Biology, 2021: p. 112320.