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Browsing by Author "Oliveira, Miguel António Martins de"

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  • Green Synthesis of Silver Nanoparticles from Marine Fungi for Antimicrobial Applications: Preservation of Cultural Heritage
    Publication . Oliveira, Miguel António Martins de; Novais, Sara Calçada; Campos, Maria Jorge Geraldes; Dias, Juliana Rosa
    Nanotechnology is a rapidly expanding field with immense biotechnological potential. Silver nanoparticles (AgNPs) are highly valued for their unique physiochemical and biological properties, although their synthesis conditions can significantly influence these characteristics. Eco-friendly biological methods offer a faster and simpler approach to producing small, stable, and high-yield AgNPs. One promising application of AgNPs is in the preservation of cultural heritage, where recent research has demonstrated their effectiveness in controlling microbial growth and preventing the biodeterioration of valuable historical artefacts. The primary goal of this dissertation was to assess the potential of marine fungi associated with macroalgae for the eco-friendly synthesis of silver nanoparticles, intended as antimicrobial agents for cultural heritage preservation. In the first experimental study, the biosynthesis of AgNPs by cell-free filtrates (CFFs) of eight marine fungal species was evaluated and optimized for nanoparticle size, yield, dispersity, and stability. The use of CFFs from Talaromyces pinophilus, Aspergillus fructus, Purpureocillium lilacinum, Penicillium toxicarium, and Emericellopsis maritima grown under hypo-osmotic conditions (distilled water medium), combined with optimal biosynthesis reaction parameters identified through response surface methodology (pH 10, 100 ºC, 105 min, 1.5 mM AgNO3, and 40% (v/v) CFF), significantly enhanced the production of high yields of predominantly monodispersed AgNPs. The nanoparticles exhibited moderate stability, with a substantial fraction being smaller than 50 nm, except for P. lilacinum which produced larger particles. In the second experimental study, the antibacterial potential of biosynthesised AgNPs was tested against environmental culturable bacteria isolated from mosaic test pieces (MTPs, limestone) exposed in the Roman city of Conímbriga, Portugal. The CFFs, under the previously defined optimized reaction parameters, produced a high yield of polydisperse AgNPs with stable zeta potentials ranging between -20 mV and -40 mV. The AgNPs synthesized by T. pinophilus CFF averaged under 100 nm in size, while the others exceeded 100 nm, but with a significant proportion of small-sized particles. The antibacterial activity of these AgNPs was tested against ten bacterial strains isolated from the MTPs at 25 μg/mL and 6.25 μg/mL. The higher concentration inhibited the growth of nine of the ten isolates, while the lower concentration was effective against three strains. Chryseobacterium sp. exhibited resistance to both concentrations. Additionally, the lower concentration reduced biofilm formation in Janthinobacterium lividum and Microbacterium oxydans, but not in Erwinia persicina. AgNPs synthesised by the CFFs of T. pinophilus and A. fructus showed the greatest antibacterial effectiveness, likely due to their smaller size. In summary, the results of this dissertation highlight the effectiveness and practicality of using marine fungal CFFs to produce AgNPs through an eco-friendly process. These biosynthesised AgNPs demonstrated significant antibacterial properties against bacterial strains that may colonise culturally significant artefacts, underscoring their potential for application in heritage preservation.
    2024-12-03Master thesis Restricted access Show more