Current Research on Zinc Oxide Nanoparticles: Synthesis, Characterization, and Biomedical Applications

Abstract

Zinc oxide nanoparticles (ZnO-NPs) have piqued the curiosity of researchers all over the world due to their extensive biological activity. They are less toxic and biodegradable with the capacity to greatly boost pharmacophore bioactivity. ZnO-NPs are the most extensively used metal oxide nanoparticles in electronic and optoelectronics because of their distinctive optical and chemical properties which can be readily modified by altering the morphology and the wide bandgap. The biosynthesis of nanoparticles using extracts of therapeutic plants, fungi, bacteria, algae, etc., improves their stability and biocompatibility in many biological settings, and its biofabrication alters its physiochemical behavior, contributing to biological potency. As such, ZnO-NPs can be used as an effective nanocarrier for conventional drugs due to their cost-effectiveness and benefits of being biodegradable and biocompatible. This article covers a comprehensive review of different synthesis approaches of ZnO-NPs including physical, chemical, biochemical, and green synthesis techniques, and also emphasizes their biopotency through antibacterial, antifungal, anticancer, anti-inflammatory, antidiabetic, antioxidant, antiviral, wound healing, and cardioprotective activity. Green synthesis from plants, bacteria, and fungus is given special attention, with a particular emphasis on extraction techniques, precursors used for the synthesis and reaction conditions, characterization techniques, and surface morphology of the particles.

Keywords: biological activities; green synthesis; zinc oxide nanoparticles.

Figure 8

Morphology of ZnO nanostructures: (A) needles, rods, and wires; (B) helixes and springs; (C) nanopellets/nanocapsules; (D) flower, snowflake, and dandelion; (E) peanut-like; (F) interwoven particle hierarchy; (G) raspberry, nanosheet/nanoplate; (H) circular/round or sphere-shaped. (Reprinted from [209]; open access under CC BY).

Figure 1

Illustration of the antimicrobial property of ZnO-NPs against the bacterial cell wall. They act as potent antibacterial agents through these possible steps: (1) production of reactive oxygen species (ROS) causing oxidative stress, and membrane and DNA damage leading to bacterial death; (2) dissolution of ZnO-NPs into Zn²⁺ and interference with bacterial enzymes, proteins, and amino acids; and (3) electrostatic interaction between ZnO-NPs and cell membrane, resulting in membrane plasma damage and intracellular content leakage. (Reprinted from [29]; open access under CC BY).

Figure 2

Image illustrating antibacterial efficacy against β-lactam-resistant K. pneumoniae obtained using transmission electron microscopy: (a) ZnO-NPs in the untreated state and ZnO-NPs in the treated state (b–e). Cytoplasmic shrinkage (b) disrupted cell wall and membrane (c), denatured protein shows as a dark electron-dense patch (d), and cytoplasmic spillage (e,f). The blue arrow represents an intact cell wall, the yellow arrow represents a disintegrating cell wall and cell membrane, and the violet arrow represents a denatured protein. (Reprinted from [30]; open access under CC BY).

Figure 3

A schematic representation of cytotoxicity potency of ZnO-NPs leading to the death of cancer cells. ZnO-NPs induce ROS production sequentially, leading to oxidative stress, DNA damage, p53 activation, and apoptosis of cancerous cells.

Figure 4

Mechanism of anti-inflammatory potency of ZnO-NPs.

Figure 5

A diagram showing the effects of metal oxide (e.g., ZnO) coating on the orthopedic implant and bone.

Figure 6

The diagram shows the functions of Zn in stimulating osteoblastic bone formation and mineralization. Zinc stimulates gene expression of various proteins including type I collagen, alkaline phosphatase, and osteocalcin in the cells. Zn is also known to increase the production of growth factors such as IGF-I and TGF-β1 in osteoblastic cells.

Figure 7

Synthesis approaches for ZnO-NPs.