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.

Despite the setbacks this summer, it seems like the obstacles I faced may have only been slight detours. Towards the end of spring semester, two students in my lab worked to synthesize medium-thick silica-coated silver nanoparticles in order to fill the gap between the 8.6 and 51nm shells. This was done in the hopes of compiling a more rounded enhancement database. By the conclusion of our study on the distance dependence of plasmonic enhancement, we would like to have data for a sufficient amount of shell thicknesses to determine exactly where enhancement is the greatest and where it begins to taper off. Specifically, they grew 25nm and 35nm shells. However, due to problems with the school’s TEM machine they were not able to affirm the exact thicknesses. Transmission Electron Microscopy is a technique where an electron beam is transmitted through a thin sample (nanoparticles) and interacts with the sample as it passes through. An image is then formed from the interaction with the electrons, which can be further magnified and focused. TEMs have the capability of imagine much higher resolution than other microscopes and thus can examine fine details such as the exact size of nanoparticles or nanometer-thin silica shells. Below is a typical example of what TEM imaging looks like, where (a) is an 8.6 nm silica shell on a silver nanoparticle, (b) is 9.1 nm, (c) is 51 nm, and (d) is 75 nm.

TEM various shell thickness

Thus, while any fluorescence data taken from these samples is insignificant until we figure out the exact measurements, these samples represent the freshest colloid solutions to compare to the old ones. And, not surprisingly, they have showed equal to greater enhancement ratios than the thin 8.6nm shells, perhaps indicating that our previous enhancement problem could simply be resolved by refreshing the stock of nanoparticles more often. After analyzing over twenty 35 nm SCNPs, their average enhancement was 1.29 ± 0.32, which is basically identical to the thin shells. It will be interesting to see the exact characteristics of these new solutions, especially since the slightly thicker 35nm SCNPs seem to be enhancing even more than the alleged 25nm ones.