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Title:Nanopipet electrodes for the detection of neurotransmitters using the interface between two immiscible electrolyte solutions
Author(s):Colombo, Michelle
Advisor(s):Sweedler, Jonathan V.
Contributor(s):Shen, Mei
Department / Program:Chemistry
Degree Granting Institution:University of Illinois at Urbana-Champaign
Abstract:The ability to chemically characterize small domains in living systems is an important yet unmet goal. Specifically, there is still much to learn regarding the vital process of cell-to-cell communication, or neurotransmission. A nanoscale interface between two immiscible electrolyte solutions (ITIES) provides a unique analytical platform for the detection of ionic species of biological interest such as neurotransmitters and neuromodulators, especially those that are otherwise difficult to detect directly on a carbon electrode without electrode modification. In this thesis, the detection of acetylcholine, serotonin, and tryptamine is reported using nanopipet electrode probes with radii on the order of tens of nanometers. The transfer of these analytes across a 1,2-dichloroethane/water interface was studied by cyclic voltammetry and amperometry. Well-defined sigmoidal voltammograms were observed on the nanopipet electrodes within the potential window of artificial seawater for acetylcholine and tryptamine. The half-wave transfer potential of acetylcholine, tryptamine, and serotonin were examined and found to be distinct from one another, allowing for qualitative detection. The detection of these analytes was linear in the mM concentration range, and the limits of detection for acetylcholine and serotonin were found to be below the expected concentrations within a synaptic cleft. Next, the detection of dopamine (DA) at nanopipet electrodes with radii of hundreds of nanometers is presented. Dibenzo-18-crown-6 was employed as an ionophore to facilitate DA transfer, allowing for DA to be detected in a solution of MgCl2, where well-defined steady-state sigmoidal cyclic voltammograms were observed for the transfer of DA. The detection is linear for concentrations of DA ranging from 0.25 mM to 2 mM. The diffusion coefficient at these nanopipet electrodes was calculated both with and without the presence of the common interferent ascorbic acid. DA detection still shows linear behavior with well-defined sigmoidal CVs even when up to 20 mM ascorbic acid is present in solution, though the observed diffusion coefficient of DA decreases with increasing ascorbic acid concentrations. However, the physiological concentration of 0.1 mM AA had no effect on DA’s diffusion coefficient. Finally, cultured neurons from Aplysia californica were interrogated using these ITIES-based nanopipet electrodes in combination with scanning electrochemical microscopy. No external mediator was required for this process, as the assisted transfer of ASW produced successful negative feedback. This technique allowed for highly spatially resolved topographical images of neuronal processes using constant height imaging. Furthermore, cells were stimulated with a solution of high potassium and the intracellular response was recorded at the nanopipet electrodes. While significant future work is still necessary, these preliminary results show potential for these electrodes to examine the dynamics of neurotransmission in real-time.
Issue Date:2016-04-19
Rights Information:Copyright 2016 Michelle Colombo
Date Available in IDEALS:2016-07-07
Date Deposited:2016-05

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