Use of nanoscale magnetic ferrites as components of plasmonic sensors for SERS detection of persistent organic pollutants

Abstract

This thesis studies the use of magnetic nanoparticles (NPs) as key-components of a new class of surface-enhanced Raman spectroscopy (SERS) sensors, with the overall goal being the development of sensors for environmental polyaromatic hydrocarbon (PAH) monitoring. As SERS relies on electromagnetic field enhancement, magnetic NPs are a core class of materials which are currently under-utilized in this field, with the vast majority of reports only using them as a moveable handle. As their contribution to SERS enhancement has been thus-far negated, this work aims to study them as the main plasmonic contributor of the surface. A patterned magnetic surface was developed using an external field to create a heirarchical multilayer, where one version uses classic iron oxide NPs (IONPs), and another uses cobalt ferrite NPs (CFNPs). The patterned IONP surface has signal-tonoise ratios of 3 dB, exhibiting excellent signal and also longevity, as IONPs are capped with an inert layer. Analogous CFNPs are synthesized to understand how differing magnetic properties and geometries could change sensor performance. CFNPs are synthesized at different reaction scales, resulting in variation of magnetic parameters and particle geometries, which is correlated with differing performance of the surface once integrated into a sensor. The highest-performing CFNP sensor has signal-tonoise ratios (SNRs) of 4.5 dB, and additionally, the substrates are reusable. As these first versions of magnetic NP surfaces prove very useful in plasmonic applications, this work paves the way to further explore use of magnetic materials for sensing.