Too much sodium!

Yesterday, I ran another equilibrium dialysis with the same parameters but I doubled the number of spins to 20.

Today, I characterized the resultant nanoparticles, prepared new calibration samples, and ran all of the dialysis samples in the ICP. I diluted the nanoparticle sample to attempt to lower the concentration range the machine was reading. There were a few interesting results. Firstly, both this sample and the last sample are reading positive charges. The polymer coat is negatively charged so the only possible explanation is that the excess sodium (3:1 Na:S in the first sample and 6:1 Na:S in the second) is causing the surface to become positive. The very presence of an excess of sodium is counterintuitive, one would assume that the polymer would only absorb enough sodium to neutralize its charge. Going forward I will be doing more ICP and dialysis to get more data. 

The Files are Breeding Like Tribbles!

On Thursday, I ran ICP on the uncoated nanoparticles and the coated pre-dialysis nanoparticles. Since  then, I have spent most of time trying to analyze the ICP data and reading literature on polyelectrolyte deposition. As a result, I have 7 excel documents open on my computer and even more pdfs!

Next week, I plan to run dialysis on the same nanoparticle sample with KCl as the salt buffer. I will then run ICP on those samples so that I can compare them to the nanoparticles that underwent dialysis with NaCl.

June 10th – Compiling Data

These past few days I have been working on compiling the ICP-AES data from multiple runs. Below is one set of the graphs that compares the results from each run. Because I am investigating the competitive binding between hexamminecobalt(III) (which has a charge of +3) and magnesium (which has a charge of +2) to DNA at varying levels of osmotic stress, the graphs below demonstrate how much of the DNA charge is neutralized by each respective species at differing PEG values. It is interesting to note all runs seem to have the same trend, and hopefully with even more data the numerical values for the trend will become more solidified. Tomorrow, I plan to run another set of samples through the ICP-AES and compare its results as well.

Dialysis

Yesterday, I finished making and characterizing a large batch of PSS coated NPs. I then tried to run equilibrium dialysis. I modified my parameters, decreasing both time and rotation speed, to hopefully correct the loss of concentration. I successfully recovered about 1.7 nM which is a big improvement over last week.

Today, I characterized the new nanoparticle sample, prepared new calibration standards, and ran ICP on the equilibrium dialysis samples.

Tomorrow, I plan to do analysis on the ICP data I have acquired and possibly run ICP on the non-dialysized PSS nanoparticles for comparison.

Sulfur!

On Friday, I ran equilibrium dialysis on my PSS coated nanoparticles using a centrifugation system. Unfortunately, a significant amount of the nanoparticles stuck to the mesh in the filter causing a significant reduction in concentration. This was a problem since we needed a relatively high concentration in order for the ICP to be able to detect sulfur, an element found in the PSS coat.

Today, we came up with two solutions. First, we purchased a different type of dialysis device that floats in water and allows equilibrium to be reached over time.

The new dialysis device will take over a week to arrive so, in the meantime, I concentrated the nanoparticle solution from Friday’s dialysis and ran it in the ICP. In the concentrating process, we lost a good deal of volume so we had to use a couple tricks to get the machine to use up less sample. From my calculations, we were not very optimistic that the machine would be able to detect the sulfur. However, much too our surprise, the sample had more sulfur than even our highest estimate. Tomorrow we will look at the official ICP report and it should be able to tell us something about the effectiveness of the dialysis and the ion atmosphere around the nanoparticles. Also, I will try to work out some better parameters for our existing dialysis system.

Polystyrene Sulfonate

Today, we ran our calibration samples in the ICP-AES to get an idea of how precisely we made our samples and to learn how to use the machine. After we finished running the samples and analyzing the results, I visited Professor Thompson’s lab in the Chemistry department where he outlined the process we will follow for the next couple weeks. Today, I diluted a solution of spherical gold nanoparticles he prepared, and treated them with polystyrene sulfonate and sodium chloride. This mixture needs to sit over night so the polystyrene sulfonate has time to absorb onto the nanoparticles surface. Tomorrow, I will centrifuge down the treated nanoparticles and begin characterizing both the treated and untreated samples.

June 3rd – Summer Research Begins!

Looking forward to an interesting and exciting summer! These past few days I have been organizing and gathering background information by reading scientific papers so I can begin research soon. Today we ran standard samples through the ICP-AES to learn how the machine works as well as determine the precision of our standards. Hopefully later this week I will be able to run some samples through the ICP-AES and begin to look at ion binding competition in DNA-arrays!

The epic quest begins…

Today was the first day of summer research! Ambitious plans were laid, literature was read, and calculations were made. My project will focus on the interactions between gold nanoparticles and DNA. My goal for the next couple weeks will be to synthesize polyelectrolyte coated gold nanospheres and characterize their features. Then I will run equilibrium dialysis and atomic emission spectroscopy (ICP-AES) on these nanospheres with different concentrations of ions. I’m looking forward to an exciting summer!

Squiggles!

I averaged all of the ICP runs from the past two weeks and compiled them onto one Excel spreadsheet. I then began looking at the Na/Co ion competition more thoroughly using the article Prof. Andresen and John Giannini collaborated on a few summers ago, “Ion Competition in Condensed DNA Arrays in the Attractive Regime” as a guide. I tried to use the ion binding model used in the article to analyze the relationship between the number of ions near the DNA arrays and the solution’s ion concentrations. This involved finding a constant, ξ, to relate the two sets of numbers (aka. the squiggle). After rearranging the formula given for a simplified ion binding model, I found a ξ for each data point. I took a rough average and an actual average and compared the values found using the ξ against the data from the ICP (shown below).

As you can see, the model only fits the middle three points. This could be due to my own error in calculating each point, the assumptions I made when using the model, the interactions due to Cl- that I neglected, or the model might not accurately represent this data.