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A new approach for the optical sensing of contaminants of emerging concern based upon core-shell nanoparticles

Magneto-plasmonic nanostructures are multi-functional materials that promise novel applications for the development of surface plasmon resonance (SPR) sensors. This type of structure combines features of ferromagnetic and noble metals, giving magnetic nanoparticles with outstanding optical properties due to the plasmonic response of noble metals. This study is focused on the development of an optical technique based on a total internal reflection configuration with the use of colloidal core-shell nanoparticles for the sensing of organic pollutants in freshwater. Specifically, nanoparticles with a magnetite core and gold shell (Fe3O4@Au) are used. These nanostructures allow a spectral tunability of their optical response depending on the geometric features of the nanoparticles such as size or shape. As a result, the localized surface plasmon resonance (LSPR) of these nanoparticles can be fine-tuned over a wide spectral domain. For this purpose, finite-difference time-domain (FDTD) simulations were implemented to guide the nanoparticle synthesis and to be able to compare theoretical and experimental results. The magnetic properties allow the facile collection of the nanoparticles from solution as well as the immobilization and concentration of the nanoparticles in presence of a permanent magnet. Simultaneously, the gold shell of these nanoparticles is optically active, which will enable analyte detection via fluctuations of the reflectance curve which occur when molecules bind to the gold surface.