We entered the week full of hope and confidence. However, life in the lab is sometimes unpredictable. You live, learn, and move on. Having done all the background research, we had established our plan for the week. This week’s focus was all about refinement. We were destined to move forward with leaps and bounds. Geared with a new instrument, which would allow us to duplicate last year’s work within a few days. This in itself would be a remarkable feat because we could validate our previous data and finally move on testing our samples via fluorescence. However, the lab gods had other plans.
Last year’s design utilized TiO2 solutions which had nanoparticles that averaged about 70nm in diameter. One of the complications was each particle varied in size, thus producing some discrepancies. In order to mitigate the variances, this year we would have two standardized nanoparticles TiO2. One being 18nm rutile and the other 30nm anatase.
We commenced the analysis by creating the two different colloid suspensions using the two different sizes of TiO2. Both solutions had approximately 1.6mg of their respective nanoparticle and 40mL of water, which were dispensed into two separate 50mL centrifuge tubes. The two samples were then placed in a sonicator. A sonicator applies sound energy to agitate the particles throughout the solution. After sonication, the samples were allowed to rest for a day in order to evaluate their suspension. Day one was a success!!!!
Nonetheless, 24hrs later a good percentage of the TiO2 remained in suspension with a small amount of precipitate observed at the base of both test tubes. This was a delightful sign because last year a good amount of the particles did precipitate to the bottom of the tubes, which posed a major challenge when conducting further studies.
The following day came upon us. Both my mentor and I knew this day would be critical. We aspired to measure the zeta potential of both solutions at different pH’s. The zeta potential is the potential difference (measured in mV) between the dispersed particle and the surrounding fluid. The zeta potential measurement is key in determining the stability of a colloid in solution.
Meaning if the solution has an optimal zeta potential then there is an elevated resistance to aggregation (which is what we are looking for). In regards to our nanoparticle solution, which is a small colloid, then a high zeta potential (+ or -) measurement shows an excellent resistance to aggregate. On the other hand, small colloids with a low zeta potential tend to coagulate or precipitate out of solution.
We went ahead and proceeded to assess the zeta potentials of both the 18nm and 30nm TiO2 in water and at different pHs in order to determine our next plan of action.
I carried this task out manually last year, which was time consuming, tedious, and took up most of my time in the lab. This time around we were prepared with a titration instrument, which is linked to a zeta potential analyzer. This instrument would complete 3-4 days worth of work into just several hours. However, this would not be the case.
We attempted 3 trials and did not attain the results we were hoping to observe. We had many difficulties with the titration of the acid and base solutions in order to reach our target pHs. The instrument would not properly adjust the pH as we had set into the parameters.
Yet, this is what the research is all about. A problem arises, you solve the problem, then move on to the next. We spent two days troubleshooting and to no avail. We are hoping this Monday that we can get through our obstruction and continue as planned. Will keep you all posted!!!