[en] Highlights: • We demonstrated facile and low-cost fabrication of highly sensitive SERS substrates. • The Ag-Cu substrates display excellent SERS activity with the detection limit of 10⁻¹³ M for Rodamine 6G. • We used combined OR and OA growth mechanisms to describe the formation process of dendritic Ag nanostructures on the Cu substrates. • Our fabrication approach can produce well-defined Ag nanostructures with tailorable optical responses. In this work, we demonstrated facile and low-cost fabrication of highly sensitive SERS substrates via replacement reaction by immersing Cu foils into a AgNO₃ solution. Different morphologies of Ag nanostructures were observed on the substrate surface by controlling the reaction time. The growth mechanism of Ag nanostructures on the Cu substrates was also analyzed based on the nanostructure evolution. The Ag-Cu substrates showed optimum SERS enhancement at certain reaction time, and the minimum detected concentration of Rhodamine 6G is as low as 10⁻¹³ M. The easy and low-cost fabrication makes the Ag-Cu SERS substrates promising for rapid, sensitive detection of targeted analytes, such as biomolecules, pollutants, and explosives in the environment.