Microneedle devices for intracellular neuronal recording and high throughput cellular interrogation

This dissertation focuses on sub-mum tip microneedle devices for neuronal recording. The first part of this work presents the design and development of an implantable high aspect ratio 350-400 mum tall silicon probe device with flexible interconnects. The probe's ability to penetrate and record from neurons in an isolated brain of the sea slug Tritonia diomedea was tested and it was demonstrated for the first time that an implantable device can record intracellular action potentials. The design features the separation of electronics from the region of cell penetration and hence minimal mechanical load on the cell. The fabrication of the intracellular implant allows for post processing capability after the sharpening of the needle electrode. The success of this prototype is a major step toward self-contained, implantable devices suited for intracellular neuronal recording from freely behaving animals. Enhancements to the working device, in particular needle shaft insulation, tip metallization and reduction of cell wall shear during penetration have been addressed and incorporated into the microfabrication process. Novel biomaterial coatings were evaluated for their suitability as coatings for neural probes. An inherent limitation of this design is that it is not adaptable for multi unit cellular interrogation. The last part of this work presents the technology for low substrate temperature (∼400°C) growth of high-density, defect-free, unidirectional arrays of Si needles using selective vapor-liquid-solid (VLS) mechanism. The low substrate temperature allows possible integration of on-chip CMOS circuitry or biomaterials with minimal thermal damage. The needle growth was performed in a hot wire chemical vapor deposition (HWCVD) chamber that featured the unique combination of a high filament temperature and a low substrate temperature. The needle growth was independent of substrate orientation, enabling possible integration with flexible substrates. The needle arrays (6-8 mum tall, sub-mum tips) are envisioned as high density electrodes of an integrated retinal implant. This work may lead to a "needles on pillars" technology for multi unit intracellular recording from cortical tissue and/or a platform for light stimulation and drug delivery to a network of neurons.