Optical Cu²⁺ probe bearing an 8-hydroxyquinoline subunit: High sensitivity and large fluorescence enhancement

A new fluorescent and colorimetric probe RCu1 with ultra-sensitivity (detection limit is 4.7 nM (3σ)) was developed. It is based on a rhodamine B derivative modified with a functionalized 8-hydroxyquinoline group as a copper-binding site which greatly increases the affinity for Cu²⁺. Cu²⁺ acts not only as a selective recognizing guest but also a hydrolytic promoter. RCu1 showed single-selectively sensing Cu²⁺ over other cations and much larger fluorescence enhancement (as high as over 1000-fold) than those based on Cu²⁺-complexation. The detection mechanism was proved by TOF-MS, FT-IR, ¹H NMR and Gaussian calculations. Based on the outstanding recognition ability of RCu1 toward Cu²⁺, an analytical procedure was developed for Cu ²⁺-determination in natural water samples and soil sample.