High-density individually addressable platinum nanoelectrodes for biomedical applications

Abstract 3-D vertical nanoelectrode arrays (NEAs) have found applications in several biomedical and sensing applications, including high-resolution neuronal excitation and measurement and single-molecule electrochemical biosensing. There have been several reports on high-density nanoelectrodes in recent years, with the filling ratio of electrodes reaching close to 0.002 (assuming the electrode diameter of 200 nm and pitch of 4 μm). Still, it is well below the nanowire filling ratio required to form interconnected neuronal networks, i.e., more than 0.14 (assuming the electrode diameter of 200 nm and pitch of 1.5 μm). Here, we employ a multi-step, large-area electron beam lithography procedure along with a targeted, focused ion beam based metal deposition technique to realize an individually addressable, 60-channel nanoelectrode chip with a filling ratio as high as 0.16, which is well within the limit required for the formation of interconnected neuronal networks. Moreover, we have designed the NEA chip to be compatible with the commercially available MEA2100-System, which can, in the future, enable the chip to be readily used for obtaining data from individual electrodes. We also perform an in-depth electrochemical impedance spectroscopy characterization to show that the electrochemical behavior and the charge transfer mechanism in the array are significantly influenced by changing the thickness of the SU-8 planarization layer (i.e., the thickness of the exposed platinum surface). In addition to neural signal excitation and measurement, we propose that these NEA chips have the potential for other future applications, such as high-resolution single-molecule level electrochemical and bio-analyte sensing.