My Research Thus Far... On this page I want to explain everything going on up to when this site was launched. Then you can just read the main page. I will try to reference this page in the news to refresh people's memories. If it gets too long, there will probably be some sort of table of contents here.
Introduction
In December 2005, I read a few different papers that described different methods of functionalizing carbon nanotubes (1-3). Scientists have found that properties of nanotubes change when they have been functionalized covalently. Pure nanotubes are small fibers that are bunched together. Functionalization frees up these bundles and changes the CNTs properties. Dr. Ellison and I settled on a combination of covalent functionalization techniques that would end in the nanotubes connected to DNA (see Figure 1 [PDF]) (1,3). The first step uses a purification technique that the other people in my lab have used in the past. It moves hot, moist air over the nanotubes, and then removes the metal catalysts using sonication in acid (4). The second step and parts of the the fourth step come directly from the literature (1 and 3 respectively). The second step is our creation. We decided on this method because Baker's reaction uses some nasty chemicals (Thionyl chloride) whereas Dyke's solvent-free reaction is simpler and uses sodium nitrite. The third step allows us to cross-link the nanotubes to DNA, in the process described by Baker, because NH2 groups are great nucleophilies. Solvent-Free Functionalization: We favored this reaction because it was simple and elegant. You can open up any Organic Chemistry textbook and read about the diazonium reaction that is utilized here (Figure 2 [PDF]). The diazonium group is susceptible to any molecule with a lot of electron density. The reaction yield seems small (20%), but that figure means that about 20% of the suface area of the nanotubes has been functionalized. The first indication (after about a mounth of trying) that the reaction worked was a color change (picture coming soon). Nanotubes are black, but our reacted nanotubes are gray. Secondly, we found that the nanotubes were soluble in DMF. Since pure nanotubes are absolutely insoluble in anything, seeing that the solubility changed is a great find. I also characterized the nanotubes using UV/Vis absorption spectroscopy (just as Dyke had done) so we could compare with the literature. We found simliar results [PDF]. As you can see, the spectrum changed from the pure nanotubes (top line) to our product (bottom line). It is hard to analyze these results; all they say is that something happened to the nanotubes, but we cannot say what. I plan to characterize the product with FT-IR during the summer so I can get a better understanding of what happened. We are happy with our results and we think that we were successful in functionalizing the nanotubes. Unfortunately, this took a whole semester to complete. I am going to continue the research this summer, and you can read about the findings on the main page. References:
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My Comments
In this little sidebar I'm going to comment on the things said on the left. See, I like to go on tangents, and separating that from the rest of the text would make this all less confusing. The inspirtation for this project came from a lecture at our school where a professor from UPenn talked about connecting DNA to quantum dots. Their research group is developing small fluorescent indicators that take advange of how quantum dot solutions change colors depending on the size of said dots. The DNA group could be used to link the quantum dots selectively to silicon to arrange the dots in a specific way. So other than the cool factor and bragging rights of being able to use carbon nanotubes and DNA in the same project, a small circuit made out of nanotubes is a direct application of the synthesis we are trying to perform. This reaction gets the award for the most misleading name ever. It is true that the reaction itself uses no solvents, which is very conveinient. However, you need to use DMF to isolate the products. For those of you that don't know, DMF (dimethylformamide) is a nastly little chemical that is toxic and probably carcinogenic (Take a look at its MSDS). It dissolves everything, including the special (read: expensive) salt plates I was using to take an infrared spectrum of my product. It also has the ability to absorb through your skin taking any chemical in solution with it into your body. Now, I would not complain if not for the fact that I went through close to a liter of it already since you need a ton of the stuff to dissolve even a little bit of our product.
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