Development of Electrochemical Microsensors for in vivo Neurotransmitter Detection

Everything that happens in our body and all the interactions we have with the outside world are controlled by our brain. Studies of neurotransmitters are critical for a better understanding of how our brain works. Fast-scan cyclic voltammetry (FSCV) is the most popular electrochemical technique for the in vivo detection of electroactive neurotransmitters and neurochemicals with high temporal resolution. To further improve the detection selectivity, sensitivity, and spatial resolution, carbon nanomaterial based microelectrodes are applied to enhance FSCV for the neurotransmitters detection. In this thesis, I introduce and discuss synthesis and fabrication of several novel carbon nanomaterials, the effect of different surface modifications, and their applications for in vivo neurotransmitter detection.
Chapter 1 covers the recent advances in carbon nanomaterial based electrochemical sensors for direct neurotransmitter detection. First, strategies are compared to incorporate carbon nanomaterials into electrochemical sensors for neurotransmitter detection. Second, several new applications are highlighted as well as studies to address the remaining challenges for implementation. Chapters 2-5 describe new carbon nanomaterials and surface treatments for enhanced neurotransmitter detection. The direct growth of CNTs on metal wires is introduced in Chapter 2. Chapter 3 and Chapter 4 introduce three surface modification methods, laser treatment, O2 plasma etching, and anti-static gun treatment, to improve sensitivity, selectivity, and bio-fouling properties on CNT yarn microelectrodes. In Chapter 5, three different types of CNT fiber materials, CNT yarn, PEI/CNT fiber, and CA/CNT fiber, are introduced and compared for the detection of neurotransmitters. Surface physical properties and the electrochemical performance to neurotransmitters are characterized in these studies and correlated using Langmuir adsorption isotherm and diffusion profiles. Moreover, in vivo measurements are performed for dopamine at CNT-Nb microelectrodes and laser treated CNT yarn microelectrodes in Chapter 2 and Chapter 3. The effect of bio-fouling on CNT yarn is discussed in Chapter 4.
Chapter 6 and Chapter 7 introduce two novel electrode fabrication methods based on 3D printing: a 3D printed mold assisted microelectrode fabrication method and a novel 3D printed electrode design for fiber-like materials. The 3D printing technology with low-cost, high efficiency, and customizable design provides a new path to apply our studies on novel fiber-like carbon nanomaterials and surface modifications to broader applications.
Overall, this thesis explores the synthesis and fabrication of several novel carbon nanomaterials, the effect of different surface modifications, and their applications for in vivo neurotransmitters detection. Moreover, the electrode surface properties are also characterized and then correlated to their electrochemical performance. The systematic comparison of different carbon nanomaterials and different surface modifications provides a useful structure to evaluate which new nanomaterials would be good as electrochemical sensor and which electrode a neuroscientist might choose for different experiments.