Have you ever watched colloids dry?

At the beginning of the summer I developed a series of steps that I need to complete in order to have a successful summer researching auto paints. The first step was stabilizing the colloidal silver nanoparticles that my lab uses; we call them colloids for simplicity. Colloids are a suspension of silver nanoparticles in a sodium citrate and water solution. Stable colloids can be applied to auto paint samples, amongst other substances, for surface-enhanced Raman spectroscopy analysis. The trick is getting them to remain stabilized. Over the past semester, our colloids were only stable for a max of two days. The lifespan of colloids should be upwards of two weeks. After reviewing the procedure that we had been using all semester, we found some flaws. We discovered that our sodium citrate was expired by three years and that we were not boiling the silver nitrate enough before adding the sodium citrate. We corrected these two details and now we have colloids that last for three weeks! With stabilized colloids, I am able to move on to step two, reproducibility of auto paint standards.

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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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Data, Thou Art A Fickle Mistress

Since my last blog, I have run A LOT of fluorescence scans on silica coated silver nanoparticles. It’s safe to say that my daily emotions are directly linked to the outcomes and efficiency of these scans. One day I could successfully analyze fluorescence enhancement ratios for up to 20 nanoparticles and another day I could get as little as 2. For instance, I severely misaligned the laser on accident one day and it took us over an hour to fix the problem! Sometimes I feel like even the laser hates Mondays…But, alas, I am making progress on compiling data.

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