Fig. 2
Nanoengineered electroporation microelectrodes (NEMs) allow for improved current distribution and electroporation effectiveness by reducing peak potential regions. a Scheme showing the current divider-based electric circuit model with five divisions (“levels”) along a central axis, serving as an equivalent electric circuit model of the newly designed pipette. For simplicity of the scheme, exterior resistances are neglected. b Maximum current density (µA/µm2) of a standard pipette (blue) and an NEM (red) plotted against applied stimulation current (µA). The graph shows that current density of the standard pipette rises twice as quickly when compared to the NEM. c Cross-section of the 3D-FEM model illustrating the total effective electroporation volume and its distribution around the pipette tip at 50 µA employing the NEM (Vm = transmembrane potential). Scale bar = 5 µm. d Cumulated volume of elements for a standard glass pipette (blue) and an NEM (red) beyond a given potential at 50 µA (X-axis, (V) in steps of 0.01 V). e After pulling long-tapered, patch clamp-like pipettes (i), pipettes were successively coated with a thin gold layer (ii) and conductive silver paint (iii). This was necessary to provide efficient grounding of the surface for FIB-assisted milling (iv). f Inside camera view of the vacuum chamber for SEM imaging and FIB-assisted milling. Glass pipettes are mounted and aligned at an angle of 90° relative to the principal axis of the FIB. Gallium ion gun shown in the right upper corner, electron beam mounted vertically in the central portion of the chamber. Scale bar = 5 mm. g Example of an NEM after successful insertion of the five-level hole design, as seen in high-resolution FIB imaging mode. Scale bar = 2 µm
