Qiang Gui

Dry electrode for the measurement of biopotential signals

This paper introduces a kind of silicon-based dry electrode for measuring biological signals. It uses microneedle arrays to penetrate into the stratum corneum to reduce skin impedance. The dry electrode requires neither skin preparation nor the electrolytic gel, is easy to use and causes no skin allergy. Two different technologies are chosen to manufacture microneedle arrays of dry electrode. One is deep dry etching combined with isotropic wet etching. The other is mechanical dicing combined with chemical wet etching (including isotropic wet etching and anisotropic wet etching). Microneedle arrays are coated with metal and divided into 25 mm2 as dry electrode patch. Impedance testing shows that the impedance value of dry electrode can be comparable with that of commercial electrode in the 20 Hz-10 kHz frequency range. The steady-state visual evoked potential recording and analysis prove that the dry electrode can be used to detect electroencephalography.

A fiber-based implantable multi-optrode array with contiguous optical and electrical sites.

OBJECTIVE Although various kinds of optrodes are designed to deliver light and sense electrophysiological responses, few have a tightly closed optical delivering site or electrical recording site. The large space between them often blurs the stimulation location and light intensity threshold. APPROACH Based on an optical fiber, we develop an optrode structure which has a coniform tip where the light exit point and gold-based electrode site are located. The optrode is fabricated by integrating a metal membrane electrode on the outside of a tapered fiber. Half of the cone-shape tip is covered by a layer of gold membrane to form the electrode. A commercial fiber connector, mechanical transfer (MT) module, is chosen to assemble the multi-optrode array (MOA). The MT connector acts as both the holder of the optrode array and an aligning part to connect the MOA with the light source. MAIN RESULTS We fabricated a pluggable MOA weighing only 0.2 g. The scanning electron microscope images showed a tight cover of the metal layer on the optrode tip with an exposure area of 1500 µm(2). The electrochemical impedance of the optrode at 1 kHz was 100 kΩ on average and the light emission intensity reached 13 mW. The optical modulating and electrophysiological recording ability of the MOA was validated by monitoring the response of cells in a ChR2-expressing mouses cerebral cortex. Neurons that maintained high cluster quality (signal-to-noise ratio = 5:1) and coherence in response to trains of 20 Hz stimulation were monitored. SIGNIFICANCE The optrode array reduces the distance between the optical stimulating sites and electrophysiological sites dramatically and can supply multiple channels to guide different lights simultaneously. This optrode with its novel structure may lead to a different kind of optical neural control prosthetic device, opening up a new option for neural modulation in the brain.

Fabrication of Dry Electrode for Recording Bio-potentials

Development of minimally invasive dry electrodes for recording biopotentials is presented. The detailed fabrication process is outlined. A dry electrode is formed by a number of microneedles. The lengths of the microneedles are about 150?m and the diameters are about 50?m. The tips of the microneedles are sharp enough to penetrate into the skin. The silver/silver chloride is grown on microneedle arrays and demonstrates good character. The electrocardiogram shows that the dry electrode is suitable for recording biopotentials.

Implantable CMOS neuro-stimulus chip for visual prosthesis

A prototype chip with 2×2 pixels for implanting in blind patients affected by outer retinal degeneration is presented in this paper. This visual prosthesis chip imitates the degenerated photoreceptor cells, senses the incident light and stimulates the remaining healthy layers of retina or optic nerve. Each pixel integrates photodiode and stimulus pulse generator, converting the illumination on the eyes into 3-bit resolution bi-phasic current pulses. On-chip charge cancellation modules are used to discharge each electrode site for tissue safety. The prototype chip is designed and fabricated in 0.18-μm N-well CMOS (complementary metal oxide semiconductor) 1P6M Mix-signal process, with a ±2.5 V dual voltage supply. The functionality of the fabricated chip is demonstrated on anesthetized rabbits. Neural responses in visual cortex are successfully evoked by the neuro-stimulus chip through an on-board trigger interface and flexible electrode.

32-site microelectrode modified with Pt black for neural recording fabricated with thin-film silicon membrane

Multi-electrode array is an important tool in the study of neural-network, cognition, remembrance, as well as brain-computer-interface, etc. Fork-like 32-site microelectrodes are developed with silicon. By use of integrated circuit technology, the length of the electrodes, the area of the recording sites, as well as the spaces between the sites are closely controlled. SiO2/SiNx/SiO2 composite dielectric membrane and Pt black are introduced to improve the characteristics of the electrodes. The whole thickness of the thin-film probe was 21 μm. By combining the modifying process with the micro-fabrication method, this kind of silicon based microelectrode satisfies high-density recording and the performance characterization is evaluated by test in vitro and in vivo.

Low power integrated circuits for wireless neural recording applications

A group of prototype integrated circuits are presented for a wireless neural recording micro-system. An inductive link was built for transcutaneous wireless power transfer and data transmission. Power and data were transmitted by a pair of coils on a same carrier frequency. The integrated receiver circuitry was composed of a full-wave bridge rectifier, a voltage regulator, a date recovery circuit, a clock recovery circuit and a power detector. The amplifiers were designed with a limited bandwidth for neural signals acquisition. An integrated FM transmitter was used to transmit the extracted neural signals to external equipments. 16.5 mW power and 50 bps - 2.5 Kbps command data can be received over 1 MHz carrier within 10 mm. The total gain of 60 dB was obtained by the preamplifier and a main amplifier at 0.95 Hz - 13.41 KHz with 0.215 mW power dissipation. The power consumption of the 100 MHz ASK transmitter is 0.374 mW. All the integrated circuits operated under a 3.3 V power supply except the voltage regulator.

Developing a one-channel BCI system using a dry claw-like electrode

An eight-class SSVEP-based BCI system was designed and demonstrated in this study. To minimize the complexity of the traditional equipment and operation, only one work electrode was used. The work electrode was fabricated in our laboratory and designed as a claw-like structure with a diameter of 15 mm, featuring 8 small fingers of 4mm length and 2 mm diameter, and the weight was only 0.1g. The structure and elasticity can help the fingers pass through the hair and contact the scalp when placed on head. The electrode was capable to collect evoked brain activities such as steady-state visual evoked potentials (SSVEPs). This study showed that although the amplitude and SNR of SSVEPs obtained from a dry claw electrode was relatively lower than that from a wet electrode, the difference was not significant. This study further implemented an eight-class SSVEP-based BCI system using a dry claw-like electrode. Three subjects participated in the experiment. Using infinite impulse response (IIR) filtering and a simplified threshold method based on fast Fourier transform (FFT), the average accuracy of the three participants was 89.3% using 4 sec-long SSVEPs, leading to an average information transfer rate (ITR) of 26.5 bits/min. The results suggested the ability of using a dry claw-like electrode to perform practical BCI applications.An eight-class SSVEP-based BCI system was designed and demonstrated in this study. To minimize the complexity of the traditional equipment and operation, only one work electrode was used. The work electrode was fabricated in our laboratory and designed as a claw-like structure with a diameter of 15 mm, featuring 8 small fingers of 4mm length and 2 mm diameter, and the weight was only 0.1g. The structure and elasticity can help the fingers pass through the hair and contact the scalp when placed on head. The electrode was capable to collect evoked brain activities such as steady-state visual evoked potentials (SSVEPs). This study showed that although the amplitude and SNR of SSVEPs obtained from a dry claw electrode was relatively lower than that from a wet electrode, the difference was not significant. This study further implemented an eight-class SSVEP-based BCI system using a dry claw-like electrode. Three subjects participated in the experiment. Using infinite impulse response (IIR) filtering and a simplified threshold method based on fast Fourier transform (FFT), the average accuracy of the three participants was 89.3% using 4 sec-long SSVEPs, leading to an average information transfer rate (ITR) of 26.5 bits/min. The results suggested the ability of using a dry claw-like electrode to perform practical BCI applications.

A sapphire based monolithic integrated optrode

A novel kind of optrode fabricated on a sapphire substrate is proposed for optogenetic applications in neuroscience. Eight thin-film neural electrodes and a GaN-LED are monolithically integrated on the surface of a sapphire shank. The LED is used for optogenetic stimulation and the multiple electrodes are used for simultaneous recording of neural activities. The output power density of the LED is 1-19 mW/mm2 at 468 nm, driving with a current from 0.7-10 mA. The mean electrochemical impedance of the eight recoding sites on the optrode at 1 kHz is 385 kΩ. The highest temperature-raise at tissue around the LED is almost 1 °C when the output power density is 3 mw/mm2. The monolithic integrated structure will make it a powerful tool for optogenetics.A novel kind of optrode fabricated on a sapphire substrate is proposed for optogenetic applications in neuroscience. Eight thin-film neural electrodes and a GaN-LED are monolithically integrated on the surface of a sapphire shank. The LED is used for optogenetic stimulation and the multiple electrodes are used for simultaneous recording of neural activities. The output power density of the LED is 1-19 mW/mm2 at 468 nm, driving with a current from 0.7-10 mA. The mean electrochemical impedance of the eight recoding sites on the optrode at 1 kHz is 385 kΩ. The highest temperature-raise at tissue around the LED is almost 1 °C when the output power density is 3 mw/mm2. The monolithic integrated structure will make it a powerful tool for optogenetics.

Fabrication and characterization of surface-modified dry electrode for monitoring biopotential

The low and stable contact impedance between the dry electrode and skin interfaces is crucial for the acquisition of high quality biopotential signal, especially for long-term recording. Building upon this fact, poly(3,4-ethylenedioxythiophene) (PEDOT), was introduced onto the surface of dry electrode to increase the active contact area and reduce contact impedance. Silicon-based dry electrode (6 mm × 6 mm) with pyramid-like micro-needles was fabricated by a low cost method: dicing plus etching. The electrode-to-skin contact impedance (ESCI) measured on subjects proved that dry electrodes with PEDOT surface-modification have better electrical properties than that without PEDOT surface-modification. Besides, PEDOT modification combined with the microfabrication process can provide a rapid, cost-effective and high-yield method to manufacture dry electrode.

Multi-channel microelectrode array for cortical recording and stimulation: Fabrication and modification

The fabrication of silicon-substrate multi-channel microelectrode arrays for single neuron recording as well as modification of two materials to optimize the neural tissue-electrode interface were investigated. By use of multi-project wafer (MPW) model, six kinds of microelectrode arrays with different recording sites arrangement were simultaneously fabricated from one 4-inch wafer. To improve electric characteristic and biocompatibility, conducting polymer poly(3,4-ethylenedioxythiophene) (PEDOT) and multi-wall carbon nanotube (MWCNT) were used to modify the surface of microelectrode. The modified microelectrode exhibited better electrochemical characteristics, including a particularly high safe charge injection limit and low electrode impedance, as well as high signal-to-noise ratio in vivo. All of these characteristics are desirable for an implantable neural microelectrode and the modification method can be widely used to modify other neural interface devices.