“…Pure metal NPs using gold (Au), silver (Ag), copper (Cu) and iron (Fe) as matrix are often referred to as the first-generation nanomaterials because they are passive nanostructures that can only be applied to project-specific materials after synthesis. 24 Pure metal NPs are the foremost nanomaterials due to their early discovery and versatility, where different synthesis methods have been developed, including chemical, physical, and biological, such as electrodeposition process, laser ablation, and preparation with bacteria and fungus. 25,26 The substrates of metal oxide NPs mainly include copper oxide (CuO), zinc oxide (ZnO), and iron oxides (FeO, Fe 2 O 3 , Fe 3 O 4 ).…”