| dc.description.abstract | For the past few decades, nanomaterials have been an integral part of research involving applications in various industries, ranging from pharmaceuticals, electronics, energy, chemical, food, aviation, etc, owing to their unique optical, magnetic, mechanical, electrical, and other physico-chemical properties...Two research areas in particular, where nanomaterials have found an increased interest are environmental and biomedical sciences, as hydrological tracers and drug delivery systems, respectively. The main focus of this thesis is to synthesise, functionalise and characterise magnetic and polymeric nanoparticles (NPs) for the potential use as hydrological tracers, drug delivery systems and biosensors. The use of tracers has been well established to monitor and manage hydrological systems such as brooks, streams and rivers...However, the availability of a limited number of potential tracers such as salts, isotopes and dyes, makes studies of hydrological processes a challenge. Furthermore, traditional tracers find limited use due to the lack of multiplexed, multipoint tracing and background noise, among others...In this regard, DNA-based tracers possess remarkable advantages including, being environmentally friendly, stable, and with high sensitivity, in addition to showing great potential in providing an ideally unlimited number of unique tracers capable of multipoint tracing.-Though some studies present magnetic DNA-based tracers for hydrological applications, these utilise a single type of DNA to functionalise one type of iron-oxide NP (IONP). Therefore, there exists a gap in research that could show the possibility to produce multiple magnetic tracers by functionalising different IONPs with different DNA. Additionally, there are no reports investigating the variation of magnetic properties of the tracers with the functionalisation process. In this work, DNA-based tracers aimed at hydrological applications were developed. To make the tracers magnetic, to facilitate recovery, IONPs were incorporated in the core of the tracers.-These IONPs were synthesised using co-precipitation and thermal decomposition techniques that yielded particles with sizes ranging from 9 to 20 nm, spherical and cube shaped, with different physico-chemical properties.-Particle size and shape, among other factors, have a crucial role in determining the magnetic properties of the tracers and in turn their magnetic harvesting for separation and analysis. Synthesising IONPs via thermal decomposition enables precise control over the particle’s size, morphology, and eventually, their magnetic properties.-Time-based growth for IONPs, synthesised via thermal decomposition of iron-oleate precursor, showed that iron-oleate started to decompose around 300 ◦C following burst nucleation and the reaction subsequently entered growth regime with a rapid increase in particle numbers at 310 ◦C. The reaction stabilised at 320 ◦C, where the particles underwent changes in morphology, owing to surface diffusion and Ostwald ripening.
The surface of IONPs was further modified with selected ligands to vary surface charge and hydrophilicity.–Tetramethyl ammonium hydroxide and sodium citrate provided negative surface charges resulting in zeta potentials of -10 to -50 mV, while cetyltrimethylammonium bromide imparted a positive zeta potential (+30 mV). Thereafter, IONPs were functionalised with trimethoxysilylpropyl–N,N,N–trimethylammonium chloride, before DNA functionalisation, to provide a positive surface potential (>13 mV) that facilitated DNA binding.-Thereafter, the IONPs were functionalised with three different double stranded DNA (T21, GM5 and GM6) to explore the possibility of producing multiple tracers, each having its unique tag.-A subsequent coating of silica, encapsulated and protected the DNA from loss to the surroundings. Magnetic characterisation showed high saturation magnetisation (>75 emu/g) for the IONPs after each functionalisation step. Further, the IONPs were used for biosensing applications, utilising the concept of magnetophoresis — motion of magnetic particles in a constant magnetic field gradient. IONPs were coupled with silver NPs that impart optical characteristics of localised surface plasmon resonance, resulting in dual magneto-plasmonic properties, into dimeric NP (DNP)...Time based growth studies showed that silver nucleated heterogeneously on multiple sites on the IONP surfaces in the initial stages of the reaction, forming satellite/raspberry-like morphology.–As the reaction proceeded, the particles attained a dumbbell-like shape due to the reorganisation of silver resulting from surface diffusion and Ostwald ripening...Furthermore, the effect of the silver precursor (silver acetate) concentration on the physico-chemical properties of DNPs showed increased plasmonic response and decreased magnetisation with increasing concentration...Time-based magnetic separation studies (using the concept of magnetophoresis) showed the potential of DNPs to be used as sensors...Two separate particle populations were obtained after exposing the particles to the magnetic field for 24 h. Larger particles separated after ∼10 h showing greater separation velocities, while the smaller particles had longer separation times. By analysing separation times for different particle populations in different samples, the presence of target analyte can be detected. Another field, where NPs find immense use in medicine, is cancer treatment, as NP-based targeted drug delivery systems aid in reducing spread of drug toxicity to the healthy tissue, thereby increasing the effectiveness of the delivered drug in killing cancer cells...Stimuli-responsive NGs have received interest, due to their ability to swell or collapse in accordance with changes in stimuli such as temperature, pH, ionic strength, light, and electric and magnetic fields. Poly(N-isopropylacrylamide)-co-poly(acrylic acid)-based stimuli-responsive NGs, that possessed both temperature and pH-based stimuli response, were synthesised in this work, with hydrodynamic size ranging from 120 to 400 nm. NGs are usually synthesized using precipitation polymerization at temperatures above the volume phase transition temperature (VPTT) of the formed NG and these reactions are extremely sensitive to synthesis parameters, including, reactant concentrations, surfactant concentration, amount of initiator and reaction temperature.-There exists a gap in research investigating the effect of oxygen in the reaction atmosphere on the synthesis of pNIPAm-pAAc-based NGs.-The growth of NGs was studied via three different synthesis routes, exploring different reaction parameters, namely, surfactant amount (sodium dodecyl sulphate), reaction atmosphere (continuous and intermittent N2 atmosphere) and stirring modes (magnet bar and impeller).-A decrease in NG size was observed using continuous flow of N2, compared to the ones where N2 was introduced at the time of initiator addition...NGs prepared under continuous N2 environment had a lower polydispersity index (0.2) than the ones prepared in an intermittent N2 environment (0.6 - 0.7). The size of the NGs increased (35 to 85 % decrease in hydrodynamic size) on decreasing sodium dodecyl sulphate concentration from 4.2 to 2.1 mM.
To understand the stimuli response from temperature and pH, it is important to study the extent of incorporation of pNIPAm and pAAc in the NG matrix. Most studies investigating this are not associated with NGs, but microgels, and they do not highlight, in detail, the effect of pAAc on the physico-chemical properties of the NGs...Hence, to address this, as well as, to exploit the fact that the cancer region has an acidic microenvironment, the effect of pH response of the NG has been investigated by varying pAAc content in the NG. The size of the NGs increased (230 to 400 nm) with increasing AAc concentration from 10 to 30 mole%. Additionally, the NGs showed increased pH-based collapse (measured at synthesis and pH = 3.5) with increasing pAAc concentration from 10 mole% (6.8 % collapse) to 25 mole% (51.3 % collapse). Furthermore, loading and release studies were performed at different conditions of temperature and pH, using a model protein drug, cytochrome C (Cyt C). High loading (L.E. = 87.4 %) and encapsulation (E.E. = 254.5 µg/mg) efficiencies were measured for NGs synthesised in a continuous N2 environment, whereas, NGs that were prepared in an intermittent N2 environment showed low L.E. (30.8 %) and E.E. (181 µg/mg). Biocompatibility studies, conducted on the NGs using a whole blood model, showed excellent cell viability. The NGs did not activate the complement system and induced little or no release of pro-inflammatory cytokines/chemokines, suggesting good biocompatibility and potential as a candidate for drug delivery vehicles. Both, inorganic and polymeric NPs have been produced in this work employing various synthesis techniques...One of the major challenges faced in the world of nanoscience is reproducibility of NP synthesis...High reproducibility is crucial to ensure similar production batches, thereby reducing any significant deviations in particle quality. The issue of repeatability and reproducibility was faced in this work as well, particularly with particle synthesis and functionalisation...NP quality was examined using various characterisation techniques and measurements were repeated to reduce deviation during analysis...Additionally, multiple sets of experiments were performed and optimised to reduce any undesired uncertainties...The physico-chemical properties of the NPs studied in this thesis, were mapped using a wide array of characterisation techniques...NP sizes have been measured using transmission electron microscopy and dynamic light scattering, while the zetasizer was used for measuring particle surface charge (zeta potentials)...IONP surface functionalisation was measured using attenuated total reflection-Fourier transform infrared spectroscopy and the magnetic properties were investigated using a superconducting quantum interference device and vibration sample magnetometry. Ultraviolet visible spectrophotometry was used for studying the loading and release of Cyt C from NG. To examine successful functionalisation and encapsulation of the DNA with the IONPs and in silica, respectively, quantitative polymerase chain reaction analysis was conducted. This work aimed at providing NPs that have the potential to be used in the applications of hydrological tracing and targeted drug delivery...Thus, the NPs studied within this work provide a contribution to the ever expanding search for unique materials for environmental and biomedical applications. | en_US |
