My most recent manuscript submission has been published online. As I promised in a previous post to link to the paper on my blog, you can find the article here (probably requires a subscription). This paper doesn't include any mind-blowing discoveries, so I'm not going to spend a whole lot of time hashing out all the details of the study. But here's a brief picture of what was done...
The paper is titled, "Comparison of molecular imprinted particles prepared using precipitation polymerization in water and chloroform for fluorescent detection of nitroaromatics." First off, I've described the process of molecular imprinting and how the molecular imprinted polymers work; you can find this information here if you'd like to know more. In essence, a molecularly imprinted polymer is a plastic material that starts as a liquid-phase precursor solution containing the template molecule that you want to imprint. When the material polymerizes, creating a rigid solid, the template is physically and chemically bound within the material. A chemical extraction process is then used to remove the template molecules within the material. This leaves behind binding sites in the polymer that, when re-exposed to the template, are able to specifically rebind the molecule. In this case, I used two different template molecules, TNT (the explosive) and its little brother DNT. Both of these compounds are nitroaromatics and are important in the detection of bombs, IEDs, landmines, etc.
For this study, I prepared the imprinted polymer particles using precipitation polymerization. In precipitation polymerization, the liquid precursor of the imprinted polymer contains an excess of solvent. When there is enough solvent, one section of forming polymer in the solution is unable to link up to another forming section of polymer in the solution because of all the solvent that is between them. Because of this, discrete particles of imprinted polymer are formed within the solution.
The selection of what type of solvent to use for this process is very important, as it determines how effectively the imprinted polymer binding sites will bind to the template molecule. In previous work, I experimentally determined that chloroform was the best solvent for imprinting nitroaromatic molecules. But here's the catch: molecularly imprinted polymers bind the template molecule best when they are exposed to the molecule in the same solvent that was used to form the imprinted polymer, and I wanted to expose the imprinted polymer to the template molecule in a water environment. So there's a trade-off going on. On the one hand, I already knew that chloroform was the most effective solvent for imprinting. But on the other hand, water would be the ideal solvent if I planned to expose the imprinted polymer to the template in water.
So I set out to compare the two solvents, chloroform and water, but a funny thing happened along the way. I used scanning electron microscopy (SEM) images to look at the polymer particles and found that they were nothing alike. In the image below, (a) is the SEM of the particles produced in chloroform and (b) is of the particles produced in water. The images showed us that not only was the chemistry of the two polymers different because of the solvents, but the entire morphology was different as well.
To test which polymer would bind the TNT and DNT templates best, I doped the imprinted polymer particles with a fluorescent dye. When the template bound to the binding sites of the imprinted polymer, it would then quench the fluorescence of nearby dye molecules, which could be detected using a spectrometer. By carefully analyzing the data from these studies, I found that chloroform was the most effective solvent. This meant that the increased imprinting efficiency of the chloroform-based polymer was more important than using the same solvent for polymerization and rebinding. These results weren't much of a surprise, but they could be very beneficial for other researchers working in this field, as they can now refer to my paper rather than conducting this fairly time-consuming study on their own.
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