Browsing by Author "Du Plessis, Danielle Marguerite"

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    Fabrication and characterization of anti-microbial and biofouling resistant nanofibers with silver nanoparticles and immobilized enzymes for application in water filtration
    (Stellenbosch : University of Stellenbosch, 2011-03) Du Plessis, Danielle Marguerite; Cloete, Thomas Eugene; Dicks, Leon Milner Theodore; Swart, Pieter; University of Stellenbosch. Faculty of Science. Dept. of Biochemistry.
    ENGLISH ABSTRACT: Due to a global lack of access to potable water, a problem particularly affecting people in developing countries and the poor, improvement on existing water purification methods are necessary to provide more cost effective, accessible and efficient methods of water purification. In drinking water systems, biofilms are a potential source of contamination, which can affect the biological stability and hygienic safety of water. In industrial water systems, biofilms can cause corrosion, resistance in flow systems and a decrease in efficiency of membranes. Nanotechnology has been identified as a technology to utilize in water purification problem solving. Alternatives to the use of chemical biocides and antibiotics need to be investigated therefore; the focus of this study was the fabrication and characterization of polymer nanofibers containing silver nanoparticles as biocide and anti-biofouling nanofibers with hydrolytic enzymes immobilized on the surface. The aim of this study was to synthesize and compare poly (vinyl alcohol) (PVA) nanofibers and poly (acrylonitrile) (PAN) nanofibers with silver nanoparticles to determine which type of fiber will be the most appropriate for application in water sanitation. The two types of fibers were to be compared based on morphology, silver nanoparticle content, physical distribution of silver nanoparticles, levels of silver leaching from the fibers in water, which could imply toxicity, and most importantly, anti-microbial efficacy. Back scattering electron images revealed that silver nanoparticles in PVA nanofibers were more evenly dispersed than in PAN nanofibers, but that PAN nanofibers had higher silver nanoparticle content. This was confirmed by energy dispersive X-ray (EDX) analysis. Both PVA and PAN nanofibers containing silver nanoparticles had excellent anti-microbial activity, with PVA nanofibers killing between 91% and 99% of bacteria in a contaminated water sample and PAN nanofibers killed 100%. When investigated by SEM, the biocidal effect of PAN nanofibers containing silver nanoparticles can be observed as morphological changes in the cell walls. Neither PVA nor PAN nanofibers leached silver into water. PVA is a non-toxic and biodegradable synthetic polymer, and PVA-silver nanofibers have excellent anti-microbial activity, making it applicable in water sanitation in an environmental conscious milieu. PAN nanofibers are more conductive to the formation of silver nanoparticles, have higher silver nanoparticle content, allowing the complete sanitation of pathogenically contaminated water samples. PAN nanofibers also have better longevity and strength in water, making it ideal for water filtration and sanitation in higher throughput systems. Furthermore, immobilized enzymes are being investigated as possible alternatives to inefficient conventional methods of controlling and removing biofilms from filtration systems. This study demonstrates the covalent immobilization of two industrial proteases and an amylase enzyme onto polymer nanofibers widely used in filtration membranes. Confirmed by FTIR, these nanofibers were successfully activated by amidination, allowing the covalent immobilization of respectively two serine proteases and an α-amylase onto the fibers. When inspected visually, fibers largely retained their original morphology after activation and enzyme immobilization. Immobilized enzymes were, however visible as aggregated particles on the nanofiber surfaces. The large surface area to volume ratio provided by the nanofibers as immobilization surface, allowed sufficient amounts of enzymes to be immobilized onto the fibers so that all enzymes retained above 80% of the specific activity of the free enzymes. For each of the immobilized enzymes, just below 30% of initial activity was retained after 10 repeated cycles of use. Fibers with immobilized enzymes on their surface did not support the growth of biofilms, as opposed to plain nanofibers, which did support the growth of biofilms. When considering the combined advantages of this effective immobilization process, the robustness of the enzymes used in this study, and their effectiveness against biofilms in their immobilized state, a valuable addition has been made to technology available for the control of biofilm formation on filtration membranes, and could potentially be employed to control biofilm formation in water filtration systems. A combination of anti-microbial and anti-biofouling nanofibers into a single nanofiltration product may prove to be highly applicable in water sanitation systems.