Simple silver nanoparticle colorimetric sensing for copper by paper-based devices

► The AgNP colorimetric sensing can be applied for paper-based analytical devices. ► The AgNP modified with homocysteine and dithiothreitol have strong affinity to Cu2+. ► Our method can be used for the determination of Cu2+ in the range of 7.8-62.8 μM within 5 min. ► Our method was successfully applied for the Cu2+ determination in real water samples.