Nanowire electrodes for high-density stimulation and measurement of neural circuits

Abstract

Brain-machine interfaces (BMIs) that can precisely monitor and control neural activity will likely require new hardware with improved resolution and specificity. New nanofabricated electrodes with feature sizes and densities comparable to neural circuits may lead to such improvements. In this perspective, we review the recent development of vertical nanowire (NW) electrodes that could provide highly parallel single-cell recording and stimulation for future BMIs. We compare the advantages of these devices and discuss some of the technical challenges that must be overcome for this technology to become a platform for next-generation closed-loop BMIs.

Keywords: brain machine interface (BMI); electrophysiology; nanotechnology; nanowires; neuroengineering.

Figure 1

NWs as intracellular electrodes. (A) The electrode diameters for various methods to record and stimulate neural activity. Electrodes with diameters less than 1 micron can be used as intracellular probes. Photo credits: DBS—EPDA.com, Microelectrodes—microsystems.utah.edu. (B) Equivalent circuit model for a cell on top of an extracellular (left) and intracellular (right) electrode. The membrane resistance, capacitance, and Nernst potential is shown as R_m, C_m, and E_m, respectively. The voltage recorded extracellularly (V_ex) is proportional to I_m, and typically has a magnitude of 0.4 mV for a neuronal action potential. The voltage recorded intracellularly (V_in), however, is proportional to V_m, and typically has a magnitude of greater than 10 mV for a neuronal action potential. (C) Optical microscope image of a rat cortical neuron grown on top of a vertical NW electrode, scale bar 10 microns. (D) Scanning electron micrograph of a set of vertical NWs, scale bar 1 micron. [(C) and (D) adapted from Robinson et al. (2012)].

Figure 2

Intracellular recording methods. (A) Whole cell patch pipette configuration measures a voltage (V_pipette) proportional to the membrane potential (V_m). (B) A vertical glass nanotube (blue) is grown on top of an FET (pink) that lies within an insulated NW (gray). When the nanotube penetrates the cellular membrane, the membrane potential can be measured as a change in the source-drain current (I_SD). (C) A platinum NW (red) is deposited on top of a platinum electrode (red) that is insulated by silicon nitride (blue). The voltage recorded at the NW (V_NW) is then proportional to the membrane potential. (D) A silicon NW (gray) insulated by glass (blue) is capped with a metallic film such as platinum (red). Similarly to (C), V_NW is proportional to V_m, however in this configuration the NW sidewalls are insulated by glass, improving the amplitude of the measured signal and proving a surface for cell membrane fusion.