A dual-emissive carbon dot-functionalized paper-based analytical device for copper ion detection in foods

Abstract

On-site quick analysis of copper (II) ions (Cu^2 +) for food safety assessment requires techniques that are advantageous in terms of reliability, sensitivity, and ease of signal reading. Recognizing the urgent need to develop a portable sensing platform for this purpose, we constructed a fluorescent paper-based analytical device (FPAD) by in-situ synthesis of porphyrin-based dual-emissive carbon dots (DE-CDs). The DE-CDs exhibit two distinct emission peaks at 495 nm and 650 nm, which are attributed to emissions of the carbon core and molecular states, respectively. Upon interaction with Cu²⁺, the emission intensity at 650 nm decreases, while the intensity at 495 nm remains stable, allowing ratiometric fluorescent detection of Cu²⁺ with the single fluorophore-decorated FPAD. The self-calibration effect provided by background emission, in combination with the superior structural stability of FPAD, effectively improves the reliability of Cu²⁺ detection. The efficient electron-withdrawing effect of Cu²⁺ enables FPADs to respond to ultra-trace levels of Cu²⁺, achieving highly sensitive detection (limit of detection: 18.4 nM). Moreover, the obvious emission color transition of FPAD leads to the visualized Cu²⁺ detection and smartphone-based quantification via color analysis. The FPAD effectively excludes interferences from complex food components, setting the basis for Cu²⁺ detection in practical food samples. The spike-recovery rate (86–112 %) is comparable to that of gold-standard methods.