Microwave-assisted green synthesis and computational insights into metal oxide nanoparticles: Focus on ZnO, CuO, and Cu-doped ZnO for biomedical applications - a narrative review

Microwave-assisted green synthesis offers a promising route for preparing metal oxide (MO) nanoparticles (NPs) with potential biomedical applications. This review focuses specifically on ZnO, CuO, and Cu-doped ZnO NPs with the emphasis on the relationship between microwave-assisted green synthesis, material properties, computational analysis, and biomedical performance. The review critically examines the effects of microwave power, irradiation time, precursor concentration, solvent, pH, and biological agents on nanoparticle formation and properties, and compares microwave processing with conventional synthesis routes. Particular attention is given to Cu incorporation in ZnO and its influence on structural, optical, and electronic properties. The biomedical evidence for antimicrobial, anticancer, wound-care, drug-delivery, and related applications is also assessed, together with reported safety concerns and limitations. DFT studies are discussed as a complementary approach for understanding electronic structure, defects, charge distribution, adsorption, and Cu-induced changes. The review shows that microwave-assisted green synthesis can reduce processing time, but variations in synthesis conditions and plant extracts limit reproducibility and direct comparison between studies. Most biomedical evidence remains at the laboratory level, while long-term toxicity, in vivo validation, scale-up, and integration of DFT with experimental studies remain limited. The review identifies these gaps and highlights the need for standardised synthesis, comparable biological testing, and closer experimental computational integration. Microwave-assisted green synthesis enables rapid preparation of ZnO, CuO, and Cu-doped ZnO NPs. Green synthesis reduces conventional chemical use. Cu doping modifies the structural, optical, electronic, and biomedical properties of ZnO. DFT explains electronic structure, defects, and Cu-induced changes. Reproducibility, toxicity, in vivo validation, and scale-up remain key challenges.