A quinoline-based fluorescent chemosensor for palladium ion (Pd2+)-selective detection in aqueous solution.

Quinoline-based fluorescent chemosensors have been extensively developed for various metal cations, but it was still rare for Pd2+-selective detection. In this work, a novel quinoline-benzimidazole conjugate containing one carboxylic acid group (QBM) was designed, and the QBM displayed highly selective fluorescence quenching response towards Pd2+ over other metal cations in aqueous solution. The fluorescence titration revealed a good linear relationship between the fluorescence intensity and the Pd2+ concentration in the range of 0.5-10 µmol L-1, with the detection limit of 0.26 µmol L-1 (S/N = 3). Fluorescence detection of Pd2+ in practical water sample was also successfully achieved.

A selective fluorescent chemosensor for Cd2+ based on 8-hydroxylquinoline-benzothiazole conjugate and imaging application.

A 8-hydroxylquinoline-benzothiazole conjugate (HQ-BT) was facilely synthesized by two steps with >60% total reaction yield. The HQ-BT showed a weak fluorescence that could be strongly enhanced by coordination with various metal ions such as Al3+, Cd2+, Zn2+ in methanol containing 1% water. Interestingly, the selectivity toward Cd2+ was achieved by increasing water fraction to 30% aqueous methanol solution. Thus, the HQ-BT was developed as a new and selective fluorescent chemosensor for Cd2+ in aqueous solution with a broad pH region 4-12. A good linear relationship between the fluorescence intensity and the Cd2+ concentration was found in the range of 0-5 µM with a detection limit of 0.1 µM (S/N = 3). It was also succesfully used for fluorescence imaging of Cd2+ in living cells.

Development of a near-infrared ratiometric fluorescent probe for glutathione using an intramolecular charge transfer signaling mechanism and its bioimaging application in living cells.

A novel near-infrared (NIR) ratiometric fluorescent probe HBT-GSH derived from conjugated benzothiazole was developed for the selective detection of glutathione (GSH) over cysteine (Cys) and homocysteine (Hcy). The probe was sophisticatedly designed based on the GSH selectively induced enhancement of intramolecular charge transfer (ICT) fluorescence. It was synthesized by masking the active phenol group of 2,6-bis(2-vinylbenzothiazolyl)-4-fluorophenol through an acetyl group that acts both as a trigger of the ICT fluorescence and as a recognition moiety for GSH. On its own, the probe HBT-GSH exhibited strong blue fluorescence emission at 426 nm and weak NIR fluorescence emission at 665 nm in aqueous solution, whereas the NIR fluorescence was significantly enhanced and the short emission decreased upon the addition of GSH. Thus an NIR ratiometric fluorescent probe for GSH was developed based on the GSH-selective removal of the acetyl group, therefore switching on the ICT in HBT-GSH. The fluorescence intensity ratio (I665 nm/I426 nm) showed a linear relationship with a GSH concentration of 0-100 µM with a detection limit of 0.35 µM. Moreover, the fluorescent probe was successfully used for the ratiometric fluorescence bioimaging of GSH in living cells.