A general method is proposed to synthesize ultrafine nanoporous Cu, Ag, andNi with novel sponge-like morphologies, high porosities, and large surface areas.The materials are produced by dealloying Mg65M25Y10 (M = Cu, Ag, and Ni) metallicglasses in citric acid. Citric acid played a key role due to its capping effect,which reduced the surface diffusion of metals. A structural model consistentwith the sponge-like morphology was constructed to calculate the porosity andthe surface area. The mechanism of the dealloying process in citric acid, involvingligament formation and coarsening, was illustrated. The mechanism was capableof explaining the experimental trends of dealloying, especially the morphology.A glucose sensor, which can be further developed into a high-precision real-timeglucose monitor for medical use, was constructed using sponge-like nanoporouscopper. Our findings are not only relevant to understanding the dealloyingmechanism of metallic glasses, but also provide promising materials for multipleapplications.