Ratiometric fluorescence determination of chlortetracycline based on the aggregation of copper nanoclusters triggered by aluminum ion.

The aggregation-induced emission (AIE) characteristic of copper nanoclusters (CuNC) was for the first time used to construct a ratiometric fluorescence probe (CuNC-Al) for detection of chlortetracycline (CTC). Aluminum ion (Al) can aggregate free CuNC and make it emit a bright and stable red fluorescence. A slight excess of Al in CuNC-Al solution can form a CTC-Al complex to limit the conformational rotation of CTC molecule and enhance CTC fluorescence. So, the red fluorescence of CuNC-Al probe and the enhanced CTC fluorescence are used as a reference signal and a response signal to detect CTC, respectively. The method developed shows a good linear relationship between the CTC concentration and the fluorescence intensity ratio (I/I) in the range 0.1-3.0 µM, and the detection limit is 25.3 nM (S/N = 3). In addition, the fluorescent color of CuNC-Al probe changes from red to yellow-green as the concentration of CTC increases. Based on this observation, a fluorescent test paper has also been fabricated. Schematic illustration of Al inducing CuNC to produce AIE performance and detecting CTC.