Week 6 & 7 - DNA Wrapping & Starting Over

During the beginning of week 6 and 7, I continued DNA wrapping. I tried using different concentrations of each the DNA and AuNPs, however, nothing worked well. I could not replicate my very first try, which, although was not useable due to excessive aggregation, still was indicative of wrapping due to the surface charge flip from positive to negative. After trying to wrap with this sample multiple times, I concluded that these particles were simply not useable for wrapping even though the measurements were not bad. To confirm my suspicions, I still had a little bit of the pellet I used for my first attempt at wrapping, so I tried it again with that. As expected, the surface charge flipped, indicative of some wrapping. So I threw my new samples out.

Attempting to start again with wrapping, I noticed I had old citrate particles that were very good lying around. I didn't want to waste good particles, so I tried with these. It ended up being a waste of time. I coated a bunch of them with polymer, which worked out very well, and cleaned them and pelleted them. These looked much better than the other samples that I had been using.

These are old particles from the beginning of research that looked very promising under the UV-Vis. As you can see, every step is not aggregated at all and is only widening a little bit. I was hopeful that these might work.

After calculating the concentration using the method I used before, I diluted the pellet 10x in order to keep them from being too concentrated. The pellet ended up being at least 2x more concentrated than the previous pellets, so I didn't have to waste as much in order to make the same amount of solution.

After wrapping, zeta potential showed that the surface charge was still positive. However, it was only slightly positive at around 12mV. This is indicative of slight wrapping, but the majority of particles were still not being wrapped. I concluded that this was most likely due to the sample not being cleaned enough, and there was simply too much PAH floating around that the DNA could stick to instead of the particles. So I tried to clean my samples again to see if that would help. Unfortunately, this completely destroyed them in the process. The data was extremely weird, the sample looked extremely polydisperse and they had probably the most horrible looking absorption spectrum I've ever seen. However, the surface charge was 0mV. From this, I decided no more. I was going to figure out how to clean the particles and remove excess polymer without aggregating them. So I looked through a bunch of different papers.

Moving on to week 7, I had looked through a lot of different papers that coated AuNPs with all different kinds of polymers. A lot of the papers said that they centrifuged the particles at high speeds of 9000-12000rpm for a short amount of time (5 - 15min). I was surprised at this but decided to give it a try. I ended up going with the same speed and time that the people in the chem department used in order to coat with polymer, 9000 rpm for 15 minutes.

I also noticed something in the papers. Almost all of them had some form of saying, "in order to keep samples as good as possible, we always used freshly made particles for our experiments". I realized that maybe freshly made particles are just better to use than old ones, for some odd reason. It's probably because it's super hard to make perfectly stable particles, so they're always going to worsen a little bit over time. So I made new particles, batch 4, and went through all the steps. They looked very promising every step of the way.

Next week I'll start making DNA-AuNPs using my new particles.