Antibacterial Activity of Zinc Oxide Nanoparticles Loaded with Essential Oils

Abstract

One major problem with the overuse of antibiotics is that the microorganisms acquire resistance; thus the dose must be increased unsustainably. To overcome this problem, researchers from around the world are actively investigating new types of antimicrobials. Zinc oxide (ZnO) nanoparticles (NPs) have been proven to exhibit strong antimicrobial effects; moreover, the Food and Drugs Administration (FDA) considers ZnO as GRAS (generally recognized as safe). Many essential oils have antimicrobial activity and their components do not generate resistance over time. One of the drawbacks is the high volatility of some components, which diminishes the antimicrobial action as they are eliminated. The combination of ZnO NPs and essential oils can synergistically produce a stronger antimicrobial effect, and some of the volatile compounds can be retained on the nanoparticles’ surface, ensuring a better-lasting antimicrobial effect. The samples were characterized with X-ray diffraction (XRD), transmission electron microscopy (TEM), scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FTIR), ultraviolet-visible spectroscopy (UV-Vis), and thermal analysis (TG-DSC) coupled with analysis of evolved gases using FTIR. The ZnO NPs, with a size of ~35 nm, exhibited a loading between 1.44% and 15.62%—the lower values were specific for limonene-containing oils (e.g., orange, grapefruit, bergamot, or limette), while high values were obtained from cinnamon, minzol, thyme, citronella, and lavender oils—highlighting differences among non-polar terpenes and alcohol or aldehyde derivatives. The antibacterial assay indicated the existence of a synergic action among components and a high dependency on the percentage of loaded oil. Loaded nanoparticles offer immense potential for the development of materials with specific applications, such as wound dressings or food packaging. These nanoparticles can be utilized in scenarios where burst delivery is desired or when prolonged antibacterial activity is sought.

Obtaining and Characterizing New Types of Materials Based on Low-Density Polyethylene and Thermoplastic Starch

“…As all the samples contain LDPE, absorption bands at 2915 cm −1 and 2848 cm −1 (Figure 3) can be noticed. These are attributed to asymmetric and symmetric stretching vibrations of the methylene group [53]. The intensity of these two bands is higher than in the TPS sample as they are related to the presence of LDPE in the sample.…”

Chitosan-Supported ZnO Nanoparticles: Their Green Synthesis, Characterization, and Application for the Removal of Pyridoxine HCl (Vitamin B6) from Aqueous Media

“…The ZnO NPs and ZnO/CS composite were initially characterized using a uv-vis spectrometer in the range of 200–800 nm. As shown in Figure 2 , a broad band at 350 nm was detected for the ZnO NPs; this large absorption band is generated due to the electron jump from the valence band to the conduction band, which is mainly because ZnO is a direct-band-gap semiconductor with a wide band-gap [ 23 ]. According to previous reports, ZnO NPs possess a distinct absorption band in the range of 280–400 nm [ 24 ].…”

Anti-Bacterial Activity of Green Synthesised Silver and Zinc Oxide Nanoparticles against Propionibacterium acnes

“…The green synthesised Ag-NPs and ZnO-NPs were characterised using a UV-Vis spectrophotometer in the wavelength range 800–200 nm. As both Ag-NPs and ZnO-NPs are direct bandgap semiconductors, with a wide bandgap of ~3.37 eV between the conduction and the valence bands [ 52 ], the electron jump from the valence band to the conduction band generates an absorption peak between 450 and 500 nm, and between 350 and 450 nm, respectively. The UV-Vis spectrum shows a large absorption peak at approximately 460 nm for Ag-NPs, and at 399 nm for ZnO-NPs ( Figure 1 ).…”