Sanyuan Chen

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 strongly adherent platinum black coatings on microelectrodes array

Platinum black coating can effectively improve the performance of MEAs (microelectrodes array) in neural signal transduction, though its lack of adhesion strength and durability tampers its usage in long term experiments. Here a new method of composite electrodeposition provides highly adhesive platinum black coating that enables MEAs for a month’s long task and repeatable utilization. The new method was compared with present techniques on multiple aspects, e.g. actual surface area, surface morphology, interfacial impedance, durability and real application tests. Results show that the new composite coating provides greatly improved durability without compromising its performances. Neural cells were cultured on these MEAs for 40 days in vitro and spontaneous action potentials with high signal/noise ratio were recorded. Theoretical model and simulation provided preliminary understanding on the mechanism of this strengthened platinum black coating.

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.

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.

Real-time multi-channel system for neural spikes acquisition and detection

A real-time multi-channel system for neural spikes acquisition and detection is presented in this paper. It incorporates self-designed micro-machined silicon recording probes, specific multi-channel biomedical amplifiers, analog-to-digital converters and a digital signal processor. The system can inspect 32 channels of neural signals, detect the spikes simultaneously, and display 1 channel of the original signals and 32 channels of detection results on the PC screen. The function of the system is verified in a saline environment and the accuracy of the spike detection is 95%. Such system can be used as a head stage for free-moving and long-term recording, and even closed-loop recording and stimulating applications.