In the present study, green synthesis of silver nanoparticles (AgNPs) was conducted to prepare a preservative solution for organic bamboo straws. Spherical AgNPs were prepared with the help of ultrasound waves by inducing a reaction between silver nitrate (AgNO3) solution (0.05 M) and tea leaf extract (Camellia sinensis). Spherical AgNPs with an 11–28 nm size were formed easily in the extract at ambient temperature. The as-prepared AgNPs–chitosan solutions exhibited excellent antifungal activity against Aspergillus flavus fungi, which were isolated from bamboo straws collected from the Nam Dong district of Thua Thien Hue province in Vietnam. Therefore, the AgNPs–chitosan solution can be used as a bamboo-straw-coating material to inhibit the growth of A. flavus fungi. The optimized concentrations of AgNPs and chitosan to achieve the antifungal activity of AgNPs–chitosan solution on bamboo straws were 40 parts per million and 1.5%, respectively. Thus, coating bamboo straws with this solution can be proposed as an additional treatment to increase their postharvest quality. Moreover, AgNPs–chitosan solution can be used to protect bamboo straws from fungal infections, thereby prolonging their shelf life.

This study presents a novel process to synthesize curcumin nanoparticles from fresh turmeric. An ultrasonic-assisted cajeput oil in water emulsion technique was used to synthesize nanocurcumin. The prepared nanocurcumin was spherical with an average size of 47 nm and size distribution of 5–80 nm. The synthesized nanocurcumin showed improved aqueous-phase solubility, and it was used as a reducing agent and stabilizer for biosynthesizing silver nanoparticles. Furthermore, the X-ray diffraction pattern of the silver nanoparticles showed four distinct diffraction peaks at 38.3°, 44.6°, 65.1°, and 78.1° corresponding to the lattice planes of face-centered cubic silver ((111), (200), (220), and (311)). Transmission electron microscopy analysis indicated the average size and maximum size distribution (80 %) of the silver nanoparticles were 10.9 nm and 5–15 nm, respectively. UV–visible spectroscopy measurement of samples indicated the localized surface plasmon resonance absorbance of an aqueous dispersion of silver nanoparticles at 406 nm. Zeta potential analysis revealed a negative charge with a magnitude of −27.2 mV, which indicated higher aqueous dispersion stability of the silver nanoparticles prepared from nanocurcumin. The nanoparticles showed antibacterial activity against Vibrio parahaemolyticus.

The synthesis, characterization and application of biologically synthesized nanomaterials have become an important branch of nanotechnology. In the present study, we report the synthesis of silver nanoparticles from fresh leaf extract of Centella asiatica (LEC). UV-Vis spectrum for silver colloids contains a strong plasmon band near 425[Formula: see text]nm, which confirms the formation of nanoparticles. The experimental results show that the silver nanoparticles are formed easily in the extract at ambient temperature. The resulting silver nanoparticles (AgNPs) were in the spherical form and the average size of the nanoparticles was in the range from 3[Formula: see text]nm to 30[Formula: see text]nm. From the above silver nanoparticles, we were taken up to investigate the effects of various concentrations of AgNPs on growth, development and yield of peanut plants. The results of the present experiment showed that the optimized concentration of AgNPs of the good germination, growth and pod yield of peanut plant is 5[Formula: see text]ppm.

Mandarin (Citrus deliciosa Tenore) is one of the most important fruit crops grown in the Hue province, Vietnam, and has immense economic, health and cultural significance. However, mandarins are highly perishable and more susceptible to diseases compared to other citrus fruits. In the present study, biomimetic synthesis of silver nanoparticles (AgNPs) for preparing preservative solutions for mandarins was investigated. Spherical and nanometer-sized AgNPs that were prepared with the help of ultrasound wave induced a reaction between silver nitrate solution (AgNO3 0.02[Formula: see text]M) and the leaf extract of Centella asiatica. Spherical AgNPs were formed easily in the extract at an ambient temperature and their average size ranged from 3[Formula: see text]nm to 30[Formula: see text]nm. These AgNPs exhibited potent antifungal activity against Macrophoma theicola B1 fungi, which were isolated from mandarin peels collected from agricultural lands of rural villages of Thua Thien-Hue province in Vietnam. Thus, we are successful in preparing an AgNPs-containing preservative solution as a mandarin fruit-coating material to inhibit the growth of M. theicola B1 fungi. The coating of mandarin fruits with this preservative solution prolonged the storage life of the fruits from 9 to 35 days. On the 35th day, the preserved fruits maintained their natural color and ripening, whereas the control sample decayed with white fungus covering its skin after 9 days of storage. Thus, coating mandarins with this solution can be proposed as an additional treatment for increasing their postharvest quality. Additionally, it can be a solution for protection against fungal infection and physiological damage and controlling the decay of mandarins, thereby prolonging their shelf life.

No abstract