Fong, Yu Man Mandy; (2023) Development of copper nanocomposite coatings for all-optical ultrasound bioimaging. Doctoral thesis (Ph.D), UCL (University College London).

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Abstract

This thesis details the development of air-stable and photostable copper nanoparticles and, subsequently, elastomeric nanocomposite coatings by focusing on three key areas: 1. Development of copper nanoparticle synthesis routes in an ambient environment; 2. Developing organic dye nanocomposites with specific optical absorption properties; and 3. Optimizing fabrication conditions of the elastomeric component – Polydimethylsiloxane (Sylgard 184). By varying synthesis parameters, such as capping agent, copper precursors, synthesis temperature and solvent, a range of particle morphologies was synthesised, including nanocubes (15 ~ 500 nm), nanospikes (average 150 nm in length) and sub 10 nm nanoparticles. These colloidal copper nanoparticles demonstrated good stability, with representative studies indicating stability for at least one month when stored in a dark ambient environment. These copper nanoparticles were fabricated into elastomeric composites via doctor-blading. The majority of these nanocomposites were of sub-100 microns in thickness and measured at over 98% absorption. Further work entailed incorporating a range of cationic and anionic organic dyes into polymeric nanocomposites to shift and enhance absorbance at specific wavelengths, including observational studies of the interaction of dyes with gold and copper nanoparticles. Due to their high optical absorption and the ability to be applied onto a wide range of substrates, these nanocomposites are well suited to an emerging biomedical imaging modality, all-optical ultrasound (OpUS), where they undergo rapid localised heating, which causes a pressure rise that propagates as an ultrasound wave upon pulsed laser excitation. The OpUS performance of the copper nanocomposite coatings was characterised using pulsed (ns-scale) laser excitation at 532 nm. Ultrasound peak-to-peak pressures higher than 2 MPa were achieved with a laser fluence of ~50 mJ/cm2, a conversion efficiency that favourably compares to literature values. Moreover, these nanocomposites demonstrated good photostability, with stable ultrasound pressures after 30 minutes of continuous exposure to laser (laser fluence: 36 mJ/cm2).

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