Date of Award

Summer 2017

Document Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Micro and Nanoscale Systems

Second Advisor

Prabhu Arumugan

Abstract

Electrochemical methods are widely used for chronic neurochemical sensing, but thus far, the organic solution redox reactions fouled the electrodes' surface. It caused the reduction of sensitivity and the electrodes' lifetime.

Here, we present the boron-doped nanocrystalline diamond microelectrodes (BDUNCD) as the next generation electrode material for neurochemical sensor development. To aid in long-term chronic monitoring of neurochemicals, they have a wide window of electrochemical potential, extremely low background current, and excellent chemical inertness. The main research goal is to reduce the rate of electrode fouling due to the reaction by-products, and significantly extend their useful lifetime.

We systematically characterize the fouling mechanism at the BDUNCD microelectrode surface by investigating silver particles deposited on BDUNCD surface at different fouling conditions using customized microfluidic device. The fouling rates were carefully studied using two electrochemical techniques Fast Scan Cyclic Voltammetry (FSCV) and Amperometry (AM).

Furthermore, in-situ electrode cleaning methods were developed in PBS buffer solution. Under optimal conditions, the cleaning method extended the electrode sensitivity from ~6.5 hours to ~28 hours.

We developed a droplet based microfluidic platform to characterize three types of microelectrodes BDUNCD, nafion modified BDUNCD, and nafion multi wall carbon nanotube modified. BDUNCD dopamine signals enhance two to three times by Electrophoretic deposition (EPD) of nafion layer (50 nM), and enhance about 10 times in complementary nafion multi wall carbon nanotube modified BDUNCD. Specifically, the sensitivity, response time, and clearance rate of dopamine were determined in 9 hours of monitoring. In the presence of ascorbic acid and serotonin was studied using differential pulse voltammetry method, the selectivity comparison performs the multi-wall carbon nanotube superiority and achieved long-lasting 9 hours monitoring after nafion layer coating, it has the initial sensitivity of oxidation current DA (0.58 nA) and 5-HT (1.03 nA) with a sensitivity value of DA 1.18 µA µM-1 cm-2 and 5-HT 2.09 µA µM-1cm -2. The other advantage of multi-wall carbon nanotube modified BDUNCD electrode reduces the limit of detection to 5.4 nM (DA) and with nitric acid treatment 1.78 nM (DA).

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