Citrus hystrix peels derived carbon dots based colorimetric and ratiometric fluorescent sensors for highly selective detection of Al3+ in the presence of Zn2+ in water and processed food

Abstract

Carbon dots (CDs), synthesized from Citrus hystrix peels, exhibited maximum fluorescence emission at 420 nm when excited at 330 nm. Along with Quercetin (QT), the CDs quenched the emission at 420 nm upon the addition of aluminium (Al³⁺) ions and the combination also yielded a new strong emission peak at 480 nm. The intensity of the emission peak at 480 nm increased with the increase in Al³⁺ concentration which is accompanied by a visible colour change of the solution from colourless to yellow. The formation of QT-Al³⁺ complex in the system results in the Inner Filter Effect (IFE) causing the change of blue fluorescence emission to green. Herein, a ratiometric fluorescent sensor has been constructed using CD-QT system which exhibits a great potential towards selective determination of Al³⁺ by overcoming the limitations possessed by single wavelength detection probes. The proposed sensor detects Al³⁺ over a wide range of 5–550 µM with the lowest detection limit of 0.695 µM. Also, this sensor hardly shows any vulnerability towards the most possible interfering Zinc ions and other potential metal ions. The proposed method has been successfully applied for the determination of Al³⁺ leached from aluminium food wrapper and cooking utensil with high selectivity. Excessive leaching of Al³⁺ into food has been evidenced while cooking in acidic conditions using this sensor. The fabricated fluorescent sensor has been used to detect Al³⁺ in sediments collected from large scale wheat storage warehouses, where aluminium phosphide is used as fumigant for pest control.