Li et al. 2025 — Ratiometric fluorescent sensor for Al3+ and Cu2+ in food
This methods paper describes the synthesis and validation of a dual-emission ratiometric fluorescent sensor (GQDs@AuNCs) constructed from nitrogen-doped graphene quantum dots (N-GQDs) and glutathione-stabilized gold nanoclusters (G-AuNCs) for simultaneous detection of Al3+ and Cu2+ in food matrices. The sensor was validated by spiked-recovery experiments in fried dough twists, deep-fried dough sticks (Chinese fried bread), scallops, and razor clams (Sinonovacula constricta) purchased in Shenyang, China. The paper does not report ambient (unspiked) Al3+ or Cu2+ concentrations in these food samples; it demonstrates method accuracy via recovery rates.
Key numbers
Detection parameters for Al3+: linear range 0.5–500 µM, LOD 0.66 µM (= approximately 17.8 µg/L or ~17.8 ppb in solution); linear range for Cu2+: 1–200 µM, LOD 0.44 µM (= approximately 28 µg/L in solution). R² = 0.9992 (Al3+), R² = 0.9973 (Cu2+).
Spiked recovery (Al3+) in food matrices: deep-fried dough sticks 99.44%–101.03%; fried dough twists 97.05%–100.48%. Spiked recovery (Cu2+): scallops 96.9%–102.96%; Sinonovacula constricta 90.04%–102.02%. Spiking concentrations: 10 µM, 50 µM, 100 µM.
No endogenous (ambient) Al or Cu concentrations in the food samples are reported. The study does not provide a baseline measurement of Al in the fried dough products; recoveries were calculated from the spiked increment only.
Methods
G-AuNCs synthesised by reducing HAuCl4 with glutathione (GSH) at 80 °C for 24 h. N-GQDs prepared by hydrothermal treatment of graphene oxide (GO) with ammonia at 160 °C. GQDs@AuNCs formed by electrostatic self-assembly. Detection principle: Al3+ produces aggregation-induced emission (AIE) enhancement of G-AuNCs at 528 nm; Cu2+ causes fluorescence quenching of G-AuNCs via charge transfer. N-GQDs emission at 412 nm remains stable as internal reference. Sample preparation: 0.5 g food digested in concentrated HNO3 + 30% H2O2 by microwave (20 min), diluted to 50 mL. Al3+ and Cu2+ standard solutions added at three concentrations. Fluorescence spectrophotometer detection.
Food matrix scope is limited to Chinese fried dough products and shellfish. Selectivity against common interfering ions (Fe3+, K+, Na+, Ca2+, Mn2+, Zn2+, Ba2+, Mg2+) confirmed.
Implications
Certification: This paper provides no ambient Al concentration data usable for contamination profiling. It is a methods-validation study and contributes primarily to understanding of detection technology for Al in high-starch fried foods and shellfish. The fried dough product category is relevant to Al accumulation because alum-based leavening agents (potassium aluminum sulfate, ammonium aluminum sulfate) are used in Chinese fried dough products and are a known source of dietary Al exposure.
Courses: Demonstrates portable fluorescence sensing as an emerging alternative to ICP-OES and AAS for food Al monitoring. Useful for discussion of rapid in-field testing technologies.
App: No ambient concentration data; does not contribute to contamination_profile values.