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Conducting Polypyrrole-based Composites: Preparation And Application For Neural Microelectrode Modification

Posted on:2012-02-11Degree:DoctorType:Dissertation
Country:ChinaCandidate:M DengFull Text:PDF
GTID:1111330338469546Subject:Materials Physics and Chemistry
Abstract/Summary:PDF Full Text Request
The implantable neural probes, composed of microelectrode arrays for neural stimulation and recording, are generated with the development of clinical medicine, materials science and micro-electro mechanical systems techniques in the last two decades, and find their applications in the treatment of many brain diseases. However, due to the high impedance of electrode-cellular interface and thus decreased signal intensity, the long-term efficiency of neural probes remains a challenge. To improve the performance of neural probes for chronic use, we need to construct a conducting polymer layer with low impedance, high charge capacity density and good biocompatibility on the neural microelectrode. This thesis focuses on developing a simple and effective method to modify the neural microelectrode with polypyrrole (PPy) and PPy-based composites, investigating the effect of synthesis parameters on the properties of modified microelectrodes as well as innovating a new composite for neural microelectrode modification.In chapter 1, the progress of conducting PPy and its composites was summarized, and the application of PPy in sensors was discussed.In chapter 2, a series of conducting PPy coatings were deposited onto neural microelectrodes under various electrochemical deposition conditions, exhibiting cauliflower-like, stacked hollow spheres, disk-like and toothpaste-like morphologies. The influence of dopant, pyrrole monomer concentration and deposition charge density on the electrochemical properties of modified microelectrodes was discussed. The electrochemical impedance spectroscopy (EIS) and cyclic voltammetry (CV) results show that, compared to the bare platinum neural microelectrode, the impedance of PPy modified microelectrode at 1 kHz decreases for 3 orders of magnitude and the charge capacity density is enlarged for 250 times. Furthermore, the biocompatibility of PPy coatings was evaluated by hippocampus cell culture.A variety of polypyrrole/graphene oxide composites (PPy/GO) were synthesized on the surface of ITO glass with electrochemical co-polymerization in chapter 3. The structure and morphology of the obtained composites were characterized via Fourier transform infrared spectroscopy (FT-IR), Raman spectra, X-ray diffraction (XRD), thermogravimetric analysis (TGA) and field-emission scanning electron microscopy (FESEM). The influence of electrochemical methods, dopant concentration, and deposition charge density on the composites' morphology was discussed. The formation mechanism of PPy/GO composites was proposed based on the experimental results. The glucose oxidase (GOD) encapsulated PPy/GO was deposited onto glass carbon electrode (GCE) to prepare a PPy/GO-GOD electrode, and its current response to glucose was evaluated.In chapter 4, by exploiting the electrostatic interaction between positively charged pyrrole cation radicals and negatively charged GO sheets, PPy/GO was deposited onto neural microelectrode with the one-step electrochemical methods described in chapter 3. PPy/GO coatings on microelectrodes demonstrated rough morphology with GO sandwiched PPy bulges on the surface. The effect of synthesis parameters, i.e., deposition charge density, dopant concentration and GO content, on the composites'morphology and electrochemical properties of modified microelectrode were discussed. The impedance of the PPy/GO coated microelectrode is only about 10% of the bare Pt electrode at 1 kHz, while the charge capacity density is more than two orders of the magnitude of the unmodified electrode. Moreover, the PPy/GO coated neural microelectrodes show higher performance than the PPy coated electrodes for the application of neural probe.
Keywords/Search Tags:Electrochemical polymerization, Polypyrrole, Graphene oxide, Neural microelectrode, Cyclic voltammetry, Electrochemical impedance spectroscopy, Conducting polymer composites
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