Preparation of yellow-emitting carbon dots and their bifunctional detection of tetracyclines and Al³⁺ in food and living cells

A novel bifunctional carbon dot (CD)–based sensing platform was constructed for detection of tetracyclines (TCs) and Al³⁺. The fluorescence CDs were fabricated by hydrothermal method using phenylenediamine (p-PD) and ethylenebis(oxyethylenenitrilo) tetraacetic acid (EGTA) as precursors. The obtained prepared CDs show bright yellow fluorescence (y-CDs, E_X = 400 nm and Em = 556 nm), high fluorescence quantum yield (QY = 21.55 ± 0.06%), and preferable optical stability. TCs can directly quench the fluorescence of y-CDs based on static quenching characteristics and a small internal filtration effect (IEF). By adding Al³⁺ to the y-CDs + TCs system, the fluorescence is partly recovered because TCs escape from the surface of the y-CDs and form a more stable chelate with Al³⁺. The sensing platform displays good selectivity and high sensitivity to TCs and Al³⁺ with low detection limits of 0.057–0.23 μM and 0.091 μM, respectively. Importantly, this sensing platform has enabled the detection of TCs and Al³⁺ in milk samples with satisfactory recoveries and RSDs, confirming the reliability and feasibility of this method. Combining with low toxicity and preferable biocompatibility, the y-CDs are extended to cellular imaging and detection of CTC and Al³⁺ in A549 cells. Graphical abstract: