Extended Data Fig. 7: Monitoring the change of neuronal membrane potential after attachment of the droplet device.

a, Neuronal membrane potential was measured by confocal imaging using FluoVolt™, a voltage-sensitive fluorescent probe (Methods). Scale bar, 200 μm. b, Frames at various time-points of a zoom-in area in (a) showing the fluorescence change after attachment to a droplet device. Ionic current flowed from top-left to bottom-right of the selected area. Scale bar, 50 μm. c, Relative fluorescence change of individual neurons after attachment of the droplet device. The black curve represents neurons in direct contact with high-salt droplets (0.5 M CaCl₂). The stable fluorescence indicates that the neurons remain in a resting state. The red curve represents neurons under droplet device modulation (see b) and the blue curve represents neurons depolarized by adding 20 mM KCl solution. Three neural microtissues were tested under each condition and five cells from each were randomly selected for fluorescence quantification.