STRUCTURAL AND OPTOELECTRONIC CHARACTERISATIONS OF ZINC OXIDE STRUCTURES FOR ANTIBACTERIAL ACTIVITIES ON SKIN BACTERIA
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Date
2014-09
Authors
LING, CHUO ANN
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Abstract
The main objective for this research work is to investigate the structural and
optoelectronic properties of zinc oxide (ZnO) structures with their correlation on
antibacterial activities against Staphylococcus aureus (S. aureus), Pseudomonas
aeruginosa (P. aeruginosa) and Streptococcus pyogenes (S. pyogenes). Two ZnO
powder samples, one with rod-like (ZnO-Pharma) and the other with plate-like
(ZnO-White) structures, were characterised for their morphological, structural,
optical and electrical properties. The rods structures were 30-120 nm in diameter
and the plates structures were 40-200 nm thick. Electron spectroscopy imaging
showed the different distribution of oxygen and zinc atom on the ZnO structures, that
is higher O:Zn ratio on rods structures whiles lower O:Zn ratio on plates structures.
Using annealing temperature of 700°C, oxygen annealing induced high oxygen
adsorption on ZnO structures surface while nitrogen annealing caused oxygen
desorption on ZnO structures surface. The photoluminescence results revealed
higher green emission from ZnO surface under nitrogen annealing but the oxygen
annealing exhibited adverse effect on green emission. Due to the adsorption and
desorption of oxygen, nitrogen annealing improved the surface conductance by about
60% while oxygen annealing decreased the surface conductance by about 80%.
UVA illumination was found to enhance the surface conductance significantly, up to
6 times compared to non-exposure ZnO. On the other hand, antibacterial responses of ZnO structures were studied
towards S. aureus, P. aeruginosa and S. pyogenes. ZnO-Pharma and ZnO-White
samples exhibited excellent inhibition towards S. pyogenes with the percentage
inhibition above 95%. This phenomenon was probably due to the absence of
catalase, making the bacteria vulnerable to the toxic reactive oxygen species (ROS)
released by ZnO. ZnO-Pharma induced higher inhibition toward S. aureus and P.
aeruginosa than that of ZnO-White because of the smaller particle size of rod
structures compared to plate structures. The antibacterial results showed that
oxygen-treated ZnO exhibited slightly higher growth inhibition on S. aureus and P.
aeruginosa compared with unannealed ZnO. UVA illumination on ZnO causes the
greatest inhibition toward the bacteria where the inhibition of S. aureus increased by
9% (ZnO-Pharma) and 15% (ZnO-White) while inhibition of P. aeruginosa
increased by 48% (ZnO-Pharma) and 32% (ZnO-White). Antibacterial enhancement
by oxygen annealing and UVA illumination was probably due to the activated
release of reactive oxygen species in ZnO suspension. The toxicology level of ZnOPharma
and ZnO-White samples was determined to be less than 0.3 mM from the
cytotoxicity test on L929 mouse fibroblast cell lines. ZnO-Pharma and ZnO-White
calamine lotions were successfully prepared, which showed remarkable antibacterial
response toward three skin bacteria.
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Keywords
OXIDE , ANTIBACTERIAL