A method for making nanoparticles includes the steps of dipping a metal element in a solution that contains metallic ions or ions with a metal, wherein the metal element has a lower electronegativity or redox potential than that of the metal in the ions, and rubbing the metal element to make nanoparticles. Another method for making nanoparticles includes the steps of dipping a metal element in a solution that contains metallic ions or ions with a metal, wherein the metal element has a lower electronegativity or redox potential than that of the metal in the ions, and applying sonic energy to at least one of the metal element and solution. A further method for making copper nanoparticles includes the step of adding ascorbic acid to a copper salt solution.