In these two articles we worked with Queen’s researchers Carlos Escobedo and Juan Gomez-Cruz on a new chemical sensor using surface plasmon polaritons. Following earlier work by Escobedo’s group we recorded the “extraordinary optical transmission” through a gold film that has a grid of nanometer-sized holes and monitored its change as the refractive index of an attached polymer film changes. The sensor worked so well that the data gave new insights on the diffusion kinetics of an aromatic compound into that film. Read more about this in Analyst, 2026, DOI: 10.1039/d5an01181g, (link)
In developing a model of the diffusion kinetics that governs the refractive index change we found a major gap in our (and not just “our”) understanding of diffusion kinetics in general. A second article deriving the kinetics from an exact integration of Fick’s Law leads to complicated but exact equations that can be used to model any 1-dimensional diffusion process. The associated article can now be found at Soft Matter, 2026, DOI: 10.1039/D5SM01209K (link)
Exciting stuff: This work formed was an important part of Dr Swapnil Daxini’s PhD dissertation!
The diffusion of o-xylene int to the polymer film increases the refractive index. of the polymer. These refractive index measurements allow us to determine the o-xylene concentration and its change. The curves show clear evidence for a two-step diffusion process that happens at two different rates.