The invention provides metal-ascorbic acid crystals and a method for synthesizing the metal-ascorbic acid crystals. The metal in the metal-ascorbic acid crystals is one of copper (Cu), gold (Au) and silver (Ag). The method for synthesizing the metal-ascorbic acid crystals includes sonicating a solution of ascorbic acid and a solvent in dark to obtain a clear solution, wherein the solvent is one of dimethylformamide (DMF) and dimethyl sulfoxide (DMSO). A metal salt is added to the clear solution, wherein the metal salt is one of copper (II) sulfate pentahydrate (CuSO4.5H2O), gold (III)-chloride (AuCl3), and silver sulfate (Ag2SO4). The clear solution is sonicated after adding the metal salt to obtain a reaction mixture. Thereafter, the reaction mixture is heated in dark. The reaction mixture is treated to facilitate solvent extraction of the metal-ascorbic acid. Finally, the metal-ascorbic acid is crystallized.