Akihiro Goryu

Nanoscale sharpening tips of vapor–liquid–solid grown silicon microwire arrays

We developed out-of-plane, high aspect ratio, nanoscale tip silicon microwire arrays for application to penetrating, multisite, nanoscale biological sensors. Silicon microwire arrays selectively grown by gold-catalyzed vapor-liquid-solid growth of silicon can be formed to create sharpened nanotips with a tip diameter of less than 100 nm by utilizing batch-processed silicon chemical etching for only 1-3 min. The tip angles achieved ranged from 11 degrees to 38 degrees. The nanotip silicon microwires can perform gelatin penetration without wire breakdown, indicating their potential penetrating capability for measurements inside biological tissues.

Nanoscale‐Tipped High‐Aspect‐Ratio Vertical Microneedle Electrodes for Intracellular Recordings

Intracellular recording nanoscale electrode devices provide the advantages of a high spatial resolution and high sensitivity. However, the length of nanowire/nanotube-based nanoelectrodes is currently limited to <10 μm long due to fabrication issues for high-aspect-ratio nanoelectrodes. The concept reported here can address the technological limitations by fabricating >100 μm long nanoscale-tipped electrodes, which show intracellular recording capability.

Vertically integrated metal-clad/silicon dioxide-shell microtube arrays for high-spatial-resolution light stimuli in saline

Microdevices composed of integrated microscale light source arrays are powerful tools in optogenetic applications. Herein, we prepared vertically aligned 3-μm inner diameter silicon dioxide (SiO2) tube-based optical light waveguide arrays. To increase the locality of the light stimuli through the tube, we also fabricated metal-cladded SiO2 tubes using iridium (Ir). After filling the tube with a saline solution, the saline-core/Ir-clad/SiO2-shell waveguide exhibited light stimuli without spreading. With a 532-nm wavelength, the half-power width of the light intensity measured 10 μm above the tube tip was 3 μm, while that of the saline/SiO2-shell waveguide was 9.6 μm, which was more than three times wider. Such high-spatial-resolution optical light stimuli will offer a new class of optogenetic applications, including light stimuli for specific regions of a neuron (e.g., axons or dendrites).

A vertical micro-scale light guiding silicon dioxide tube array for optical neurostimulator

In this paper, we present out-of-plane micro-scale diameter light guiding silicon dioxide tube arrays for use in optical stimulation of neurons. An optical propagation through the dioxide tube was calculated by using finite-difference time-domain (FDTD) simulation. Based on the calculated result, we designed and fabricated 3-µm-inner diameter 24-µm-height silicon dioxide tube arrays with the wall thickness of 0.5 µm, using selective vapor-liquid-solid (VLS) growth of silicon microwire, followed by microfabricating processes. The optical transmission capability of the fabricated tube was experimentally confirmed by using light of 470 nm, 525 nm, and 595 nm in wavelength.

A vertically integrated nanoscale tipped microprobe intracellular electrode array

Here we report integration of nanoscale tipped 120-μm-long vertical microprobe electrode (NTE) array and intracellular recordings using a gastrocnemius muscle of a mouse. The tip diameter and curvature radius of the NTE was <; 200 nm, respectively, and the controlled height of the exposed tip section was 4 μm. The impedance of the fabricated NTE exhibited 3.1 MΩ at 1 kHz in saline, with the output/input signal amplitude ratio of 50%. The penetrated NTE into the muscle of a mouse detected the resting membrane potentials with the amplitude of ~ -200 mV, indicating that the NTE device detected intracellular signals from the mouses muscle. Although we have demonstrated the intracellular recording capability using a muscle, such nanoscale electrodes with a high aspect ratio can be used for multisite intracellular recordings within numerous neuronal tissues including brain slice.

Integration and 3D fabrication techniques to nanoscale-tip silicon high-aspect-ratio microprobe arrays

We developed integration and three-dimensional (3D)-fabrication techniques to nanoscale-tip silicon-microprobe arrays for multiple electrical nano-measurement systems with a high aspect ratio. Vapor-liquid-solid (VLS) grown vertically-aligned 120µm-length silicon microprobe arrays (2µm-diameter), each with nanoscale-tip by controlling the silicon-etching (less than 100-nm-diameter, radius of curvature 50nm), have been integrated with IC-processed interconnections. Subsequently, the nanotip silicon probe is entirely covered with Pt/Ti and encapsulated with an insulator, SiO2. In addition, herein we proposed the use of a spray-coating of photoresist and cycled etchings of the photoresist/SiO2 at the probe-tips. Consequently, the nanotips can precisely be patterned and etched, resulting in the exposed Pt/Ti/silicon-nanotip with a controlled height of 2µm.

Batch Fabrication of Out-of-Plane, IC-Compatible, Nanoscale-Tip Silicon Neuroprobe Arrays

We developed a batch-fabrication of nanoscale-tip silicon microprobe arrays for use in multipoint nanoscale investigations of cell/neuron in-vivo/in-vitro. Sharpened tips, less than 100nm diameter, can be formed at the tips of out-of-plane three-dimensional silicon microprobe (length ≫10¿m) arrays, by silicon wet etching-based batch-process within only 1-3min, providing precisely controlled tip angles ranging from 15° to 50°. The penetration capability of the nanoscale-tip microprobes was demonstrated, using finite element modeling (FEM) simulations and penetration tests with a gelatin as tissue/cell.

Metal/silicon dioxide microtube improves optical and electrical properties of neuroprobe

Here we report vertical metal/silicon dioxide (SiO2) multiwalled microtube arrays as electrical and optical neuroprobes for “optogenetic”. Three-dimensional metal/SiO2-microtube arrays can be fabricated by vapor-liquid-solid (VLS) growth of silicon-wire, followed by the SiO2/metal depositions and the core-silicon etching. As the inside metal, we use iridium (Ir) with a low electrical electrolyte/electrode interfacial impedance in saline. An optical propagation through the Ir/SiO2-tube calculated by finite-difference time-domain (FDTD) method clearly indicates the effect of the inside Ir on the improved locality of light stimuli with the spot diameter of <; 3 μm. These results suggest that the Ir/SiO2-microtube array provides the low-impedance electrode and local optical stimuli with a same alignment, promising a new class of multifunctional neuroprobes for optogenetic.

Electrical catching and transfer of nanoparticles via nanotip silicon probe arrays

We demonstrated batch, pinpoint, and multisite-transfer of nanoparticles via vertically-aligned nanotip silicon probe arrays for powerful applications of nanoinjectors, including local drug delivery and DNA transfer into biological samples (e.g., cell, neuron and tissue). Although several nanoinjections have been demonstrated using “nanoprobe” (e.g., glass pipette, silicon nanowire and carbon nanotube [1–3]), the common issues of these devices are the limitation of the probe number, short length and robustness of the probe section. In order to solve these issues, we propose a nanoinjector, based on a vertical nanotip probe array with a high aspect ratio. Here, we demonstrated electrical batch trappings of nanoparticles at positive biased nanotips, and the trapped nanoparticles were released by ultrasonic vibration. These preliminary results indicate the nanoparticle transfer capability of the nanotip probes for use in multisite deep nanoinjections on numerous biological samples.