A ratiometric fluorescent sensor for Al³⁺ and Cu²⁺ detection in food samples

Aluminum (Al) and copper (Cu), as two common elements, have specific applications in the modern food industry. However, excessive levels of Al³⁺ and Cu²⁺ pose a major risk to ecosystems and human health. Thus, fast, sensitive, and portable detection technologies are indispensable for achieving source control of such hazardous substances.

We synthesized GSH-stabilized gold nanoclusters (G-AuNCs) and Nitrogen-doped graphene quantum dots (N-GQDs) via a straightforward hydrothermal method, and constructed GQDs@AuNCs ratiometric fluorescent sensors through electrostatic interactions for the rapid detection of Al³⁺ and Cu²⁺ in food samples.

When the concentration of Al³⁺ in the reaction medium increases, the fluorescence intensity (FI) of G-AuNCs incrementally enhances; in contrast, when the concentration of Cu²⁺ increases, the FI of G-AuNCs is gradually quenched. Notably, the FI of N-GQDs remains unchanged throughout this process. When the concentrations of Al³⁺ and Cu²⁺ ions are within the ranges of 0.5-500 μM and 1-200 μM, respectively, the FI ratio (I₅₂₈/I₄₁₂)/(I₅₂₈/I₄₁₂)₀ shows a strong linear correlation with the ion concentrations, with corresponding limits of detection (LOD) of 0.66 μM and 0.44 μM.

The fluorescent sensor features simple synthesis, rapid detection, and high sensitivity, making it well-suited for the rapid detection of Al³⁺ and Cu²⁺ in foods such as fried dough twists and shellfish.