A turn-on red-emitting fluorescent probe for determination of copper(II) ions in food samples and living zebrafish. Zhou Zile,Tang Huihui,Chen Shengyou,Huang Yinghui,Zhu Xiaohua,Li Haitao,Zhang Youyu,Yao Shouzhuo Food chemistry Herein, we developed a turn-on red-emitting fluorescent probe for the sensitive and selective detection of copper ions (Cu) in food samples and living zebrafish. The probe employs a hemicyanine scaffold as the fluorophore and a 2-pyridinecarbonyl group as the recognition receptor and quenching moiety. The 2-pyridinecarbonyl moiety can be specifically cleaved by Cu and results in an approximately 18-fold fluorescence enhancement of the probe, thereby providing a fluorescence turn-on assay for Cu. Additionally, the probe exhibited excellent selectivity, high sensitivity, a broad linear relationship (0.020 to 8.0 μM), and a low limit of detection (4.0 nM, S/N = 3) for Cu. Concomitantly, the probe exhibited satisfactory analytical performance when used with actual food samples. Moreover, the probe could be used for in situ determination of Cu in both living plant tissues and in living zebrafish. 10.1016/j.foodchem.2020.128513