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Title: Continuous flow synthesis of gold nanoparticles in microfluidic systems for SERS and antimicrobial applications
Author: Huang, He
Awarding Body: UCL (University College London)
Current Institution: University College London (University of London)
Date of Award: 2019
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In this thesis we focus on the synthesis of gold nanoparticles (Au NPs) which are mainly used for the Surface Enhanced Raman Scattering (SERS) and antimicrobial applications. As the properties of Au NPs are morphology-dependent, synthetic routes with good control are quite important to obtain the Au NPs with best performance during applications. The aim of this thesis was to investigate the adaptation of different synthetic routes of Au NPs from batch to continuous microfluidic systems to overcome some shortcomings in batch and achieve controllable fabrication. Firstly, sub-3 nm citrate-capped gold nanoparticles were synthesized in continuous flow capillary reactors with enhanced nucleation for easier further functionalization compared to thiol-capped Au NPs in similar size range. It is speculated that the negatively charged tubing-water interface, offers heterogeneous nucleation sites for positively charged citrate-gold precursor species, stabilizing the nuclei and inhibiting their growth. As a gaseous reducing agent, carbon monoxide (CO) has a big potential in nanoparticle synthesis as it is very easy to remove from the product. The second synthetic route was the synthesis of Au NPs by CO reduction in microfluidic system. With the aid of segmented microfluidic system, the polydispersity of Au NPs was reduced to < 5% compared to Au NPs with similar size synthesized in a batch system (11%). The CO-produced gold nanoparticles without any capping agent (26.6 nm) showed a good SERS performance with an average enhancement factor of 2.40 × 109 which were contributed by the narrower gap between particles and easier adsorption of analysing molecule onto naked surface of gold nanoparticles. To improve hydrodynamics, CO-aqueous gold precursor flow system was changed by using a Teflon AF-2400 membrane contactor in a tube-in-tube set-up to pre-dissolve CO into organic phase at higher pressure. Since more concentrated CO enhanced the reduction rate, capping agent was important to obtain stable Au NPs with different sizes. After optimization, cysteine was chosen as the capping agent to develop a rapid (3 min compared to few hours ~ days in batch) and high-yield (yield > 95%, throughput ~ 50 mg/h) synthesis of Au25(Cys)18 nanoclusters (NCs) via CO reduction in segmented microfluidic system. These Au NCs as a crystal violet (CV) photobactericidal enhancement agent was tested against S. aureus, which showed significantly enhanced bactericidal activity of crystal violet encapsulated in a silicon substrate under white light illumination of ~312 lux.
Supervisor: Gavriilidis, A. ; Parkin, I. Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available