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 Cu(2+). Cu(2+) acts not only as a selective recognizing guest but also a hydrolytic promoter. RCu1 showed single-selectively sensing Cu(2+) over other cations and much larger fluorescence enhancement (as high as over 1000-fold) than those based on Cu(2+)-complexation. The detection mechanism was proved by TOF-MS, FT-IR, (1)H NMR and Gaussian calculations. Based on the outstanding recognition ability of RCu1 toward Cu(2+), an analytical procedure was developed for Cu(2+)-determination in natural water samples and soil sample.