Tetracycline and its quantum dots for recognition of Al³⁺ and application in milk developing cells bio-imaging

We developed a technique that detects Al³⁺ in milk/bio-samples, and reversibly applied to recognize tetracycline (TC) in milk, enhancing the fluorescence intensity without interference from other cations (Cd²⁺, Ni²⁺, Co²⁺, Sr²⁺, Mg²⁺, Fe³⁺, K⁺, Sm³⁺, Ag⁺, Na⁺, Ba²⁺, Cr³⁺, Zn²⁺ and Mn²⁺); the limit of detection (LOD) is found to be 0.00022 mM with r² = 0.9439. The detection of Al³⁺ is tested in milk as well as in living cells (Saccharomyces cerevisiae and Debaryomyces spp.) by TC or by its quantum dots. This is consistent with the molecular orbital, revealing that the lowering of the energy of HOMO (Highly Occupied Molecular Orbital) discourages the electron transfer from HOMO of fluorophore to HOMO of excited states of Al-complex that increases the fluorescent intensity. Interestingly, carbon dots (CDs) generated from TC also recognize Al³⁺ as its LOD is as low as to 0.00050 mM with r² of 0.9404.