ZnO nanorod-chitosan composite coatings with enhanced antifouling properties.

The current study describes the fabrication of chitosan­zinc oxide nanorods composite (CHT/ZnO) on fiberglass panels (support substrate). ZnO nanorods (NRs) with size ranging from 20 to 100 nm and some microrods with an approximate size of 0.5-1 µm were grown on fiberglass panels. CHT 1%/ZnO composite had ZnO NRs incorporated into chitosan (CHT) coating while ZnO NRs were not visible in the CHT 2%/ZnO NRs composite. XRD and FTIR results showed the presence of the ZnO and chitosan. The water contact angle decreased from 80° ± 2° (control) to 65° ± 2° for CHT 1%/ZnO NRs and 42 ± 2° for CHT 2%/ZnO NRs composite coatings. The antimicrobial activities of the coated fiberglass panels were investigated using biofilm-forming bacteria Bacillus subtilis and Escherichia coli under both light and dark conditions. CHT/ZnO composite coated fiberglass panels showed the strongest antimicrobial activity compared to chitosan, ZnO NRs coatings, and Zn-based antifouling paint in the experiments with B. subtilis and E. coli under light conditions. The highest antifouling activity was observed for CHT 2%/ZnO composites. CHT/ZnO composites can be good alternatives to the toxic antifouling paints.

Nanocomposite Zinc Oxide-Chitosan Coatings on Polyethylene Films for Extending Storage Life of Okra (Abelmoschus esculentus).

Efficiency of nanocomposite zinc oxide-chitosan antimicrobial polyethylene packaging films for the preservation of quality of vegetables was studied using okra Abelmoschus esculentus. Low density polyethylene films (LDPE) coated with chitosan-ZnO nanocomposites were used for packaging of okra samples stored at room temperature (25 °C). Compared to the control sample (no coating), the total bacterial concentrations in the case of chitosan and nanocomposite coatings were reduced by 53% and 63%, respectively. The nanocomposite coating showed a 2-fold reduction in total fungal concentrations in comparison to the chitosan treated samples. Results demonstrate the effectiveness of the nanocomposite coatings for the reduction of fungal and bacterial growth in the okra samples after 12 storage days. The nanocomposite coatings did not affect the quality attributes of the okra, such as pH, total soluble solids, moisture content, and weight loss. This work demonstrates that the chitosan-ZnO nanocomposite coatings not only maintains the quality of the packed okra but also retards microbial and fungal growth. Thus, chitosan-ZnO nanocomposite coating can be used as a potential coating material for active food packaging applications.

Living on the edge: biofilms developing in oscillating environmental conditions.

For the first time, the densities and diversity of microorganisms developed on ocean gliders were investigated using flow cytometry and Illumina MiSeq sequencing of 16S and 18S rRNA genes. Ocean gliders are autonomous buoyancy-driven underwater vehicles, equipped with sensors continuously recording physical, chemical, and biological parameters. Microbial biofilms were investigated on unprotected parts of the glider and surfaces coated with base, biocidal and chitosan paints. Biofilms on the glider were exposed to periodical oscillations of salinity, oxygen, temperature, pressure, depth and light, due to periodic ascending and descending of the vehicle. Among the unprotected surfaces, the highest microbial abundance was observed on the bottom of the glider's body, while the lowest density was recorded on the glider's nose. Antifouling paints had the lowest densities of microorganisms. Multidimensional analysis showed that the microbial communities formed on unprotected parts of the glider were significantly different from those on biocidal paint and in seawater.

Chitosan-zinc oxide nanocomposite coatings for the prevention of marine biofouling.

Marine biofouling is a worldwide problem affecting maritime industries. Global concerns about the high toxicity of antifouling paints have highlighted the need to develop less toxic antifouling coatings. Chitosan is a natural polymer with antimicrobial, antifungal and antialgal properties that is obtained from partial deacetylation of crustacean waste. In the present study, nanocomposite chitosan-zinc oxide (chitosan-ZnO) nanoparticle hybrid coatings were developed and their antifouling activity was tested. Chitosan-ZnO nanoparticle coatings showed anti-diatom activity against Navicula sp. and antibacterial activity against the marine bacterium Pseudoalteromonas nigrifaciens. Additional antifouling properties of the coatings were investigated in a mesocosm study using tanks containing natural sea water under controlled laboratory conditions. Each week for four weeks, biofilm was removed and analysed by flow cytometry to estimate total bacterial densities on the coated substrates. Chitosan-ZnO hybrid coatings led to better inhibition of bacterial growth in comparison to chitosan coatings alone, as determined by flow cytometry. This study demonstrates the antifouling potential of chitosan-ZnO nanocomposite hybrid coatings, which can be used for the prevention of biofouling.