Yu-Tao Lee

Flexible carbon nanotubes electrode for neural recording.

This paper demonstrates a novel flexible carbon nanotubes (CNTs) electrode array for neural recording. In this device, the CNTs electrode arrays are partially embedded into the flexible Parylene-C film using a batch microfabrication process. Through this fabrication process, the CNTs can be exposed to increase the total sensing area of an electrode. Thus, the flexible CNTs electrode of low impedance is realized. In application, the flexible CNTs electrode has been employed to record the neural signal of a crayfish nerve cord for in vitro recording. The measurements demonstrate the superior performance of the presented flexible CNTs electrode with low impedance (11.07 kohms at 1 kHz) and high peak-to-peak amplitude action potential (about 410 microV). In addition, the signal-to-noise ratio (SNR) of the presented flexible CNTs electrode is about 257, whereas the SNR of the reference (a pair of Teflon-coated silver wires) is only 79. The simultaneous recording of the flexible CNTs electrode array is also demonstrated. Moreover, the flexible CNTs electrode has been employed to successfully record the spontaneous spikes from the crayfish nerve cord. The amplitude of the spontaneous peak-to-peak response is about 25 microV.

An active, flexible carbon nanotube microelectrode array for recording electrocorticograms

A variety of microelectrode arrays (MEAs) has been developed for monitoring intra-cortical neural activity at a high spatio-temporal resolution, opening a promising future for brain research and neural prostheses. However, most MEAs are based on metal electrodes on rigid substrates, and the intra-cortical implantation normally causes neural damage and immune responses that impede long-term recordings. This communication presents a flexible, carbon-nanotube MEA (CMEA) with integrated circuitry. The flexibility allows the electrodes to fit on the irregular surface of the brain to record electrocorticograms in a less invasive way. Carbon nanotubes (CNTs) further improve both the electrode impedance and the charge-transfer capacity by more than six times. Moreover, the CNTs are grown on the polyimide substrate directly to improve the adhesion to the substrate. With the integrated recording circuitry, the flexible CMEA is proved capable of recording the neural activity of crayfish in vitro, as well as the electrocorticogram of a rat cortex in vivo, with an improved signal-to-noise ratio. Therefore, the proposed CMEA can be employed as a less-invasive, biocompatible and reliable neuro-electronic interface for long-term usage.

Flexible UV-Ozone-Modified Carbon Nanotube Electrodes for Neuronal Recording

Adv. Mater. 2010, 22, 2177–2181 2010 WILEY-VCH Verlag G Neurophysiologists have used sharpened metal electrodes to electrically stimulate neuronal activities to investigate the physiological functions of the brain. Moreover, they employed this electrical stimulation to treat diseases such as Parkinson’s disease, dystonia, and chronic pain. As neurons utilize electrical potential difference between their cell membranes to transmit electrical signals, this particular way of communication enables us to record the neuronal activity extracellularly or intracellularly. For the extracellular recording approach, the electrodes are positioned intimately next to neuron cells to record and to stimulate their electrical activity by capacitive coupling. The coupling efficacy of these electrical recordings or interventions depends significantly on the selectivity, sensitivity, charge-transfer characteristics, long-term chemical stability, and interfacial impedance between electrodes and target tissue. The most common approach to further investigate the functional behavior of neurons, is using Si-based multimicroelectrode probes fabricated by the micro-electromechanical system (MEMS) method to replace the conventional electrodes (Ag/AgCl) in the aspect of device-structure improvement and scaling down device sizes. However, Si-based MEMS electrodes are extremely rigid and cannot be deformed inside the organs; therefore, the recorded positions are easily shifted and the target tissues are consequently damaged when the animals are in motion. This will become an obstacle in future long-term implantation and real-time recording applications. An alternative method is the use of flexible electrodes presented by several groups. The authors utilized soft materials, such as poly(dimethylsiloxane), SU-8 epoxy-based negative photoresist, and polyimides, to fabricate microelectrodes that can deform while being attached to the tissues and that can also be fabricated into small-scale devices using MEMS methods. Not only would rigid Si-based MEMS probes damage target tissues, the reduced electrode size also resulted in a significantly increase in impedance that may degrade recording sensitivity and limit the stimulating current deliverable through an electrode. In order to resolve above issues, the impedance of the electrodemust be as low as possible. Carbon nanotubes (CNTs) exhibit intrinsically large surface areas (700–1000m g ), high electrical conductivity, and intriguing physicochemical properties. Most importantly, CNTs are chemically inert and biocompatible. Based on the above, the promising advantages of flexible substrates and CNTs lead the attempt of fabricating CNTs directly on flexible substrates as microelectrodes for neuronal recording. In this work, the feasibilities of growing CNTs on flexible polyimide substrates at low temperatures (400 8C) by catalyst-assisted chemical vapor deposition (CVD) and utilizing the above devices (see the schematic image in Fig. 1a and the photo in Fig. 1b) as electrodes for extracellularly neuronal recording were investigated. The electrical enhancement (by UV-ozone exposure), biocompatibility (by neuron cell cultures), long-term usage and adhesion, and the detection of action-potential signals on crayfish (using flexible UV-ozone-modified CNTelectrodes) were examined. After a series of process optimizations, the 5-nm Ni-catalyst layer and C2H2 (60 sccm)/H2 (10 sccm) process gases at 5 Torr were found to be the optimum CNT growth parameters in this work. Besides, the Au layer could facilitate CNTgrowth. Figure 1c shows that CNTs have been grown on the polyimide substrate with Au layer, while not on that without Au layer (the inset). The high-resolution transmission electron microscopy (HRTEM) image (Fig. 1d) further confirms the successful syntheses of multi-walled carbon nanotubes (MWCNTs) at 400 8C or even down to 350 8C with H2 plasma pretreatment prior to the CVD processing. As shown in the Supporting Information (Fig. S1a),

Interfacing Neurons both Extracellularly and Intracellularly Using Carbon—Nanotube Probes with Long-Term Endurance

This study demonstrates that carbon nanotubes (CNTs) can be fabricated into probes directly, with which neural activity can be monitored and elicited not only extracellularly but also intracellularly. Two types of CNT probes have been made and examined with the escape neural circuit of crayfish, Procambarus clarkia. The CNT probes are demonstrated to have comparable performance to conventional Ag/AgCl (silver/silver cloride) electrodes. Impedance measurement and cyclic voltammetry further indicate that the CNT probes transmit electrical signals through not only capacitive coupling but also resistive conduction. The resistive conduction facilitates the recording of postsynaptic potentials and equilibrium membrane potentials intracellularly as well as the delivery of direct-current stimulation. Furthermore, delivering current stimuli for a long term is found to enhance rather than to degrade the recording capability of the CNT probes. The mechanism of this fruitful result is carefully investigated and discussed. Therefore, our findings here support the suggestion that CNTs are suitable for making biocompatible, durable neural probes of various configurations for diverse applications.

Novel glass microprobe arrays for neural recording

The probe array is a useful tool for neurophysiology to detect and record neural signals. Thus, the better understanding of neural systems can be achieved. Microfabricated probes have been widely used since fine-spacing probes with well-defined electrodes in smaller footprint can be created. This study presents a novel process to realize glass 2D-microprobe array. Dielectric material like glass can provide better signal isolation capability and biocompatibility. The through silicon vias (TSVs) can also be integrated with the glass 2D-microprobe using the micromachining process. The vertical integration of chips containing glass 2D-microprobe array is realized using these silicon TSVs. The 3D-microprobe array can be easily implemented after vertical assembly of 2D-microprobe chips using bonding. In application, the 2D glass microprobe is fabricated and characterized with a low impedance of 439 kOmega at 1 kHz. The action potential of crayfishs nerve cord has successfully been recorded using the glass microprobe with peak-to-peak amplitude of 228 muV, and SNR of 46.42. The spontaneous spike of rats cortex has also been recorded by the glass microprobe with peak-to-peak amplitude of 90 muV, and SNR of 19.72.

A pseudo 3D glass microprobe array: glass microprobe with embedded silicon for alignment and electrical interconnection during assembly

This study presents a process for the assembling of a pseudo 3D glass microprobe array. A glass microprobe with embedded silicon (ES) is batch fabricated by a glass reflow process. The silicon fixture and carrier for the assembly are also batch fabricated by silicon micromachining processes. First, the chips with a glass microprobe array are bonded by parylene-C to form the pseudo 3D glass microprobe array. The pseudo 3D microprobe array is then mounted on the silicon carrier. ES is employed for alignment during the assembly, and also acts as the electrical routing for signal recording. In application, the impedance of this glass microprobe is measured, and at 1 kHz it is 1.1 MΩ. Action potentials from rat brain cortex are also successfully recorded.

Die-level, post-CMOS processes for fabricating open-gate, field-effect biosensor arrays with on-chip circuitry

Field-effect sensors have been applied extensively to numerous biomedical applications. To develop biosensor arrays in large scale, integration with signal-processing circuits on a single chip is crucial for avoiding wiring complexity and reducing noise interference. This paper proposes and compares two CMOS-compatible processes that allow open-gate, field-effect transistors (OGFETs) to be fabricated at the die level. The polygates of transistors are removed to maximize the transconductance. The CMOS compatibility further facilitates the monolithic integration with circuitry. Based on images and electrical measurements taken at different stages of the post-CMOS processes, a more feasible and reliable process is identified. The robustness of the fabricated OGFETs against the micromachining process and against moisture is further examined and discussed. Finally, the capability of the OGFETs in detecting ion concentrations, biomolecules, and electrophysiological signals is demonstrated.

Glutamate Stimulates Local Protein Synthesis in the Axons of Rat Cortical Neurons by Activating α-Amino-3-hydroxy-5-methyl-4-isoxazolepropionic Acid (AMPA) Receptors and Metabotropic Glutamate Receptors

Background: Transient rise of extracellular glutamate occurs in the developing brain. Results: Glutamate stimulates axonal translation by binding to AMPA receptors and metabotropic glutamate receptors and activating Ca2+ and mTOR signaling. Conclusion: Exposure to glutamate rapidly up-regulates local translation in migrating axons. Significance: Glutamate-induced stimulation of local translation partakes in regulating axonal functions during development. Glutamate is the principal excitatory neurotransmitter in the mammalian CNS. By analyzing the metabolic incorporation of azidohomoalanine, a methionine analogue, in newly synthesized proteins, we find that glutamate treatments up-regulate protein translation not only in intact rat cortical neurons in culture but also in the axons emitting from cortical neurons before making synapses with target cells. The process by which glutamate stimulates local translation in axons begins with the binding of glutamate to the ionotropic AMPA receptors and metabotropic glutamate receptor 1 and members of group 2 metabotropic glutamate receptors on the plasma membrane. Subsequently, the activated mammalian target of rapamycin (mTOR) signaling pathway and the rise in Ca2+, resulting from Ca2+ influxes through calcium-permeable AMPA receptors, voltage-gated Ca2+ channels, and transient receptor potential canonical channels, in axons stimulate the local translation machinery. For comparison, the enhancement effects of brain-derived neurotrophic factor (BDNF) on the local protein synthesis in cortical axons were also studied. The results indicate that Ca2+ influxes via transient receptor potential canonical channels and activated the mTOR pathway in axons also mediate BDNF stimulation to local protein synthesis. However, glutamate- and BDNF-induced enhancements of translation in axons exhibit different kinetics. Moreover, Ca2+ and mTOR signaling appear to play roles carrying different weights, respectively, in transducing glutamate- and BDNF-induced enhancements of axonal translation. Thus, our results indicate that exposure to transient increases of glutamate and more lasting increases of BDNF would stimulate local protein synthesis in migrating axons en route to their targets in the developing brain.Glutamate is the principal excitatory neurotransmitter in the mammalian CNS. By analyzing the metabolic incorporation of azidohomoalanine, a methionine analogue, in newly synthesized proteins, we find that glutamate treatments up-regulate protein translation not only in intact rat cortical neurons in culture but also in the axons emitting from cortical neurons before making synapses with target cells. The process by which glutamate stimulates local translation in axons begins with the binding of glutamate to the ionotropic AMPA receptors and metabotropic glutamate receptor 1 and members of group 2 metabotropic glutamate receptors on the plasma membrane. Subsequently, the activated mammalian target of rapamycin (mTOR) signaling pathway and the rise in Ca(2+), resulting from Ca(2+) influxes through calcium-permeable AMPA receptors, voltage-gated Ca(2+) channels, and transient receptor potential canonical channels, in axons stimulate the local translation machinery. For comparison, the enhancement effects of brain-derived neurotrophic factor (BDNF) on the local protein synthesis in cortical axons were also studied. The results indicate that Ca(2+) influxes via transient receptor potential canonical channels and activated the mTOR pathway in axons also mediate BDNF stimulation to local protein synthesis. However, glutamate- and BDNF-induced enhancements of translation in axons exhibit different kinetics. Moreover, Ca(2+) and mTOR signaling appear to play roles carrying different weights, respectively, in transducing glutamate- and BDNF-induced enhancements of axonal translation. Thus, our results indicate that exposure to transient increases of glutamate and more lasting increases of BDNF would stimulate local protein synthesis in migrating axons en route to their targets in the developing brain.

Three-dimensional flexible microprobe for recording the neural signal

In this paper we have designed, fabricated and tested a novel three-dimensional (3D) flexible microprobe used for recording the neural signals of lateral giant (LG) on the escape system of America crayfish. We report an electrostatic actuation process to fold the planar probes to be the arbitrary orientations of 3D probes for neuroscience application. The batch assembly method based on electrostatic force techniques gave more simple fabrication compared with others. A flexible probe could reduce both the chronic inflammation response and material fracture when animal breathes or moves. Furthermore, the cortex corresponds to hypothetical cortical modules with mostly vertically organized layers of neurons. Therefore the 3D flexible probe suits to understand how the cooperative activity for different layers of neurons. Advisedly, we present a novel fabrication for 3D flexible probe by using parylene technology. The mechanical strength of the neural probe is strong enough to penetrate into a bio-gel. At the end, the flexible probe was used to record neural signals of LG cell from America crayfish.

Implementation of fully-differential capacitance sensing accelerometer using glass proof-mass with Si-vias

This study presents a novel fully-differential capacitive sensing accelerometer design consisting of glass proof-mass and Si-vias. The accelerometer with glass proof-mass has three merits, (1) the insulation glass proof-mass and conducting Si vias enable the gap-closing fully-differential electrodes design, (2) the electrical routings on insulation glass proof-mass can reduce parasitic capacitance, (3) the proof-mass is significantly increased by the nearly whole wafer thick glass material. In application, the fully-differential accelerometer with glass proof-mass is fabricated and characterized. The preliminary measurement results demonstrate the sensitivity of accelerometer is 14.44mV/G with a nonlinearity of 4.91%.