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Very fine needle-electrode arrays potentially offer both low invasiveness and high spatial resolution of electrophysiological neuronal recordings in vivo. Herein we report the penetrating and recording capabilities of silicon-growth-based three-dimensional microscale-diameter needle-electrodes arrays. The fabricated needles exhibit a circular-cone shape with a 3-μm-diameter tip and a 210-μm length. Due to the microscale diameter, our silicon needles are more flexible than other microfabricated silicon needles with larger diameters. Coating the microscale-needle-tip with platinum black results in an impedance of ~600 kΩ in saline with output/input signal amplitude ratios of more than 90% at 40 Hz-10 kHz. The needles can penetrate into the whisker barrel area of a rat's cerebral cortex, and the action potentials recorded from some neurons exhibit peak-to-peak amplitudes of ~300 μVpp. These results demonstrate the feasibility of in vivo neuronal action potential recordings with a microscale needle-electrode array fabricated using silicon growth technology.

We report here a technique for use in electrical interfaces between neurons and microelectronics, using vertically integrated silicon probe arrays with diameters of 2-3.5 microm and lengths of 60-120 microm. Silicon probe arrays can be fabricated by selective vapor-liquid-solid (VLS) growth. A doped n-type silicon probe with the resistance of 1 k Omega has an electrical impedance of less than 10 M Omega in physiological saline. After inserting the probe arrays into the retina of a carp (Cyrpinus carpio), we conducted electrical recording of neural signals, using the probes to measure light-evoked electrical neural signals. We determined that recorded signals represented local field potentials of the retina (electroretinogram (ERG)). The VLS-probe can provide minimally invasive neural recording/stimulation capabilities at high spatial resolution for fundamental studies of nervous systems. In addition, the probe arrays can be integrated with microelectronics; therefore, these probes make it possible to construct interfaces between neurons and microelectronics in advanced neuroscience applications., ((c) 2010 Elsevier B.V. All rights reserved.)

We report on the development of a microtube electrode array as a neural interface device. To combine the desired properties for the neural interface device, such as low invasiveness with a small needle and a good signal-to-noise ratio in neural recordings, we applied the structure of a glass pipette electrode to each microtube electrode. The device was fabricated as sub-5-microm-diameter out-of-plane silicon dioxide microtube arrays using silicon microneedle templates, which are grown by the selective vapor-liquid-solid method. The microtubes had inner diameters of 1.9-6.4 microm and a length of 25 microm. Impedances ranged from 220 kOmega to 1.55 MOmega, which are less than those for conventional microneedles. In addition, the microtube electrodes had less signal attenuation than conventional microneedle electrodes. We confirmed that the effects of parasitic capacitances between neighboring microtubes and channels were sufficiently small using a test signal. Finally, neural responses evoked from a rat peripheral nerve were recorded in vivo using a microtube electrode to confirm that this type of electrode can be used for both electrophysiological measurements and as a neural interface device.

This paper reports on a fabrication technique for realizing micro-Si probe arrays with MOSFETs on the same Si substrate. Micro-Si probe arrays have been successfully fabricated on Si (111) substrates by selective vapor-liquid-solid (VLS) growth using catalytic Au dot arrays and Si2H6 used as the gas source for a molecular-beam-epitaxy. The Si probes can be grown at temperatures ranging from 500 °C to 700 °C. In this paper, MOSFETs were fabricated on Si (111) substrates and Au dots were placed at the drain regions of the MOSFETs in order to grow the Si probes. VLS growth at 700 °C for 2 h was carried out on these substrates. Consequently, the MOSFETs can be used in Si-chip circuits for the VLS-Si probe array. The electrical characteristics of the MOSFETs were measured before and after the VLS process. After the VLS process, no changes in the MOSFET characteristics were observed due to the effects of Au-diffusion, and the results confirmed that VLS growth at a temperature of 700 °C allows fabrication of micro-Si probes without deterioration of the MOSFETs. VLS-Si probes with controlled conductance were realized. The as-grown `Si probes were of high resistance, but could be changed to various conductivities by impurity diffusion. [ABSTRACT FROM AUTHOR]

Understanding the neural system in the brain requires the detection of signals from the tissue. Microscale electrodes enable high spatiotemporal neural recording, whereas traditional microelectrodes cause material and geometry mismatches between the electrode and the tissue, leading to injury and signal loss during recording. In this study, we propose a fabrication technique that uses magnetic force to facilitate assembly of vertical microscale wire-electrodes on a flexible substrate. Two-channel 15-μm-diameter and 400-μm-length nickel-microwire electrodes on a 5-μm-thick flexible parylene film are designed and fabricated. Impedance characteristics of these electrodes are <500 kΩ at 1 kHz, with output/input signal amplitude ratios of over 90%. In vivo neural recording in mice demonstrates that both local field potentials and action potentials are detected through each wire electrode, confirming the minimal invasiveness during the electrode penetration and through immunohistochemical tissue analysis. [ABSTRACT FROM AUTHOR]

Abstract: In order to record multi-site electroretinogram (ERG) responses in isolated carp retinae, we utilized three-dimensional (3D), extracellular, 3.5-μm-diameter silicon (Si) probe arrays fabricated by the selective vapor–liquid–solid (VLS) growth method. Neural recordings with the Si microprobe exhibit low signal-to-noise (S/N) ratios of recorded responses due to the high-electrical-impedance characteristics of the small recording area at the probe tip. To increase the S/N ratio, we designed and fabricated enlarged gold (Au) tipped Si microprobes (10-μm-diameter Au tip and 3.5-μm-diameter probe body). In addition, we demonstrated that the signal attenuation and phase delay of ERG responses recorded via the Si probe can be compensated by the inverse filtering method. We conclude that the reduction of probe impedance and the compensation of recorded signals are useful approaches to obtain distortion-free recording of neural signals with high-impedance microelectrodes. [ABSTRACT FROM AUTHOR]

• We fabricated a <10-μm diameter coaxial microneedle-electrode. • Applications include multichannel and local-differential neuronal recordings. • LFP and unit-activity were recorded from the mouse's cortex in vivo. • SNR and firing rate were increased by the local-differential recording. Electrophysiological recording requires low invasive electrode geometry in the tissue and high-quality signal acquisitions. Here we propose a <10-μm diameter coaxial cable–inspired needle electrode, which consists of a core electrode in the needle surrounded by another shell electrode. The neuronal recording capability of these electrodes was confirmed by multichannel recording of a mouse cortex in vivo. Given that the shell electrode played the role of a reference electrode, the coaxial electrode also enabled a differential recording at the local area within the tissue. Compared to the recording without the referenced shell electrode, the differential recording demonstrated a twofold higher signal-to-noise ratio, while the firing rate increased. These results suggest that the coaxial microneedle-electrode will provide high-quality neuronal signals in electrophysiological recordings including ex vivo and in vitro applications, similar to the in vivo recording. [ABSTRACT FROM AUTHOR]

• We fabricated a flexible parylene-thread bioprobe and proposed the implantation method based on conventional sewing method. • A device-holding protocol was proposed to enable a stress-free "catch" and "release" of the needle. • EMG signals were recorded from the mouse's MG muscle. • Both the LFP and the spike were recorded from the mouse's visual cortex in in vivo chronic recording. Multichannel recording of the electrical signals from soft biological tissue of brain is an important technique in electrophysiology. However, penetration of conventional rigid needle-electrodes causes physical-stress to the tissue and induces the tissue damage, making the stable recording impossible. The approach reported here involves the use of a flexible "thread-like" device with microelectrodes that enables precise penetration and placement inside the brain tissue, with the help of a guiding microneedle, similar to sewing mechanism. A device-holding protocol, which uses a dissolvable material, is proposed to enable a stress-free "catch" and "release" of the needle. The device is placed in the primary visual cortex (V1) of an in vivo mouse and both the local field potentials (LFP) and the action potentials (spike) are recorded. For over a period of two weeks after device implantation, no remarkable decrease in mouse's weight is observed. Therefore, we conclude that the proposed sewing thread-device enhances the recording of neuronal signals while minimizing the device–induced stress. [ABSTRACT FROM AUTHOR]