Individually Addressable Nanowire Arrays for Probing Neuronal Culture and Tissue
Nanowire electrode arrays are widely used to probe neuronal and cardiomyocyte’s activities and are promising to bridge the gap between the standard gold technology of patch clamp and commercial microelectrode array to realize the large-scale intracellular recording with high signal-to-noise ratio. It is challenging to fabricate nanowire array to maintain both penetration ability for less invasiveness to the cell and biomechanical stability at the cell-nanowire interface for long term recording. In addition to the challenge of obtaining an ultra-sharp nanowire tip, current nanowire arrays are constrained with their height and the presence of a number of extracellular nanowires, which limit their intracellular ability. Additionally, the intracellular recording mechanisms rely on electroporation which damages the cell membrane, leads to instability in the recording and prevents achieving long term recording ability. The objectives of this thesis, described in five chapters, are to develop individually addressable, ultra-sharp tip, high density, high-yield nanowire arrays to probe large neuronal network and cardiac tissues. Our platform will pave the way for longitudinal electrophysiological experiments on synaptic activity in human iPSC-based disease models of neuronal networks, critical for understanding the mechanisms of neurological diseases and for developing drugs to treat them.
In the second chapter, we created an individually electrically addressable, scalable, non-destructive, highly doped Si nanowire array for probing primary rodent and human stem cell derived neurons. The nanowire array has superior spatial resolution down to submicrometer site-to-site spacing and permits natural penetration into neuronal membranes. We developed an electrical model and deconvoluted the recorded potentials that resulted in millisecond wide action potentials that had similar properties to those measured by patch clamp. We validated the intracellular nature of nanowire-neuron interface by cross-sectional FIB/TEM. The neurons on nanowires were pharmacologically responsive: the activity increased with adding KCl and inhibited once adding TTX.
In the third chapter, we developed a high yield (100%) method for fabrication of nanowires array with ultra-sharp tip (a few tens of nanometer) based on Si substrate. The height, diameter, and pitch of nanowires are adjustable. The tip materials are flexible to change to any bio-materials, such as Au, Pt, Ag/AgCl, PEDOT-PSS. Surface roughness and materials are adjustable for better cell-attachment and neurite growth. Electrophysiological recordings from mouse primary neurons revealed high signal to noise ratios with clear excitatory postsynaptic potential (EPSP) detection preceding action potentials. We recorded spike trains of action potentials from large neuronal network. Our ultra-shape nanowire array recorded neurons’ clear responses to electrical stimulation and pharmacological drugs. The interfaces of neurons and nanowires were characterized by SEM/FIB demonstrating that the nanowires penetrated the neuronal membranes. Cardiac tissue activity was also recorded and showed pacemaker action potentials.
In the fourth chapter, we integrated Pt nanowires with bidirectional CMOS integrated circuits. Two methods were optimized for Pt nanowire integration by Focus Ion Beam. Rat cortical neurons were cultured and recorded. It was pharmacologically responsive to KCl and TTX, which indicated the stable nanowire-neuron interface.
In the fifth chapter, ongoing projects are introduced with regarding to the scalability to 1024 channel arrays, high density depth probe devices, large scale integration of nanowires with CMOS chip and electrofluidic neuronal interfaces.