Multicolor fluorescence assay of tetracycline: lanthanide complexed amino clay loaded with copper nanoclusters

A multicolor fluorescent nanoprobe has been prepared by loading bovine serum albumin-stabilized copper nanoclusters (BSA-Cu NCs) onto amino clay (AC) and grafting Eu³⁺ with auxiliary ligand citric acid (Cit). Tetracycline (TC) can coordinate with Eu³⁺ by β-diketone structure and transfer energy to Eu³⁺ through antenna effect. When the concentration of TC is in the range 0 to 13 μM, the blue emission intensity of BSA-CuNCs is basically unchanged, and the red emission of Eu³⁺ is remarkably enhanced due to the coordination with TC. The emission color gradually changes from blue to red under UV lamp (λ = 365 nm). However, when the TC concentration is in the range 13 to 350 μΜ, the internal amino acid residues of BSA sensitize TC, and the emission color gradually changed from red to green. The nanoprobe has rich color, is simple to prepare, portable, and provide a wide detection range. The limit of detection (LOD) is 3.04 nM, which could be used for real-time visual analysis of trace TC in actual samples (lake water, milk, honey, and bovine serum albumin). In addition, a visual test paper has been designed and combined with the color scanning APP of a smartphone to complete the qualitative and semi-quantitative test of TC. BSA-Cu NCs were loaded on amino clay and graft Eu³⁺ to establish ratiometric fluorescent nanoprobe for TC detection. With the increase of TC concentration, the emission color under 365 nm UV lamp gradually changed from blue to red and then to green, and the color changed obviously and can be observed by the naked eye. The visual test paper and smartphone application detection sensor were developed to realize rapid, convenient, real-time, and visual detection of TC in actual samples.