Patent Application
20110144471
The present invention relates to a flexible probe structure, particularly to a flexible probe structure using a carbon nanotube as the electrode interface. The present invention also relates to a method for fabricating the same flexible probe structure.
In neural physiology, a neural probe is usually used to stimulate and measure neural cells to study the physiological operation statuses of nerves. When neural cells convert or transmit electric signals via the differences of the electric potentials thereof, the electrode of a neural probe can measure the intracellular or extracellular neural signals and then receive and transmit the nerve impulses created by the electric potential differences. The study of neural physiology can improve the understanding of neural diseases, such as the Alzheimer's disease, Parkinson disease, dystonia, and chronic pain.
In detecting extracellular neural signals, the neural electrode has to closely contact neural cells and electrically stimulates/detects the neural cells in a capacitive coupling way. The efficiency of the abovementioned capacitive coupling correlates with the selectivity, sensitivity, charge transfer characteristics, long-term chemical stability, and interfacial impedance between the neural electrode and the cell tissue.
The silicon-based neural probe can be fabricated with the MEMS (Micro-Electro-Mechanical System) technology and thus can massively replace the traditional metallic probe. However, the silicon-based probe is very hard and unlikely to bend or deform. When the testee moves, the silicon-based probe is likely to harm the tissue and cause inflammation, or even the original test point is displaced and the probe is detached. Therefore, the silicon-based probe is hard to satisfy the requirement of long-term implantation or real-time measurement. In Journal of Micromechanics and Microengineering, vol. 14, pp. 104-107, 2004, the research team of Takeuchi proposed a “3D Flexible Multichannel Neural Probe Array” to overcome the problem that the silicon-based probe harms biological tissues.
CNT (carbon nanotube), which was found by S. Iijima in 1991, has a superior electrical conductivity because of its special structure. Thus, CNT has been widely used in the nanometric electronic elements. CNT has very large surface area (about 700˜1000 m2/g), high electrical conductivity, better physicochemical property, better chemical inertness and better biocompatibility. Therefore, more and more applications use CNT as the neural electrode interface, for example, “Carbon Nanotubes for Neural Interfaces” by David Ricci; “Carbon Nanotube Coating Improves Neuronal Recording” by Edward et al., Nature Nanotech., 2008; “Neural Stimulation with a Carbon Nanotube Microelectrode Array” by Ke Wang et al., Nano Lett., 2006; “Carbon Nanotube Substrate Boost Neuronal Signaling” by Viviana Lovat et al., Nano Lett., 2005; and “Carbon Nanotube Micro-Electrodes for Neuronal Interfacing” by E. Ben-Jacob et al., J. Mater. Chem., 2008.
However, using the CNT as the measurement interface still has room to improve in interface hydrophilicity modification and interface impedance of the biological tissue fluid. Thus, the neural electrode of the present invention integrates a flexible substrate and an electrode interface of the CNT to perform the modification of the surface functionalization to attain higher measurement quality of the neural signals.
One objective of the present invention is to provide a flexible probe structure, which can be implanted to a creature to undertake a long-term measurement without causing inflammation of the biological tissue.
Another objective of the present invention is to provide a flexible probe structure, which is exempt from signal attenuation and signal distortion caused by high interface impedance and can obtain higher signal quality.
To achieve the abovementioned objectives, the present invention proposes a flexible probe structure, which is made of a flexible polymeric material with high-biocompatibility and has a CNT (carbon nanotube) electrode interface modified to greatly reduce the interface impedance in measurement. The flexible probe structure of the present invention comprises a base and at least one probe connected to the base. The probe has at least one electrode. The electrode is electrically connected to a metal pad on the base via a wire. The wire is insulated from the environment. The base and the probe are both made of a flexible polymeric material. The electrode has a CNT layer functioning as the electrode interface, and the CNT layer is processed with an UV (ultraviolet ray)-ozone treatment.
The present invention also proposes a method for fabricating a flexible probe structure, which comprises the steps of: preparing a flexible substrate; forming a conductive layer on the flexible substrate and defining an electrode, a wire and a metal pad on the conductive layer; forming a CNT layer on the electrode; forming an insulating layer on the conductive layer to insulate the wire from the environment; and processing the CNT layer with an UV (ultraviolet ray)-ozone treatment.
After being processed with an UV-ozone treatment, the surface of CNT has a great number of carbon-oxygen functional groups. The carbon-oxygen functional groups can greatly reduce the impedance of the interface between the electrode and the biological tissue fluid, whereby is achieved higher measurement quality and increased the adherence of the neural cells to CNT.
Below, the technical contents and embodiments of the present invention will be described in detail in cooperation with the drawings.
The embodiments of the present invention will be described in cooperation with the following drawings:
Refer to
In the flexible probe structure 10, the base 11 and the probe 12 are made of a flexible polymeric material, which is not limited to but may be a material selected from the group consisting of polyimide (PI), poly-para-xylylene (parylene), a thick photoresist SU-8, polydimethylsiloxane (PDMS) and benzocyclobutene (BCB). Thus, the flexible probe structure 10 is bendable and has better biocompatibility and a low-SNR electrophysiological signal. Further, the testee using the flexible probe structure 10 is exempt from the immunological rejection caused by silicon/metal material and thus is free from the inflammation induced by rejection. Therefore, the flexible probe structure 10 can be implanted into a creature to perform long-term measurement. Furthermore, the flexible polymeric material has a lower price and favors mass production.
In the present invention, the electrode 13 has a CNT (carbon nanotube) layer functioning as the measurement interface. The CNT layer is processed with an UV-ozone treatment. In the UV-ozone treatment, the double carbon bonds (C═C) on the outmost layer of CNT are broken by ultraviolet ray, and the carbon atoms thereof react with ozone to form a great number of carbon-oxygen functional groups, such as C—O, C═O, and O—C═O. The carbon-oxygen functional groups form dangling bonds on the surface of CNT and assist in fixing water molecules with the intermolecular bonding therebetween. The carbon-oxygen functional groups provide low-energy absorption sites for water molecules to enhance the reaction capability and charge transferring capability of the electrode 13 and the electrolyte interface mimicking the environment of the biological tissue. Further, the carbon-oxygen functional groups can greatly improve the impedance of the interface of the electrode 13 and increase the adherence of neural cells to CNT, whereby the electrode 13 can attain high-quality and undistorted neural signals. The UV-ozone treatment can improve the wettability of the CNT surface and transform the super-hydrophobic CNT surface into a hydrophilic CNT surface, whereby the CNT can apply to undertake measurement in a biological tissue full of tissue fluid.
Refer to
The present invention also proposes a method for fabricating a flexible probe structure 10. Refer to
The abovementioned steps will be described in detail below.
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In one embodiment, a CVD method is used to synthesize the CNT layer 400 on the electrode 13. Before deposition, a catalytic layer 500 having a thickness of several nanometers to tens of nanometers is formed on the electrode 13 to assist the formation of CNT. The catalytic layer 500 may be made of iron (Fe), cobalt (Co), nickel (Ni), or an alloy thereof. In one embodiment, the catalytic layer 500 is made of nickel (Ni) and has a thickness of about 5 nm; a titanium (Ti) film functioned as a second adhesion layer 600 is adhered to the conductive layer 200, and the catalytic layer 500 is then formed on the second adhesion layer 600. In one embodiment, CNT is synthesized at a temperature of 350-450° C. with a gas flow containing a carbon-source gas (such as methane (CH4), acetylene (C2H2), or ethylene (C2H4)), and an inert gas or hydrogen. It should be noted that the abovementioned embodiments are only to exemplify but not to limit the scope of the present invention.
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When the CNT layer 400 is synthesized with a CVD method, the synthesis is undertaken at a temperature higher than the melting point of the insulating layer 700. In such a case, the CNT layer 400 is formed on the electrode 13 in advance before the formation of the insulating layer 700. In another case, the sequence of forming the CNT layer 400 and the insulating layer 700 may be reversed according to different characteristics and conditions of procedures. For example, the insulating layer 700 can be formed first, and then the CNT layer 400 is formed in a manner that does not damage the insulating layer 700 and the flexible substrate 100 on the electrode 13.
Next, the CNT layer 400 is processed with an UV-ozone treatment. In the UV-ozone treatment, CNT is illuminated with ultraviolet ray in an atmosphere of ozone, whereby the surface of CNT reacts with ozone to form carbon-oxygen functional groups, such as C—O, C═O, and O—C═O. In one embodiment, the ultraviolet ray has an illumination intensity of 25-35 mW/cm2 and a wavelength of 254 nm. Refer to
Because of adopting a flexible substrate, the flexible probe structure 10 of the present invention is easy to fabricate and has a lower cost. Further, the surface modification of CNT promotes the measurement performance of the flexible probe structure 10 of the present invention.
The embodiments described above are only to exemplify the present invention but not to limit the scope of the present invention. Any equivalent modification or variation according to the spirit and technical contents disclosed in the specification and drawings is to be also included within the scope of the present invention.
