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In order to better understand the ionic transport properties of carbon nanotubes, we have been examining the flow rates of different ions through the nanotubes. This will be done by utilizing the hydrophobic interior, semiconductive properties, and small size of the carbon nanotubes in order to look for fluctuations in current through the nanotube. In this experiment the nanotubes used will have a carboxylic acid group attached to the ends of the nanotubes, which allows us to attract positive ions and repel negative ions due to the partial negative charge. Since the goal of the experiment is to measure changes in current through the nanotube, we need a baseline to look at first. This baseline will be provided by a flow of protons through the nanotube that will be interrupted by the analytes and cause a shift in current. Since the experiment requires a steady flow of protons through the nanotube, all of our solutions need to be relatively acidic with a pH that’s usually below 3. Since we have already successfully tested and found pore- blocking events with salt solutions such as lithium chloride, sodium chloride, and potassium chloride, our research now mainly focuses on testing pore blocking events with amino acids solutions such as glycine, dopamine, B-alanine, L-glutamic acid, and valine. The potential biological applications of ionic transport in nanotubes is the main reason for this focus, though further testing still has to be done on other biological molecules. Successful pore blocking tests have also been done with neutral molecules such as methanol, though further testing must be done to verify other neutral molecules. After the data was collected it was analyzed in order to find trends between the current, voltage, dwell time, and event amplitude. So far it’s been observed that the average event amplitude increases with voltage, though no such trend has been found so far for the dwell time and the voltage. The current and voltage can already be related through the use of Ohm’s Law. Past work done by the Strano research group at MIT will also be considered about the diameter dependence of the carbon nanotube on the rates of pore blocking. In the future we hope to try out a wider variety of amino acids and neutral molecules as well as possibly change the functional group on the ends of the nanotubes to something positively charged allowing us to test a wider variety of molecules.
Menges, Samuel G., "Ionic Transport Properties of Carbon Nanotubes" (2015). Chemistry Summer Fellows. 6.