Thermochemical Nanolithography for use in Cancer Diagnosis
~Michael Hunter Cochran~
Supervisor: Dr. Robert Szoszkiewicz
This program is funded by the National Science Foundation through grant number PHY-1157044. Any opinions, findings, and conclusions or recommendations expressed in this material are those of the author(s) and do not necessarily reflect the views of the National Science Foundation.
Welcome, my name is Michael Cochran and I’m currently an undergraduate at Union University. This page summarizes my experience doing summer research in KSU’s Szosz-Lab.
The atomic force microscope (AFM) has given researchers many ways to understand and affect material on the nanoscale. My goal this summer was to use an AFM to thermally modify the surface of a polymer, which would later be immersed in a solution of biomarkers in the hope that those particles would attach specifically to the thermally changed areas and later be used to test for cancer.
Upon arriving at K-State, my first task was to read and understand the basics behind atomic force microscopy in “contact mode.” In essence, this can be pictured as a cantilever with a sharp tip underneath its end, a scanner upon which the sample rests, and a photodetector. (The setup can be seen here). The idea is that a laser reflects off the back of a cantilever and into a photodetector. As the cantilever is lowered into contact with the sample, its deflection is proportional to the force exerted by the tip on the surface. By choosing a set force/deflection, the scanner can move along the x and y directions while also moving the sample up and down to maintain a constant force; the scanner achieves this by receiving information from the photodetector, since a change in deflection also corresponds to a change in the light shed on the photodetector. Further, the software I used took the z adjustments made by the scanner and reconstructed the topography of the surface!
Next, I learned about thermal cantilevers and how to calibrate them, since it was necessary to control the temperature of the tip for my experiments. The thermal cantilever was used as a resistor in a circuit so that as I applied greater voltages, the power dissipated across the resistor increased and thereby also increased the temperature on the tip. Scanning with a hot tip allowed for chemical changes to the polymer surface, which would later be utilized.
With these tools, my task was to take a polymer sample and thermally modify 10 micrometer by 10 micrometer areas. Afterward, I removed the thermal cantilever, loaded a non-thermal cantilever cartridge, and then rescanned the areas I had modified. In particular, I made 2 micrometer by 2 micrometer scans within the modified areas so that after immersion I could see clearly whether or not biomarkers attached specifically. Sadly, the biomarker bath destroyed my sample. Not only was I unable to see biomarkers, but I couldn’t even find the areas I had modified. This was a great mystery at first because I was not sure that the sample was “destroyed.” This conclusion was formed after many more tests.
Thus, much of my time was spent trying to discover how the sample was being destroyed. At first I thought I was simply making an error and that I only needed to repeat the current procedure more carefully, but after three re-attempts it became clear to me that something else was amiss. Speaking with Dr. Szoszkiewicz, we came to think that the process of rinsing and drying the polymer after immersion may have been too harsh. We altered that process but the results were still negative, so I took five previously used polymer samples and re-immersed three in water and the rest in biomarker solution. This might sound strange, since the polymer on these old samples had already been destroyed, but earlier I noticed that after immersion there were always vestigial polymer islands on the surface of the sample. I simply took microscope pictures of these islands before and after re-immersion to observe the effects. To my surprise, re-immersing the polymers in water had no effect on the polymer islands, whereas re-immersion in biomarker solution caused an upheaval. This indicated that the washing procedure wasn’t nearly as destructive as the biomarker solution itself. Dr. Szoszkiewicz suggested that I dilute the biomarker solution, so I did and found that it only mildly changed the surface of the old samples. Thus, I proceeded using various dilutions of biomarker solution, which, although resulting in less damage to the polymer, still marred the surface and my thermochemical work. During one trial, the thermally modified regions and polymer were not destroyed. However, I was unable to see biomarkers attached to the modified regions.
Further work would require the development of either (1) a better process of biomarker immersion that does not destroy the polymer, or (2) a fuller understanding and adjustment of the biomarker solution. Also, there is still much to be done in the way of testing functionalized polymers with homogenized cancer tissue. Given more time, I am confident that we would have found an ideal way to immerse and preserve the polymer. The fruit of these last few weeks was particularly helpful in seeing and working around various levels of damage caused by the biomarker solution.
My family moved 10-11 times before I left for college, but I have my deepest roots in Northwest Arkansas. As to weather, I prefer rain and snow, and I think “About Me” sections are awfully hit-or-miss. I find it difficult to identify myself by a list of attributes, preferences, and experiences. However, if you would like to know something specific about me, please feel free to email email@example.com
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