The researchers were able to detect copper ions down to 3 ppb with a linearity up to 400 ppb in standard solutions. They also demonstrated the applicability of the paper-based platform in biological matrices, specifically sweat and serum, through recovery studies and by analyzing these biofluids with the paper-based platform and the reference method (atomic absorption spectroscopy), which demonstrated satisfactory accuracy of the novel eco-designed analytical tool. The study highlights filter paper as a unique platform for merging both the fabrication and detection processes. The porous nature of filter paper allows for the preloading of reagents necessary for the development of the assay and accumulation of the target analyte prior to the measurements. The electrochemical analysis of copper ions with a porous platform is often limited by the scarce diffusion of metals within the paper structure to reach the electrode area, affecting sensitivity.