Dec 15, 2010
Hydrophilic modification upgrades neural microelectrode
To decrease the impedance of microelectrode arrays designed for neuroscience applications, researchers in Taiwan have fabricated units based on multi-walled carbon nanotubes (MWCNT) and then modified the MWCNT surface with a steam-plasma (SP) treatment. As the physical size of a microelectrode decreases, its impedance increases and charge-transfer capability decreases. To decrease the impedance, the effective surface area of the electrode must generally be increased. In this work, the group has explored the effect of plasma treatment on the surface wettability of MWCNT.
With an SP treatment the surface of MWCNT is converted from super-hydrophobic (152°) to super-hydrophilic (~5°); this hydrophilic property is attributed to –OH bonding on the surface of MWCNT. Applying plasma with a power of less than 257nbsp;W for 10 s improved the electrochemical and biological properties, and circumvented the limitation of the surface reverting to a hydrophobic condition; a hydrophilic state is maintained for at least one month.
As shown in the figure, the morphologies of treated MWCNT (25 W, 10 sec) were not different from those as grown. For a typical electrode with an open area of 2500 µm2 immersed in phosphate-buffered saline, the impedance decreased from 51.2 kΩ to 3.49 kΩ at 1 kHz (nerve operating frequency) after SP treatment. The impedance of the treated MWCNTs is much smaller than that of electrodes made from other materials such as Au, Pt and Ir.
The modified microelectrode array was used to record neural signals of a lateral giant cell from an American crayfish. The response amplitude of the action potential was about 275 µV with a 1 ms period; the recorded data had a signal to noise ratio of up to 40.12 dB. The improved performance of the electrode makes it possible to separate the neural signals and recognize their distinct shapes.
With further development, the rapid surface treatment will be useful for long-term recording applications.
The researchers presented their work in the journal Nanotechnology.
About the author
Chang-Hsiao Chen is a PhD candidate at the Institute of NanoEngineering and MicroSystems (NEMS), National Tsing Hua University (NTHU), Taiwan. His research includes microprobe fabrication, carbon nanotube treatment, and signal processing technology. Da-Jeng Yao is an associate professor at the institute, and is also an adjunct professor in the Department of Power Mechanical Engineering and the Department of Engineering System and Science. He received his PhD from the department of Mechanical and Aerospace Engineering at the University of California at Los Angeles (UCLA), US, in 2001. His research scope combines his strong backgrounds in MEMS and thermal fluidics. Areas under investigation include BioMEMS, electronic nose devices, MEMS packaging, thermo-fluidic MEMS, and thin-film property measurement.