Green nanotechnology-based zinc oxide (ZnO) nanomaterials for biomedical applications: a review

The rise of nanotechnology has brought to the world a new potential and broader perspective of what humanity can achieve through material manipulation at the nanoscale. As a consequence, the use of different nanomaterials has revolutionized both the industrial and biomedical worlds. Metallic and metal-oxide nanostructures have shown great potential due to their high surface to volume ratio and high reactivity. Among them, zinc oxide (ZnO) has revealed wider applicability, including in nanomedicine, where ZnO nanomaterials have shown great potential leading to effective interactions with biological membranes and exhibiting antibacterial and/or anticancer behaviors. However, consistent with several other nanostructures, the synthesis of ZnO nanomaterials is not devoid of drawbacks, such as the production of harmful and toxic byproducts, the use of toxic reagents, the employment of expensive instruments, and the lack of biocompatibility, all of which need to be overcome before extensive use. As a solution, green nanotechnology has allowed the production of ZnO nanostructures using environmentally friendly and cost-effective methods, which are based on the use of living organisms, natural biomolecules and waste materials. Once produced, green-synthesized ZnO nanoparticles have shown enhancements in terms of their cytocompatibility and biomedical properties compared to their traditionally produced counterparts, becoming excellent antibacterial or anticancer agents. These ZnO nanoparticles have also proven to be valuable materials in combination with wound healing processes and biosensing elements in order to trace small amounts of biomarkers associated with different diseases. As a consequence, there is a synergy between green nanotechnology and ZnO nanomaterials, which is leading to an exciting flourishment in the field, presenting a wide variety of biomedical applications for these nanostructures. This review compares and contrasts recent approaches and examples of the use of green-synthesized ZnO nanomaterials with traditionally synthesized structures, demonstrating a remarkable potential for their use as a powerful biomedical agent.