This past semester, the IUJUR sat down with John Hoy, a sophomore working in Dr. Bogdan Dragnea's physical chemistry lab at IU Bloomington. Currently majoring in molecular life sciences and math, John's eventual goal is to work within the field of physical chemistry as a research scientist. He found out about the lab during his freshman year, when a TA for his general chemistry course was looking for undergraduates to assist with the lab. The process was informal, Bogdan showed him around and discussed their research interests, which aligned.
The lab involves encapsulating gold and gold-silver alloy nanoparticles into capsid shells from a plant virus and decorating it with dye molecules for future use in medical imaging. Using the Brome Mosaic Virus, a virus that mainly infects tobacco plants and the like, "we intentionally infect the plants and then harvest it back out," John stated. With the purified harvested virus, the lab breaks it down by extracting the genetic material. The proteins of the virus can be "disassociated from each other." Then, they have been "focusing on" reforming the capsid shell around a metal particle. Capsid shells are proteins that surround the DNA of a virus. They can be decorated with the dye molecules, showing up under fluorescent lighting. Next steps for the current stage of the lab is to perfect the metal core particle, ironing out how to add the dye to the virus shell, and using a few different dye molecules with different properties to determine the best one. John notes that the molecules have shown some really "interesting and novel optical properties," that they believe could be used in medical applications.
John's job within this project has been fine tuning the process of encapsulating the virus shell around the alloy and the "size and composition of that metal core particle." Depending on how the chemicals are mixed, it causes it to be different sizes. With the process of mixing, John states "the resolution he can tune it to" is a nanometer. The goal is for the metal core to be within 5 nanometers to 40 nanometers, roughly 1/5000th the diameter of a hair "for a sense of scale." Within that small range, John is figuring out which best lights up under the electron microscope. This process consists of taking the core particles, which start as "pure gold," dissolve them into water, and then mix in reducing agents. "We reduce the free floating gold ions charge to zero, which makes what is called a nucleation site." Other gold ions bind to the nucleation site, forming the alloy, "kind of like how a snowflake grows," John describes. Now, John is working on adding silver into the alloy, aiming to go from a 100% gold to 60% gold/40% silver alloy. It shifts the optical properties of the particle's "plasmonic resonance," changing the wavelength of light that the particles absorb. Turning to a 60% gold alloy should blend the peaks for both capsid and dye molecules, making light emit the most efficiently.
After this, the lab then checks to ensure the samples are nice by means of negative stain imaging. They do this by placing the alloy, encapsulated by the capsid shell decorated with the dye molecule, into imaging by an electron microscope. "A piece of technology from 1994, it cost over $300,000 at the time of purchase," so John mentions the need to be careful and have supervision while people use it. Dr. Barry Stein trains and supervises the use of the electron microscope, guiding the users in the lab. It contains tungsten filament that runs 8000V of electricity, allowing it to get extremely hot. It blasts electrons through a tube as magnetic lenses "reshape and direct" the electrons so they shoot through the alloy sample. The sample gets deposited onto a copper grid coated with carbon film. Blasting electrons through the sample, the electrons that don't get blocked hit a fluorescent material at the bottom, which then creates the image. This is because the electrons can pass through the virus, but cannot pass through the allow. Only the shell appears in the imaging, whereas the alloy shows up black as seen below. John mentioned this being his "favorite part of the lab", as he gets to see all of the objects he created.
