- Title
- Development and assessment of bare and hybrid nanomaterials for the sensing of different analytes
- Creator
- Patel, Vaishwik
- Relation
- University of Newcastle Research Higher Degree Thesis
- Resource Type
- thesis
- Date
- 2023
- Description
- Research Doctorate - Doctor of Philosophy (PhD)
- Description
- Colorimetric biosensors show good potential for the detection of various analytes, including drugs, metals, dyes, pollutants, and others. These sensors have several advantages, including easy fabrication, quick detection, high selectivity and sensitivity, and visual colour-based detection, making them inexpensive and simple compared to other biosensors. The broad applicability of colorimetric biosensors can be utilized to design Point-of-Care (POC) sensors or assays for the detection of important analytes in the fields of environmental protection and disease diagnosis. However, the efficiency of these sensors is highly dependent on the material employed for their fabrication and hence the development of ideal materials for selected analyte detection using optical sensing is highly desirable. Nanozymes, a class of nanomaterials, exhibit properties similar to natural enzymes but can withstand harsh conditions such as high pH and extreme temperatures. With proper modifications, nanozymes have the potential to become low-cost, stable and highly efficient colorimetric biosensors with higher selectivity and sensitivity as compared to enzymes. Cerium oxide nanoparticle (nanoceria) is a promising nanozyme due to its dual oxidation states (Ce3+ and Ce4+) assisted by oxygen vacancies on its surface, which mimic enzyme activity and eliminate the need for external oxidizing agents in analyte detection. Surface modification or hybridization could further enhance the enzyme-like activity and analyte detection ability of nanoceria. Surface functionalisation and hybridisation has also been applied for other materials including mesoporous carbon nitrides (MCN) to explore their enzyme mimetic activity. MCN are a metal-free organic semiconductor with unique electronic and basic characteristics and exhibit mesoporous structure and high specific surface area and surface functional groups. Owing to these features, MCN can serve as a suitable platform for anchoring metal or metal oxide nanoparticles and creating hybrid nanozymes for improved colorimetric biosensing of different analytes. The proposed thesis focuses on the synthesis, functionalisation and characterisation of nano materials including nanoceria with varying oxidation states and copper functionalized and high nitrogen containing MCN (Cu-C3N5) and their application for sensing of different molecules. These functionalized nanostructures exhibit enzyme-mimetic activity for superoxide dismutase (SOD), catalase, oxidase, and peroxidase enzymes, based on their electronic and surface properties, allowing for oxidation and reduction reactions. Presence of prominent enzyme like activity of these materials enables detection of fluoride ions (environmental sensing), glutathione (cancer detection), and glucose (disease diagnosis) with a high detection range. The proposed thesis consists of five chapters. The first chapter focuses on the literature review of various MCN with different structures, nitrogen contents and morphologies, and their applications in sensing. This chapter highlights the research gaps in the synthesis and characterization of various MCN and specifically addresses their role in colorimetric sensing. Among the carbon nitrides, graphitic carbon nitride has shown a wide range of applications in sensing analytes, with major applications in environmental remediation, cancer prognosis, and organ dysfunction. Especially, MCN possess versatile textural, sensing and catalytic properties and are widely used in fields such as catalysis, gas capture, and remediation. The properties of MCNs are majorly dependent on several parameters such as precursors, temperature conditions, and templates which can be appropriately tuned to synthesise several different carbon nitrides with varying nitrogen contents. The recent development of new forms of MCNs with higher nitrogen content, such as C3N5, C3N6, and C3N7, has further expanded their potential into various promising applications. Their application in oxidation-reduction reactions (ORR), batteries and energy generation were highlighted on previous occasions. However, their use in sensing has been limited. The first chapter aims to provide a comprehensive review of recent findings in the synthesis of various MCNs with different nitrogen contents and their potential for photoelectrochemical, optical, and quartz microbalance-based sensing applications. Building upon the findings of the first chapter, which discussed the current limitations in the field of MCN for sensing different analytes, the second chapter aims to overcome those limitations. Previous studies have shown that carbon nitride has a high photocatalytic activity and in the presence of light, it can be used to sense glucose. However, achieving the similar sensing performance in the absence of light has rarely been addressed. To overcome this, high nitrogen containing MCN with a stoichiometry of C3N5 and Cu-C3N5 were synthesized for enhanced enzyme mimetic activity. The functionalization of MCN with Cu and the presence of higher nitrogen content in the framework render the material even more susceptible to enzyme mimetic activity specially peroxidase, even in the absence of light. Using this enhanced peroxidase mimetic activity, it was possible to successfully sense glucose and glutathione within a detection limit of 0.4 mM and 2.0 ppm, respectively. These biomolecules are associated with organ dysfunction and cancer prognosis and therefore the findings of this chapter demonstrate a huge potential of Cu-C3N5 for sensing these significant analytes with a high selectivity and sensitivity. The third chapter focuses on using nanoceria, a prominent nanoparticle in the field of nanozymes, for enzyme mimetic activity to sense different analytes. There are numerous studies demonstrating the various enzyme mimetic activities, such as catalase, SOD, oxidase, and peroxidase, of nanoceria. However, the mechanism behind the oxidase mimetic activity of nanoceria is not yet fully understood. To shed light on this mechanism, we synthesized nanoceria with different oxidation states and evaluated its enzyme mimetic activities. Our findings indicate that these activities are largely dependent on the oxidation state of surface cerium atoms. Once this relationship was established, we utilized the oxidase mimetic activity of nanoceria to sense fluoride ions within a linear range of 1 – 10 ppm effectively. This chapter represents a novel contribution to the field of sensing by being the first study to demonstrate the sensing of glutathione using another analyte, fluoride ion. In presence of fluoride ion, nanoceria can detect glutathione in a detection range of 2.5 – 50 ppm with LOD of 3.8 ppm. This work highlights the potential of nanoceria and its enzyme mimetic activity for sensing a wide range of important analytes. The overall thesis focuses on the use of enzyme mimetic activity of bare and functionalized materials specially nanoceria and MCNs for colorimetric sensing of various analytes. Specifically, the oxidase and peroxidase-like activity of these materials can oxidize the redox- active dyes, which change colour upon oxidation. This change in colour intensity is proportional to the concentration of the analyte, providing a means for sensing. The thesis explains this mechanism and demonstrates its use for sensing of fluoride ions, glucose, and glutathione, which play a role in environmental remediation, organ dysfunction, and cancer prognosis. The fourth chapter of the thesis highlights the concluding remarks and provides the directions for further research in the future. The fifth chapter of the thesis contains the information on the supplementary material for the experimental portion of chapter 2 and 3.
- Subject
- biosensing; mesoporous carbon nitride; cerium oxide; nanomaterial
- Identifier
- http://hdl.handle.net/1959.13/1504831
- Identifier
- uon:55581
- Rights
- Copyright 2023 Vaishwik Patel
- Language
- eng
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| Thumbnail | File | Description | Size | Format | |||
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| View Details Download | ATTACHMENT01 | Thesis | 11 MB | Adobe Acrobat PDF | View Details Download | ||
| View Details Download | ATTACHMENT02 | Abstract | 1 MB | Adobe Acrobat PDF | View Details Download |