The interface between biological and semiconductor systems gains increasing attention of scientists and engineers as more advanced fabrication techniques in nanotechnology allow for tailor-made nanodevices. Here, applications are found in arising interdisciplinary research fields such as medicine and bioengineering for drug delivery, stimulation, and sensing. In addition to the functionality of the nanoscale device itself, the controlled interaction of the nanoscale device with the biological system is an important requirement for successful implementation. Particularly, the nature of the contact area between electrode and cell membrane plays a crucial role to maximize signal strength and to reduce noise by leakage currents in electrical junctions between nanoelectronics and neurological tissue. Tweaking the electrode’s surface by vertically aligned nanowires appears to be a promising approach to enhance the aforementioned properties since the contact area is maximized and current leakage can be minimized by limiting electrical contact to the nanowire tips. In this study, we interfaced human stem cells with such vertically aligned nanowires with various nanowire lengths, diameters, and array pitches. We determined different wrapping regimes of the cell’s membrane around the nanowires depending on the growth parameter set and tested the electrophysiological properties by patch clamping. In particular, we varied the nanowire lengths and the array pitches from the sub-micron range to several microns and used diameters thinner than 100 nm up to hundreds of nanometers. The wires were fabricated in a bottom-up approach by Ga droplet-assisted growth of GaAs on <111> P-doped Si wafers. The array pitch was controlled by pre-patterning a 15 nm layer of thermal SiO2 on the wafer by electron beam lithography. The lengths were defined by growth time catalyzed by the Ga droplet, whereas the diameter was increased with further growth without Ga droplet.
In summary, we found complete wrapping of the membrane around the nanowires --enforced by short nanowires, small diameters, and large array pitches-- as well as cells suspended on nanowire tips like tiny fakirs favored by long nanowires, large diameters, and small array pitches. In general, our results are in accordance with the predicted regimes by the model from N. Buch-Månson et al. (Adv. Funct. Mater. 2015, 25, 3246–3255) and allow for choosing a set of parameters aiming for a specific interaction regime.