Next Step: Titanium Dioxide

During my last week of research, I started a new phase of my project. After completing the study of the electron transfer dynamics of the dye Rhodamine 560 on glass, I moved on to studying the behavior of this dye on titanium dioxide. While we can learn a lot from the studies of R560 on glass especially when we compare it to other rhodamine dyes on glass, that entire phase of experimentation was just a control for comparison with the results on titanium dioxide. In actual dye-sensitized solar cells, the application of this research, titanium dioxide or some other semiconductor is necessary for the generation of electricity.

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Single Molecule Blinking Traces

At the end of my last post, I mentioned that I had taken a break from trying to measure the fluorescence lifetime of individual molecules of the organic dye Rhodamine 560, since I was unable to get a lifetime curve with a high enough signal to noise ratio at single molecule concentrations. Instead, I returned to a technique called single molecule blinking, which allows us to observe changes in emission intensity while an individual molecule is under continuous excitation.

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Bare Nanoparticle Quenching and Future Work

Towards the end of this summer I was able to reproduce fluorescence quenching on bare nanoparticles. Upon photoexcitation by the laser (or sunlight), there is a locally enhanced electromagnetic field produced around the nanoparticle. As mentioned in previous posts, a fluorophore oriented closer to the surface of a plasmonic particle will experience a greater EM field. However, fluorophores located too close or touching the surface of a particle will undergo quenching of fluorescence because of the significantly stronger EM field. To save some time, I will not go into a lengthy discussion on the exact science behind quenching, mainly because I don’t understand most of it. In this context all we are concerned with is the fact that fluorophores located on the surface of bare nanoparticles are showing a decreased fluorescence enhancement. As opposed to positive ratios, the quenched particles show up as dark spots on a bright background, meaning these particles are emitting less photons than the background dye. A typical correlated fluorescence scan and LSPR image of bare NPs can be seen below. After analyzing 25 particles, the average enhancement was 0.84 ± 0.07. 25 particles isn’t necessarily a substantial amount, but the quenching measurements thus far prove the background theory.

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Analyzing Fluorescence Enhancement for Medium-Thick SCNPs

Sorry for the long hiatus, the last few weeks of research were quite hectic. Simultaneously trying to wrap-up experimentation for the summer, compiling tons of data, and preparing for the coming semester is a daunting task.

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Correlating Single Dye Molecule Fluorescence with Nanoparticle LSPR

It’s always tough when research doesn’t go the way you initially planned. Spending weeks on a certain project only to discover that the data doesn’t fully prove the hypothesis is beyond frustrating. Alas, that’s science.

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