Smart fluorometric sensing of metal contaminants in canned foods: a carbon dot-based dual-response system for quantifying aluminum and cobalt ions

Abstract

The leaching of aluminum and cobalt ions into canned foods, such as aluminum from canned tomato sauce and cobalt from canned tuna, raises concerns about potential health risks, making their accurate detection essential for food safety. In this study, we developed a novel ratiometric fluorometric sensor based on dual-emission carbon dots capable of selectively detecting aluminum (Al³⁺) and cobalt (Co²⁺) ions after a single excitation. The sensor exhibits distinct fluorescence responses: cobalt ions enhance the emission at 403 nm due to interactions with nitrogen and sulfur groups on the carbon dot surface, while Al³⁺ enhance the emission at 532 nm through binding with oxygen-rich groups such as carboxyl and hydroxyl. This differential response stems from the varying affinities of these metal ions for different functional groups, as confirmed through mechanistic studies and comprehensive characterization of the carbon dots, including TEM, UV-Vis, FTIR, and fluorescence lifetime analyses. The method demonstrates excellent sensitivity, with limits of detection (LOD) of 0.012 μM for Co²⁺ and 0.06 μM for Al³⁺. The sensor's performance was validated with real food samples, successfully determining Al³⁺ in canned tomato sauce and Co²⁺ in canned tuna. The method exhibited high selectivity with minimal interference, achieving recovery rates of 97.50-100.67% for Al³⁺ and 97.01-98.02% for Co²⁺. These findings underscore the robustness and practical applicability of the proposed sensor as a reliable tool for monitoring Al³⁺ and Co²⁺ in canned foods, ensuring food safety and compliance with regulatory standards.

Scheme 1. Steps for preparing NSDC-dots.

Fig. 1. (A) TEM image (inset: size distribution histogram), (B) XRD pattern, (C) FTIR spectrum, and (D) XPS spectrum of NSDC-dots.

Fig. 2. XPS spectra of NSDC-dots, showcasing (A) C 1s, (B) N 1s, (C) O 1s, and (D) S 2p regions.

Fig. 3. (A) UV-vis absorption spectra, fluorescence and excitation spectra of NSDC-dots. (B) Fluorescence emission spectra of NSDC-dots after exposing to different excitation wavelengths ranging from 290 to 380 nm.

Fig. 4. (A) Fluorescence spectra of NSDC-dots with Co²⁺ concentration range 0–0.7 μM. The figure inset shows linear relationship between the fluorescence intensity ratio (F₄₀₃/F₅₃₂) and the Co²⁺ concentration. (B) Fluorescence spectra of NSDC-dots with Al³⁺ concentration range 0–1.6 μM. The figure inset shows linear relationship between the fluorescence intensity ratio (F₅₃₂/F₄₀₃) and the Al³⁺ concentration.

Fig. 5. UV-vis absorption spectra of (A) NSDC-dots + Al³⁺, (B) NSDC-dots + Co²⁺, and TEM images of (C) NSDC-dots + Al³⁺, (D) NSDC-dots + Co²⁺.