Abstract
To advance neuroscience in vivo experiments, it is necessary to probe a high density of neurons in neural networks with single-cell resolution and be able to simultaneously use different techniques, such as electrophysiological recordings and optogenetic intervention, while minimizing brain tissue damage. We first fabricate electrical neural probes with a high density of electrodes and small tip profile (cross section of shank: 47-μm width × 16-μm thickness). Then, with similar substrate and fabrication techniques, we separately fabricate optical neural probes. We finally indicate a fabrication method that may allow integrating the two functionalities into the same device. High-density electrical probes have been fabricated with 64 pads. Interconnections to deliver the signal are 120-nm wide, and the pads are 5 × 25 μm. Separate optical probes with similar shank dimensions with silicon dioxide and silicon nitride ridge single-mode waveguides have also been fabricated. The waveguide core cross section is 250 nm × 160 nm. Light is focused above the waveguide plane in 2.35-μm diameter spots. The actual probes present two output focusing gratings on the shank.
Highlights
One of the main goals of the Brain Research through Advancing Innovative Neurotechnologies (BRAIN) Initiative 1 is to map the brain at the single neuron and synapse level to understand how neural communication drives behavior and affects brain disorders
Michigan neural probes allow the use of micro and nanofabrication techniques and integrate a high density of arrays of sensors
The neural probe is glued on the printed circuit board (PCB) and wire bonded [Fig. 5(a)]
Summary
One of the main goals of the Brain Research through Advancing Innovative Neurotechnologies (BRAIN) Initiative 1 is to map the brain at the single neuron and synapse level to understand how neural communication drives behavior and affects brain disorders. Nanotechnology has opened new pathways to interface single brain cells in vivo in brain tissue due to dimensions comparable to neural cells and the feasibility of integration of different types of sensors. The main element of these type of brain–machine interfaces is a sharp silicon tip (the shank) that is inserted into the animal’s brain and which contains passive or active sensors [electrodes,[3,4] microfluidic channels,[5] optical diffraction gratings,[6] and micro-light-emitting diodes (LEDs)7]. Sensors on the shank are connected, due to metallic interconnections, waveguides, or microfluidic channels, to an extracranial device region having bond pads,[8] optical coupling gratings, or fluidic interfaces.[5] Many in vivo neuroscience studies employ Michigan neural probes to record or stimulate neurons by means of different types of techniques. The shank of such devices can be miniaturized (tip widths larger than 60 μm decrease the quality of recordings)[20] while the sensor density can be increased (to interface simultaneously larger number of neurons).[21]
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