Detection of tetracycline in milk by ratio fluorescence sensor based on non-conjugated polymer dots and Eu³⁺

In order to treat and prevent related bacterial infections, tetracycline(TC)is widely used in animal husbandry and breeding industry due to its broad-spectrum antibacterial activity and low price. Because TC is difficult to be metabolized and its residues in animal derived foods cause harm to human health. Therefore, it is crucial to establish a convenient and fast detection method for TC. In this work, a non-conjugated polymer dots (NCPDs) with good water solubility and high stability blue-green fluorescence were synthesized based on high branched polyethylene imine(PEI) and ascorbic acid (AA). The ratio fluorescence probe for detecting TC content was constructed by simple mixing NCPDs with Eu³⁺and sodium citrate dihydrate. TC can quench the blue-green fluorescence of NCPDs at 490 nm through internal filtering effect, and can also sensitize the red fluorescence of Eu³⁺ at 618 nm through the antenna effect of Eu³⁺. The ratio of fluorescence intensity of 618 and 490 nm has a good linear relationship with the concentration of TC. The method has a rapid fluorescence response with a wider linear range of 50.0 nmol/L to 80.00 μmol/L and a lower limit of detection of 11.8 nmol/L, and the ratiometric fluorescence sensor successfully determined the TC in the milk sample.