Xiaoqing Zhuang

A colorimetric and ratiometric fluorescent probe for thiols and its bioimaging applications

A naphthalimide-based colorimetric fluorescent probe containing a disulfide group was designed and synthesized, which could detect the physiological level of GSH quantitatively by a ratiometric fluorescence method and was successfully applied to the imaging of thiols in living HeLa cells.

Reversible fluorescent probe for highly selective and sensitive detection of mercapto biomolecules.

A coumarin-derived complex, Hg(2)L(2), was reported as a highly sensitive and selective probe for the detection of mercapto biomolecules in aqueous solution. The addition of Cys to a 99% aqueous solution of Hg(2)L(2) resulted in rapid and remarkable fluorescence OFF-ON (emission at 525 nm) due to the ligand-exchange reaction of Cys with L coordinated to Hg(2+). The increased fluorescence can be completely quenched by Hg(2+) and recovered again by the subsequent addition of Cys. Such a fluorescence OFF-ON circle can be repeated at least 10 times by the alterative addition of Cys and Hg(2+) to the solution of Hg(2)L(2), indicating that it can be used as a convertible and reversible probe for the detection of Cys. The interconversion of Hg(2)L(2) and L via the decomplexation/complexation by the modulation of Cys/Hg(2+) was definitely verified from their crystal structures. Other competitive amino acids without a thiol group cannot induce any fluorescence changes, implying that Hg(2)L(2) can selectively determine mercapto biomolecules. Using confocal fluorescence imaging, L/Hg(2)L(2) as a pair of reversible probes can be further applied to track and monitor the self-detoxification process of Hg(2+) ions in SYS5 cells.

Highly selective and sensitive heparin probing from supramolecular assembly of pyrene derivatives.

A new quinine derivative PQ, bearing pyrenyl as a fluorophore, was prepared to recognize heparin in aqueous solution. PQ exhibits good selectivity and sensitivity for heparin over other biological molecules. Upon binding with heparin, PQ shows a typical excimer emission peaked at 489 nm along with a weak monomer emission at 376 nm. Moreover, PQ also shows good performance to detect the heparin in serum.

A novel fluoride ion colorimetric chemosensor based on coumarin

A novel visible colorimetric sensor (L1) with high selectivity for fluoride ion based on coumarin has been synthesized by a simple modification of our earlier report. The chemosensor L1 shows an obvious color change from yellow to blue upon addition of fluoride ion with a large red shift of 145 nm in acetonitrile, and without interference of other anions such as Cl-, Br-, I-, NO3-, H2PO4-, HSO4-, and AcO-. The investigation of 1H NMR spectrum titration indicates the proposed mechanism is that F- first establishes a hydrogen bonding interaction with L1, and then the formation of [F-H-F]- induces deprotonation.

Highly selective recognition of carbenicillin via concerted interactions in 100% aqueous solution

A fluorescent probe (QA) based on quinine bearing two quaternary ammonium groups and a long hydrophobic chain was synthesized, and it showed highly selective recognition of carbenicillin (a typical beta-lactam antibiotic) in 100% aqueous solution via concerted interactions.

Enzyme sensing based on a controllable oxidation reaction

We developed a new method for glutathione reductase (GR) enzyme sensing via a metal-controlled spontaneous oxidation reaction. A new complex HgL, composed of 3-benzothiazoliny-7-N,N-diethylaminocoumarin (L) and HgCl2, was used as an example for illustration. It was found that ligand L was released from complex HgL by a ligand exchange process in the presence of GSH, which was enzymatic reduced from GSSG in the presence of NADH. Subsequently, free ligand L was spontaneously oxidated to a laser dye (coumarin-6) with both fluorescence enhancement and color change. A good linear relationship between fluorescent intensity and GSH concentrations (in the range of 10-40 μM) elicits the potential use of HgL in GSH detection. Based on this result, complex HgL was applied to identify GR from other proteins/enzymes with good selectivity and sensitivity. HgL can also determine GR in the concentration range from 0.5 to 10 U/mL with a linear relationship. Furthermore, this novel sensing method was also expected to be a useful example for the design of other biosensing systems.