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Bacteria as nanofactories: silver nanoparticle bioproduction

Bacteria as nanofactories: silver nanoparticle bioproduction
Bacteria as nanofactories: silver nanoparticle bioproduction
Silver nanoparticles (AgNPs) have unique chemical and physical properties which make them attractive in a range of applications. However, current productions methods are often hindered by challenges with poor particle stability, the use of hazardous chemicals under harsh conditions, and challenges with scaleup. Bacteria have been proposed as an alternative production route. However, the underlying biological mechanisms remain to be fully understood. The aim of this project was to develop an environmentally friendly and scalable method for the production of stable AgNPs through the use of bacteria. This project also aimed to improve the understanding of bacterial AgNP production and to gain control over the shapes of AgNPs produced by bacteria. The reaction conditions under which AgNPs were produced by Morganella psychrotolerans were investigated. The conditions examined had little effect on the properties particles being produced, however, the amount of production was affected by Ag+, H+, and Na+ concentrations. Moreover, it was observed that light exposure during synthesis was beneficial to production yields. To investigate this further, M. psychrotolerans was illuminated with LED light for 48 h during AgNP production. The amount of particles produced was considerably higher when samples were exposed to light compared to those in the dark. Moreover, shorter wavelengths of light were determined to be responsible for this increased. It was also discovered that sterile growth media was capable of photo-reducing Ag+ and contributed to the enhanced production. Following this, laser light was used to increase the rate of production further. Spherical AgNPs were produced on the time-scale of seconds rather than hours when reactions were conducted in the dark. This process was thought to be photo-catalytic rather than a thermal process. The foundations of larger scale production were laid when the process of photo-enhanced AgNP bioproduction was translated from batch to flow production. Through the development of a series of flow reactor prototypes, a larger scale reactor was designed, constructed, and operated. The product was a highly concentrated solution of Ag nanospheres. The cause of biogenic AgNPs’ superior stability was probed with proteomic analysis of the corona. The corona appears to be comprised of proteins which are abundant in the supernatant of cultures and can bind sufficient strongly to remain bound to the particle throughout the sample preparation. There does not appear to be an apparent functional connection between the bound proteins. Further investigation is warranted to identify difference in supernatant proteins which were bound to AgNPs and those which were not bound to the particles. This project has increased the knowledge surrounding bacterial AgNPs and flow reactor technology developed in this project will likely be useful in increasing the scale of bacterially stabilised AgNPs.
University of Southampton
Mabey, Thomas Michael
85bd72ae-ada4-4235-b4d9-c80407e6bdc5
Mabey, Thomas Michael
85bd72ae-ada4-4235-b4d9-c80407e6bdc5
Zhang, Xunli
d7cf1181-3276-4da1-9150-e212b333abb1

Mabey, Thomas Michael (2019) Bacteria as nanofactories: silver nanoparticle bioproduction. University of Southampton, Doctoral Thesis, 273pp.

Record type: Thesis (Doctoral)

Abstract

Silver nanoparticles (AgNPs) have unique chemical and physical properties which make them attractive in a range of applications. However, current productions methods are often hindered by challenges with poor particle stability, the use of hazardous chemicals under harsh conditions, and challenges with scaleup. Bacteria have been proposed as an alternative production route. However, the underlying biological mechanisms remain to be fully understood. The aim of this project was to develop an environmentally friendly and scalable method for the production of stable AgNPs through the use of bacteria. This project also aimed to improve the understanding of bacterial AgNP production and to gain control over the shapes of AgNPs produced by bacteria. The reaction conditions under which AgNPs were produced by Morganella psychrotolerans were investigated. The conditions examined had little effect on the properties particles being produced, however, the amount of production was affected by Ag+, H+, and Na+ concentrations. Moreover, it was observed that light exposure during synthesis was beneficial to production yields. To investigate this further, M. psychrotolerans was illuminated with LED light for 48 h during AgNP production. The amount of particles produced was considerably higher when samples were exposed to light compared to those in the dark. Moreover, shorter wavelengths of light were determined to be responsible for this increased. It was also discovered that sterile growth media was capable of photo-reducing Ag+ and contributed to the enhanced production. Following this, laser light was used to increase the rate of production further. Spherical AgNPs were produced on the time-scale of seconds rather than hours when reactions were conducted in the dark. This process was thought to be photo-catalytic rather than a thermal process. The foundations of larger scale production were laid when the process of photo-enhanced AgNP bioproduction was translated from batch to flow production. Through the development of a series of flow reactor prototypes, a larger scale reactor was designed, constructed, and operated. The product was a highly concentrated solution of Ag nanospheres. The cause of biogenic AgNPs’ superior stability was probed with proteomic analysis of the corona. The corona appears to be comprised of proteins which are abundant in the supernatant of cultures and can bind sufficient strongly to remain bound to the particle throughout the sample preparation. There does not appear to be an apparent functional connection between the bound proteins. Further investigation is warranted to identify difference in supernatant proteins which were bound to AgNPs and those which were not bound to the particles. This project has increased the knowledge surrounding bacterial AgNPs and flow reactor technology developed in this project will likely be useful in increasing the scale of bacterially stabilised AgNPs.

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More information

Published date: October 2019

Identifiers

Local EPrints ID: 447822
URI: http://eprints.soton.ac.uk/id/eprint/447822
PURE UUID: 17c3ff89-37ec-4635-8d6a-b926fa8be621
ORCID for Xunli Zhang: ORCID iD orcid.org/0000-0002-4375-1571

Catalogue record

Date deposited: 23 Mar 2021 17:38
Last modified: 17 Mar 2024 06:25

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Contributors

Author: Thomas Michael Mabey
Thesis advisor: Xunli Zhang ORCID iD

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