Modulating the NanoZyme activity for antibacterial and sensing applications
Creators: name: Karim, Md Nurul
Publisher: name: RMIT University
Year: 2024
Subjects: classificationCode: 310607
subject: Nanobiotechnology

description: Natural enzymes are outstanding biological catalysts that can speed up biochemical reactions by converting substrates into products. Although efficient, the intrinsic drawbacks of enzymes, such as high cost in preparation, purification and storage as well as low operational stability restricts their applications in the industry. To overcome these restrictions, there is a growing interest in developing artificial enzymes with similar functions to natural enzymes. In the last decade, a new dimension of research has emerged where nanomaterials have been recognised as a viable alternative to natural enzymes. These nanomaterials possess intrinsic enzyme-like activity and are more commonly referred to as 'NanoZymes'. Although much progress has been made to explore new NanoZymes for a multitude of applications, few efforts have been made to improve the catalytic efficiency of NanoZymes. Knowing this challenge, this thesis attempts to improve the catalytic efficiency of NanoZymes by changing the morphological characteristics (Chapter III), using light as an external trigger to modulate the NanoZyme activity (Chapter IV) and incorporating the NanoZymes on 3D templates (Chapter V).<br> <br>Chapter III demonstrates the ability of peroxidase-mimic copper sulfide (CuS) nanosheets to efficiently minimise bacterial growth. Firstly, two-dimensional (2D) CuS nanosheets were synthesised using a liquid phase exfoliation approach. The 2D morphology of CuS provides access to a large number of catalytic active sites that accelerates the reaction kinetics through enhanced production of hydroxyl radical, a highly reactive oxygen species (ROS).  This enhanced ROS generation by CuS NanoZyme was used to control the growth of both Gram-negative (Escherichia coli) and Gram-positive (Staphylococcus aureus) bacteria. Furthermore, when challenged with biofilm producing bacteria, the enhanced ROS production effectively broke down existing biofilms as well as prevented new biofilm formation. In a nutshell, this study recognised the importance of nanoparticle morphology to accelerate the catalytic NanoZyme activity. Chapter IV was built upon this knowledge, where the antibacterial activity was controlled by developing a photoactive NanoZyme where the activity could be controlled by using light as a 'trigger'. This is because light offers high spatiotemporal resolution without the need for a physical contact. This chapter describes the synthesis of semiconducting copper oxide nanorods (CuO NRs), where the favourable energy-band structure allows its stimulation by visible light (λ ≥ 400 nm). Light irradiation modulates the peroxidase-mimic catalytic performance of CuO NRs by enhancing its affinity to H2O2, thereby remarkably accelerating the generation of ROS by 20 times. This NanoZyme-mediated enhanced ROS production leads to improved antibacterial performance against Gram-negative bacteria E. coli.<br><br>The use of high concentrations of NanoZymes enhance the catalytic activity in the sensor. But high concentrations of NanoZymes can interference in the visible measurement of the sensor response. This has been recognised as a major limitation in sensor development. This limitation was overcome by developing a free-standing NanoZyme where the active nanoparticles were embedded on to a 3D template. Chapter V outlines the deposition of peroxidase-mimic Ag nanoparticles within the 3D matrix of a cotton fabric to act as a free-standing NanoZyme for the rapid detection of glucose in biological fluids. The ability to immobilize NanoZymes on highly absorbent surfaces allows the catalyst to be removed from the reaction medium, while also allowing a high number of NanoZymes to participate in the reaction. The availability of a high amount of NanoZymes accelerates the catalytic reaction to completion within minutes. The practical applicability of this system was establihsed by detecting glucose in urine samples from a healthy and diabetic person and comparing the results with a commercial glucometer and with a well-known glucose oxidase-peroxidase (GOx-POD) approach which is currently used as the laboratory gold standard.<br>