A ratiometric and colorimetric dual-mode fluorescence method for the sensitive determination of copper ion

The present work describes the fabrication of a low-cost, simple, and highly selective analytical method based on the combination of two fluorescent carbon quantum dots (CQDs) for visual or quantitative detection of copper ions at trace levels. Folium cycas and o-phenylenediamine are used as carbon precursors for the preparation of blue fluorescence CQDs (B-CQDs) and yellow fluorescence CQDs (Y-CQDs), respectively. The dual emission ratio fluorescence sensor (B@Y-CQDs), which is obtained through a physical blending method, demonstrates the dual-mode detection of copper ions, including colorimetric detection (visual detection) and ratiometric detection (quantitative detection). Our study reports a portable fluorescent paper sensing platform based on smartphones and computer software that can visually quantify Cu2+ without the need for expensive and bulky laboratory instruments. Upon addition of Cu2+, the simple B@Y-CQDs solution or B@Y-CQDs modified paper-based strip shows a visible color change from blue to yellow under 365 nm ultraviolet light, which achieves visual detection coupled with computer software and smartphones. For the accurate quantitative detection of trace Cu2+, the changes in the fluorescence intensity ratio of F450/550 are recorded, in which B@Y-CQDs exhibited remarkable selectivity and sensitivity, with a low limit of detection (0.73 mu M) within the linear ranges of 7-15 mu M. The applicability of the sensor is explored by the successful detection of Cu2+ in tap water and rice samples. These results provide a novel strategy for the quantitative and visual detection of various metal ions and hold significant potential for applications in food safety assurance and water pollution control.