Fig. 1
Effectiveness of standard glass microelectrode electroporation can be predicted by FEM but is restricted in practice by physical limitations. a 3D-FEM model showing the center cut of a standard glass micropipette. The figure illustrates the volume where effective electroporation (transmembrane potential >200 mV) can occur at 1 µA (Vm = transmembrane potential). Inset depicting a twofold magnification of the effective electroporation zone close to the pipette tip. Scale bar = 1 µm. b Plot of corresponding voltage drop along the first micrometer of the central axis of the pipette at 1 µA. Black rings indicate individual elements along the central axis of the pipette (assumed electroporation threshold of 200 mV marked by the dashed red horizontal line; resulting critical distance of 0.285 µm indicated by the dashed red vertical line). c Center cut of the 3D-FEM model employing a standard glass micropipette at 100 µA, illustrating the volume where effective electroporation (transmembrane potential >200 mV) can occur. Scale bar = 5 µm. d Corresponding voltage drop along the first 40 µm of the central axis of the pipette at 100 µA. Black rings indicate individual elements along the central axis of the pipette. Electroporation threshold and critical distance (~22 µm) as in b. e When increasing stimulus intensities beyond 30–40 µA, a jet-like convection movement and gas bubble (black arrow) formation appear, as seen here in an exemplary camera frame under the x20 objective. Scale bar = 20 µm. f Current threshold values (µA) for the jet (red) and gas bubble (blue) phenomenon plotted against tip radius (µm). Dashed lines indicating a linear fit for both (R2 = 0.58 for jet, red and R2 = 0.74 for bubble, blue)
