WFU Physics Colloquium

TITLE: Plasmonic Nanoparticles as Versatile Nanorulers for Sensing Applications: Developing the Nanoparticle-on-mirror Architecture

SPEAKER: Alex Taylor

TIME: Monday December 5, 2016 at 9:00 AM

PLACE: Room 107 Olin Physical Laboratory

The basis of plasmonic sensors is the resonant coupling between the oscillations of free electrons, called plasmons, and incident visible light waves. By confining these oscillations within a nanostructure, the coupling efficiency is enhanced by the creation of localized surface plasmon resonant (LSPR) states. The frequency at which these oscillations occur is dependent upon a number of factors, one of which is the proximity of another plasmonic nanoparticle. The relationship between the frequency of the LSPR oscillations and the distance separating the nanoparticles is called the plasmon nanoruler (PNR). This phenomenon is highly distance dependent - a measurement of the LSPR for a plasmonic nanoparticle allows a researcher to calculate the interparticle separation for length scales well beneath the diffraction limit for visible light. However, even with the enhanced coupling between the nanoparticle and incident light, the signal from a single nanoruler is very dim, and adequate control over many nanorulers is difficult to achieve.

The purpose of the work presented in this thesis is to develop the nanoparticle-on-mirror (NPOM) architecture, which overcomes some of the challenges facing plasmonic nanosensors today by combining the advantages of both top-down and bottom-up synthesis methods. I found that simple optical measurements of large ensembles of nanoparticles in an NPOM device can be understood through theoretical models for plasmon nanorulers, and I was able to detect nanoparticle separations on the order of a single nanometer. Furthermore, I was able to quantify changes in the conformation of thin films of polyelectrolytes induced by solution pH, and identify the individual components responsible. Lastly, by combining all of the lessons learned in the development and construction of these devices I suggest a general form for a NPOM nanosensor, and offer a brief guide for future researchers on how they might be able to apply this architecture in their own research.