title: Plasmonic nanostructures for molecular sensing and colour filtering
Creators: name: Sperling, Justin Ryan
Publisher: name: University of Glasgow
Year: 2019
Subjects: subject: Plasmonics, nanofabrication, sensors, biosensor, LSPR, SPR, high-resolution, optics, nano-pixel, colour, whisky, PCA, surface chemistry.

description: Plasmonic nanoarrays offer a number of advantages over other technologies when it comes to optical sensing and colour filtering—namely their full tunability across the visible spectrum, high sensitivity to local refractive index changes, relative stability, and ultra-high resolution. For optical sensors, as their use progresses towards portable devices capable of rapid and highly-specific sensing, reduction in complexity, device size, and data acquisition time is key; and for optical colour filtering and encoding, the desire for long-term-stability and ultra-high resolution is key. One way to achieve the aforementioned goals in both fields is through the development of optical devices capable of producing two signals/displays within one region. This thesis explores the fabrication and characterisation of such devices for applications in molecular sensing and colour display technologies. First, a proof-of-concept device consisting of two nanoplasmonic arrays arranged in a multilayer configuration is explored. This device is demonstrated capable of self-correcting for drift by simultaneously obtaining both sensing and reference signals from a single measurement without complex optics or multiple sensing regions. This is design holds promise for point-of-care diagnostics, where data acquisition occurs over extended periods of time and measurement stability due to the external environment may be problematic. Next, another method of arranging two plasmonic nanoarrays is examined. These devices consist of superimposed aluminium and gold nanoarrays with modified surface chemistries resulting in a bimetallic device which produces two distinct resonance peaks for each sensing region. When combined, the signals from the different arrays are demonstrated capable of discriminating between organic solvents and between whiskies using trained pattern recognition. As each element in the bimetallic optical tongue produces two partially-selective measurements (rather than the one measurement capable with comparable devices), the proposed sensor is capable of halving device size and data-acquisition time. This advance in miniaturisation and multiplexed readout would be highly useful in areas that rely on assays for determining if a mixture is within tolerance, such as the medical, food &amp; drug, and security industries. Then, a new approach to high-density image encoding is demonstrated using full-colour, dual-state nano-pixels, doubling the amount of information that can be stored in a unit area. The smallest readable ‘unit’ using a standard optical microscope relates to 370 nm x 370 nm. As a result, dual-state nano-pixels may prove significant for long-term, high-resolution optical image encoding, and counterfeit-prevention measures. Finally, a combination of plasmonic sensing with the dual-state capabilities of the nano-pixel design presented is investigated. The dual-state capabilities of the nano-pixel design will allow trapping of biomolecules with one arm while simultaneously, yet independently, sensing with the other. While only preliminary work is covered, once successfully developed, such devices will aid the understanding of proteins and thus benefit the fields of biology, chemistry, medicine, and pharmacy. Additionally, they will allow for the testing and creation of new disease screenings and drug therapies.