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.

I spoke last time about how treating the glass slides with sulfuric acid resulted in optimal conditions to achieve a relatively homogeneous dye coating for fluorescence confocal microscopy. Using this new discovery, I went on and made fresh medium and thin SCNP slides to be analyzed (medium = 50 nm silica shells, thin = 10 nm silica shells). Luckily, the background fluorescence was much more uniform for these new slides as we hoped. However, the actual enhancement ratios due to the presence of SCNPs left much to be desired. According to past research, the plasmonic enhancement of a fluorophore is distance-dependent. The new electromagnetic field produced around the silver nanoparticle decays as the distance from the core of the particle increases. If a fluorophore, Rhodamine B dye, is oriented closer to the surface of the plasmonic particle then it will experience a greater electromagnetic field. Thus, in theory, 10 nm silica coating should provide the best environment for fluorescence enhancement as opposed to negligible ratios at further distances from the particle. From reading through other research papers, it seems like the typical enhancement for dye-coated thin SCNPs is approximately 10-20 times greater than dye alone. After running scans on 55 medium SCNPs and 46 thin SCNPs, it appears that our thin shells are only slightly improving fluorescence of Rhodamine B. The average enhancement for mediums was 1.16 ± 0.2 and 1.27 ± 0.27 for thins. These enhancement values are by no means statistically different, let alone anywhere near as strong as the literature standard.

In the near future we will work to figure out why our fluorescence ratios are so low, because this could pose a serious problem to the fundamental focus of our research. The issue could be as simple as the fact that we synthesized the silver colloid solutions so long ago that they are no longer displaying the desired properties (hopefully this is the case because we can always make new ones). Or the problem could lie in the methods we use to attach the Rhodamine B dye to the glass coverslips; while relatively reliable, spin-coating is perhaps not the best way to achieve a uniform dye coating.