The detection of chemical pollution in an ecosystem requires rapid and accurate analysis in the field. The method presented here can help minimize preparation time and simple detection of the metal ions. Silver nanoparticles are known for their surface plasmon resonance characteristics that visibly display distinctive colors; this makes it possible to develop as colorimetric indicators. In this study, silver nanoparticles were synthesized on paper using velvet apple (Diospyros discolor Willd.) leaf extract as the Ag+ reducing agent. The paper was immersed in the water extract for 1 hour and for 24 hours. The formation of silver nanoparticles was indicated by the change in the paper’s color from white to light brown and dark brown. Furthermore, the paper was tested using several types of metal ions, namely, Cu2+, Mn2+, Pb2+, Zn2+, Mg2+, Ni2+ and Co2+ . For all types of metal ions, the paper’s color changed selectively while detecting Cu2+ ions. The paper-based silver nanoparticles were sensitive enough to detect Cu2+ ions starting at concentrations of 100 mg/L. The Transmission Electron Microscope (TEM) revealed that the silver nanoparticles tended to aggregate after the addition of Cu2+ ions, which caused changes in the size and LSPR of the nanoparticles. This potential method needs further refinement and development to enhance the sensitivity of the paper-based colorimetric indicator, so that it can detect Cu2+ at lower concentrations.