Cutting-edge developments in zinc oxide nanoparticles: synthesis and applications for enhanced antimicrobial and UV protection in healthcare solutions

Abstract

This paper presents a comprehensive review of recent advancements in utilizing zinc oxide nanoparticles (ZnO NPs) to enhance antimicrobial and UV protective properties in healthcare solutions. It delves into the synthesis techniques of ZnO NPs and elucidates their antimicrobial efficacy, exploring the underlying mechanisms governing their action against a spectrum of pathogens. Factors impacting the antimicrobial performance of ZnO NPs, including size, surface characteristics, and environmental variables, are extensively analyzed. Moreover, recent studies showcasing the effectiveness of ZnO NPs against diverse pathogens are critically examined, underscoring their potential utility in combatting microbial infections. The study further investigates the UV protective capabilities of ZnO NPs, elucidating the mechanisms by which they offer UV protection and reviewing recent innovations in leveraging them for UV-blocking applications in healthcare. It also dissects the factors influencing the UV shielding performance of ZnO NPs, such as particle size, dispersion quality, and surface coatings. Additionally, the paper addresses challenges associated with integrating ZnO NPs into healthcare products and presents future perspectives for overcoming these hurdles. It emphasizes the imperative for continued research efforts and collaborative initiatives to fully harness the potential of ZnO NPs in developing advanced healthcare solutions with augmented antimicrobial and UV protective attributes. By advancing our understanding and leveraging innovative approaches, ZnO NPs hold promise for addressing pressing healthcare needs and enhancing patient care outcomes.

Fig. 1. TEM images of ZnO-NPs prepared at different annealing temperatures: (a) 500, (b) 600 and (c) 700 °C.

Fig. 2. FE-SEM morphology of ZnO nanoflakes.

Fig. 3. EDX spectrum of ZnO nanoflakes.

Fig. 4. XRD patterns of ZnO samples annealed at different temperatures (a) and an electron microscopic image of a ZnO sample subjected to thermal treatment at a temperature of 400 °C (b).

Fig. 5. SEM images of ZnO nanostructures synthesized at different origin of seed layer: (a) on clear glass, (b) on MS seeds, (c) on ED seeds, (d) on AD seeds. Other parameters were: 0.1 M Zn(NO₃)²⁺ HMTA equimolar solution, t = 3 h, T = 90 °C.

Fig. 6. SEM images of ZnO nanostructures synthesized at different Zn(NO₃)₂⁺ HMTA solutions concentration: (a) 0.0125 M, (b) 0.025 M, (c) 0.05 M, (d) 0.1 M (e) 0.2 M, (f) 0.3 M. Other parameters were AD seeds, t = 3 h, T = 90 °C.

Fig. 7. Typical FE-SEM prepared ZnO samples (a) and (b) hexagonal rods (ZnO-1), (c) and (d) flower-like rods (ZnO-2), (e) and (f) flowers-like prismatic (ZnO-3), (g) and (h) quasi-prismatic (ZnO-4).

Fig. 8. The transmission electron microscopy (TEM) image of ZnO-4 nanostructure.

Fig. 9. XRD patterns of prepared ZnO samples.

Fig. 10. TEM image ZnO NPs (a) SAED pattern of ZnO NPs (b).

Fig. 11. A FE-SEM image.

Fig. 12. Transmission electron microscopy (TEM) image of A. baumannii cultured in the absence (a) and presence (b) of chemically synthesized ZnO-NPs.

Fig. 13. (a) Antiadherence assay and (b) antibiofilm assay using tetracycline as positive control and S. aureus as growth control. The experiment was evaluated based on triplicate results with standard deviation (n = 3, p < 0.05). * indicates a significant difference when compared to the negative control (NB only).

Fig. 14. SEM micrographs of biofilm mass: (a) zinc oxide nanoparticles attached to the S. aureus biofilm, (b) biofilm of S. aureus disturbed after 24 h of treatment with ZnO NPs.

Fig. 15. Confocal microscopy analysis of bacterial biofilms after 24 hours of growth in the presence of zinc oxide (ZnO) or zinc sulfide (ZnS) nanoparticles (NPs). Panel (A) displays representative images of untreated, ZnO-treated, or ZnS-treated biofilms, with bacterial biofilms grown alone or with varying concentrations of NPs. Green fluorescence (SYTO9) highlights bacteria, allowing observation of biofilm thickness and morphology through Z-stack reconstruction. Images captured at ×63 magnification with a scale bar of 200 μm. Insets show scanning electron microscopy (SEM) images of individual bacterial cells at ×100 magnification with a scale bar of 1 μm. Panels (B) to (D) quantify fluorescent intensity per square micrometer (μm²) for biofilms of Staphylococcus aureus, Klebsiella oxytoca, and Pseudomonas aeruginosa, respectively, grown with or without Zn NPs. Data analyzed using ImageJ within a 100 μm × 100 μm region of interest (ROI). Bars represent means, error bars show standard deviations (SDs), symbols denote individual ROIs (n = 20 for S. aureus; n = 25 for K. oxytoca; n = 16 for P. aeruginosa). Asterisks indicate P value significance (*, P < 0.05; ****, P < 0.0001), analyzed using ANOVA with Tukey's post hoc adjustment. “ns” denotes nonsignificant comparisons. Experiments repeated twice, yielding consistent results.

Fig. 16. Scanning electron micrograph of P. aeruginosa isolates: (A) before and (B) after treatment with ZnO-NPs.

Fig. 17. The antibacterial effects, measured by the zone of inhibition (mm), of different concentrations of ZnO NPs. Panels 1, 2, 3, 4 represent concentrations of 10 μg mL⁻¹, 20 μg mL⁻¹, 30 μg mL⁻¹, and the standard, respectively, against various pathogens.

Fig. 18. (a) UV-visible absorption spectroscopic analysis of ZnO–CNF5 hybrid, ZnO + CNF blend, and ZnO NP at 0.1 mg mL⁻¹ and 0.2 mg mL⁻¹ and pristine CNF sample at 0.1 mg mL⁻¹, (b) dispersion stability at a high concentration such as (0.5 mg mL⁻¹) (i) ZnO NP, (ii) pristine CNF, (iii) ZnO + CNF blend and (iv) ZnO–CNF5 hybrid, (c) the whitening effect drop-casted on the glass slide, (d) FE-SEM images of ZnO + CNF blend after dry.

Fig. 19. (a and b) Schematic drawing of the influence of ZnO particle size and incorporation on the CNF surface for the optical properties.

Fig. 20. Optical properties of ZnO NPs: (a) white color of ZnO NPs, (b) UV-visible diffuse reflectance spectra of ZnO NPs (inset: zoomed in spectra in the range from 350 to 500 nm), and (c) plot of [F(R)h_]0.5 against photon energy (hν).

Fig. 21. Light transmittance spectra of PLA and PLA/ZnO NPs composite films.

Fig. 22. UV-Vis spectrum of the prepared ZnO nanorods, exhibiting an absorption peak at 362 nm.