Copper, as the third most abundant transition metal ions of human, plays an essential role in the redox reaction, signal transduction, hematopoiesis, and other physiological processes. Abnormal content of copper ions in the body will cause some diseases such as anemia, coronary heart disease, Menkes’ syndrome. In this article, a new fluorescence probe L for Cu²⁺ was designed and synthetized by using 4-bromo-1,8 naphthalene anhydride and 2-thiophene formaldehyde as raw materials. Fluorescent probe L itself exhibited strong fluorescence, upon the addition of Cu²⁺ ions, the fluorescence was quenched. The fluorescent detection limit for Cu²⁺ ions was determined to be 1.8 μM based on a 3δ/S method. UV-vis absorption and fluorescence spectra indicated that probe L showed good selectivity and sensitivity for Cu²⁺, and this selectivity was not interfered by other metal ions and anions. Further cell fluorescence imaging experiments indicated that the probe L had potential to be used to examine copper ions in vivo.

A fluorescence chemosensor, 2-hydroxy-1-naphthaldehyde azine (HNA) was designed and synthesized for sequential detection of Cu²⁺ and biothiols. It was found that HNA can specifically bind to Cu²⁺ with 1:1 stoichiometry, accompanied with a dramatic fluorescence quenching and a remarkable bathochromic-shift of the absorbance peak in HEPES buffer. The generated HNA-Cu²⁺ ensemble displayed a “turn-on” fluorescent response specific for biothiols (Hcy, Cys and GSH) based on the displacement approach, giving a remarkable recovery of fluorescence and UV-Vis spectra. The detection limits of HNA-Cu²⁺ to Hcy, Cys and GSH were estimated to be 1.5 μM, 1.0 μM and 0.8 μM, respectively, suggesting that HNA-Cu²⁺ is sensitive enough for the determination of thiols in biological systems. The biocompatibility of HNA towards A549 human lung carcinoma cell, was evaluated by an MTT assay. The capability of HNA-Cu²⁺ to detect biothiols in live A549 cells was then demonstrated by a microscopy fluorescence imaging assay.

A coumarin–Cu²⁺ ensemble based fluorescent chemosensor was developed for the selective detection of cysteine in aqueous media and live cells.