An intelligent device with double fluorescent carbon dots based on smartphone for visual and point-of-care testing of Copper(II) in water and food samples

The excessive presence of Cu²⁺ could be harmful to human health. Therefore, a ratiometric fluorescence sensor based on multicolor fluorescent carbon dots (CDs) was developed for Cu²⁺ detection. The blue and yellow carbon dots (B-CDs/Y-CDs) were synthesized by one-step hydrothermal method. After adding Cu²⁺, it is captured by the amino groups of B-CDs to form complexes, resulting in a strong fluorescence quenching via photoinduced electron transfer (PET). Meanwhile, the amino groups from Y-CDs also binds with Cu²⁺ that inhibit the internal PET thus enhancing the fluorescence of Y-CDs. The sensor has the merits in rapid, visual, and selective with a low limit of detection (LOD) at 2.29 nM. Furthermore, an intelligent device composed of portable optical detector and smartphone is constructed, which realizes the visual point-of-care testing (POCT) of Cu²⁺ with a LOD of 7.51 nM. The strategy provides an accessible approach for monitoring heavy metal pollution and food safety.