A Cu2+ fluorescent chemosensor suitable for quantitative detection of tyrosinase in potatoes over a wide pH range.

Cu2+ as an important trace element plays an essential role in various biologic processes due to the unique redox active nature. For this reason, much effort has been made to develop effective methods for Cu2+ detection. In this study, a novel structure fluorescent chemosensor, 1-(6-(((5-(5, 5-difluoro-1, 3, 7, 9-tetramethyl-5H-4λ4, 5λ4-dipyrrolo[1, 2-c:2', 1'-f][1, 3, 2] diazaborinin-10-yl)quinolin-8-yl)oxy)methyl)pyridin-2-yl)-N, N-bis(pyridin-2-ylmethyl)methanamine (1), was synthesized and characterized by 1H and 13C nuclear magnetic resonance spectroscopy, and electrospray ionization mass spectrometry. Sensor 1 showed an obviously "on-off" fluorescence response to Cu2+ with a 1:1 binding stoichiometry by UV-vis and fluorescence spectrophotometry. The detection limit of sensor 1 to Cu2+ was determined to be 1.9 µM, and the stable pH range for Cu2+ detection was from 3 to 13. Sensor 1 can be used for recognition and detection of tyrosinase in potatoes.

A novel fluorescent sensor for specific recognition of GSH based on the copper complex and its bioimaging in living cells.

Given the important role of biothiols in various physiological processes, there is a need to develop novel fluorescent sensors for detecting them. Herein, a novel "on-off-on" fluorescent sensor (E)-N'-((7-(diethylamino)-2-oxo-2H-chromen-3-yl)methylene)-6-((quinolin-8-yloxy)methyl)picolinohydrazide (PQC) was synthesized and its absorbance and fluorescence properties were characterized. The sensor PQC could form a stable complex and showed a significant fluorescence quenching response to Cu2+ with a quenching efficiency of approximately 100%, and the PQC-Cu2+ complex showed a fluorescence enhancement response to GSH with a higher recovery rate of above 80% in a CH3OH/HEPES (9:1 v/v, pH = 7.23) buffer system. Its detection limits were determined to be 0.17 µM for Cu2+ and 0.20 µM for GSH, and the binding stoichiometry of PQC-Cu2+ was determined to be 1: 1 by Job's plot method. Importantly, the sensor PQC can be used for filter paper strip tests and bioimaging in living cells.

A novel fluorescent chemosensor based on coumarin and quinolinyl-benzothiazole for sequential recognition of Cu2+ and PPi and its applicability in live cell imaging.

In this study, a highly selective fluorescent sensor (E)-2-((2-(benzo[d]thiazol-2-yl)quinolin-8-yl)oxy)-N'-((7-(diethylamino)-2-oxo-2H-chromen-3-yl)methylene)acetohydrazide (TQC) was synthesized from 2-methylquinolin-8-ol and 4-(diethylamino)-2-hydroxybenzaldehyde and its structure was characterized by 1H NMR, 13C NMR, ESI-HR-MS and density functional theory (DFT) calculation. Sensor TQC showed an obvious "on-off-on" fluorescence response to Cu2+ and PPi in a DMSO/HEPES (3:2 v/v, pH = 7.4) buffer system. The detection limits of sensor TQC were 0.06 µM to Cu2+ and 0.01 µM to PPi. In addition, sensor TQC showed a 1:1 binding stoichiometry to Cu2+ and TQC-Cu2+ complex showed a 2:1 binding stoichiometry to PPi. The optimum pH range of sensor TQC and TQC-Cu2+ was 3-8. Further studies demonstrated that sensor TQC could be made into test paper strips for the qualitative of Cu2+ and PPi and showed sequentially "on-off-on" fluorescent bio-imaging of Cu2+ and PPi in HeLa cells.

A simple fluorescent probe for detection of Ag+ and Cd2+ and its Cd2+ complex for sequential recognition of S2.

In this study, we designed and synthesized a simple probe 2-(8-((8-methoxyquinolin-2-yl)methoxy)quinolin-2-yl)benzo[d]thiazole (DQT) for detection of Ag+ and Cd2+ in a CH3OH/HEPES (9 : 1 v/v, pH = 7.30) buffer system. Its structure was characterized by NMR, ESI-HR-MS and DFT calculations, and its fluorescence performance was also investigated. Probe DQT showed fluorescence quenching in response to Ag+ and Cd2+ with low detection limits of 0.42 µM and 0.26 µM, respectively. Importantly, the complexation of the probe with Cd2+ resulted in a red shift from blue to green, making it possible to detect Ag+ and Cd2+ by the naked eye under an ultraviolet lamp. The DQT-Cd2+ complex could be used for sequential recognition of S2-. The recovery response could be repeated 3 times by alternate addition of Cd2+ and S2-. A filter paper strip test further demonstrated the potential of probe DQT as a convenient and rapid assay.

A BODIPY-Based Water-Soluble Fluorescent Probe for Naked Eye Detection of pH.

In this study, a BODIPY-based water-soluble fluorescent chemosensor BBP has been synthesized using BODIPY as the fluorescence group and quinoline as the recognition group. BBP can be used for naked eye detection of pH in complete aqueous solution and it shows high specificity in a wide range of cations. The pKa value is determined to be 2.94 and the fluorescence intensity is linearly related to pH in the range of 2.4-3.6.

A chemosensor with a paddle structure based on a BODIPY chromophore for sequential recognition of Cu2+ and HSO3.

In this study, a highly selective chemosensor ML based on a BODIPY fluorescent chromophore was synthesized for sequential recognition of Cu2+ and HSO3 - in a CH3OH/H2O (99 : 1 v/v) system, which contained three recognition sites and its structure characterized by 1H NMR, 13C NMR and ESI-HR-MS. The sensor ML showed an obvious "on-off" fluorescence quenching response toward Cu2+ and the ML-Cu2+ complex showed an "off-on" fluorescence enhancement response toward HSO3 -. The detection limit of the sensor ML was 0.36 µM to Cu2+ and 1.4 µM to HSO3 -. In addition, the sensor ML showed a 1 : 3 binding stoichiometry to Cu2+ and the recovery rate of ML-Cu2+ complex identifying HSO3 - could be over 70%. Sensor ML showed remarkable detection ability in a pH range of 4-8.

A highly sensitive and selective chemosensor for Pb2+ based on quinoline-coumarin.

In this study, a highly sensitive and selective fluorescent chemosensor, ethyl(E)-2-((2-((2-(7-(diethylamino)-2-oxo-2H-chromene-3-carbonyl)hydrazono)methyl)quinolin-8-yl)oxy)acetate (1), was synthesized and characterized by 1H NMR, 13C NMR and ESI-MS. Sensor 1 showed an "on-off" fluorescence response to Pb2+ with a 1 : 1 binding stoichiometry in CH3CN/HEPES buffer medium (9 : 1 v/v). The detection limit of sensor 1 to Pb2+ was determined to be 0.5 µM, and the stable pH range for Pb2+ detection was from 4 to 8.