Toot My Horn

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.

A Little Taste of Mushy-Brain Syndrome

I've returned from SPIE Defense Security & Sensing both refreshed and also mentally exhausted. It was a multi-day bombardment of all things awesome in the world of remote environmental sensing and other similar fields. In fact, I left a day before the conference was scheduled to end because I knew my brain would turn to mush if I stayed for the entire duration. I know this because I stayed for the whole shebang last year and, although I learned much, could make little of the notes that I had taken once I returned. Those conference sessions seemed to boil together into a steamy stew of science in my brain. I kept getting confused between different sensing mechanisms and who, of the talks that I particularly enjoyed, gave talks about which subject...'Now, I think that was the Air Force Research Lab that's doing the aptamer-based sensors...or was it MIT? Oh no...'

This year at the conference, I tried to stick with sessions that were at least somewhat related to my research, which means that I strayed away from imaging and target detection and tracking and instead mostly attended sessions on environmental and chemical sensing and the like. It didn't take long for me to notice a very obvious trend. In fact, I noticed it on the very first morning when I gave my talk. I would've been a fool to not notice it because the topic every other speaker in my session presented was on a particular type of research. That research, you may be wondering, was SERS. SERS, not to be confused with SARS, stands for surface-enhanced Raman spectroscopy. To get a picture of how SERS works, let's start with the end in mind. And when I say 'end,' I mean the last two letters of the abbreviation: RS. Raman spectroscopy is a method of analyzing Raman scattering, the inelastic scattering of incident photons, from a species. The wavelength or wavelengths at which Raman scattering occurs are related to the vibrational energy of the molecular species, so that every molecule or compound has a particular Raman spectral fingerprint. By analyzing a particular sample, the Raman spectrum can be compared to known spectral fingerprints to identify the molecular makeup of the sample. The problem, however, is that Raman scattering is very weak, and this is where the first two letters, SE, come into play. Surfance enhancement of the Raman signal can be created when the sample being interrogated is applied to a nano-structured metallic surface. The gaps between nano-scale structures are tiny little amplifiers of the Raman scattering effect, most likely caused by local surface plasmon resonance effects.

This method of analyzing and identifying particular compounds with SERS is quite effective and also thoroughly documented, and so the primary research focus was on how to enhance the effect with various surface processing techniques and use of newfangled light sources, and also on how to apply this signal transduction method to a broader sensing platform. More specifically, how to grab the analyte of interest out of the environment so that SERS can be used to interrogate it. In fact, one group from the Army Research Lab was combining SERS signal transduction with molecularly imprinted polymers as a method for capturing the analyte. The reason this is of particular interest to me is because I also work with imprinted polymers and I found the entire scheme to be quite brilliant in its simplicity and effectiveness. However, I also realize from working with imprinted polymers that in practice there is absolutely nothing simple about it.

I have to admit that there were many other topics besides SERS that were discussed during the chemical and environmental sensing sessions at this year's Defense Security & Sensing. I noticed that laser-induced breakdown spectroscopy (LIBS) was a recurring theme, as was ion mobility spectroscopy (IMS), but SERS was overwhelmingly the most popular subject within the sessions that I attended. And now that I've got the topics that I was most interested in (and I'm probably the only one interested in them) out of the way, I will return shortly with another post that shares some of the more wicked-cool things that I learned about at this year's SPIE Defense Security & Sensing conference.

Science Can Even Make Beer Taste Better

As you may know, my research emphasis is in optical sensing technologies. You may also know that my current research focuses on the use of imprinted polymers as a method of detecting the presence of a particular molecule or compound. To keep up with the trends in my field, I was conducting a brief literature search yesterday and I ran across a news article about imprinted polymers. The article, published in Science Daily, describes a research group that is utilizing an imprinted polymer to remove a compound from beer that drives photo-oxidation of beer and other beverages. My jaw hit the floor. Not only is this idea totally awesome, but I've been considering contacting brew masters in the area to discuss potential research projects that could be applied to the beer making industry. After all, my dream since the age of 10 was to become a brew master. What better way to use my expertise in biological engineering than to apply it to my childhood aspirations?

Anyways, I wanted to quickly summarize how this process works so that you can appreciate the beauty of its simplicity. Molecular imprinted polymers, or MIPs, begin as a liquid solution that contains all the necessary reagents to create a solid polymer matrix. While still in an unpolymerized fluid state, the molecule that you are interested in grabbing from the environment, called the template, is added. In this case, the template would be Riboflavin - the compound that causes beer to become photo-oxidized (also referred to as light-stricken). At this point, crosslinking of the solution is initiated by an input of energy, most often in the form of heat, and you end up with a solid polymer that contains bound Riboflavin. Now comes the important part: the Riboflavin is chemically extracted from the polymer, leaving behind binding sites that are chemically- and shape-specific to Riboflavin. When the MIP is then re-exposed to a solution that contains Riboflavin, such as beer, the Riboflavin binds to the imprinted binding sites of the MIP, the polymer is removed from the beer taking the bound Riboflavin with it, and you end up with Riboflavin-free beer. So by simply dipping this polymer into the liquid, you can create a beer that is considerably less susceptible to becoming light-stricken, keeping the beer tasting fresh and hoppy for much longer.

What a wonderful world in which we live!