A Ratiometric Green Fluorescent Carbazole-Bis(hydrazinobenzothiazole) Probe for the Selective Detection of Toxic Hg2+ Ions in Real Water Samples.

A dyad Carbazolyl-bis(hydrazinobenzothiazole) was designed to form a symmetrical structure that containing two-arm active binding sites facilitates coordination with Hg2+ ion. This sensor has imparted a colorimetric and fluorometric changes in presence of Hg2+ ions. The ligand showed a selective blue shift in presence of Hg2+even in co-existence with heavy metal ions with luminescence change from colorless to blue and colorless to green under day light. Enhanced Intramolecular charge transfer process is responsible for fluorescence transformation when ligand interacts with Hg2+ ion. The emission spectra showed a ratiometric response to increasing addition of Hg2+ ions. The sensor is capable of detecting above the lower concentration of 6.8025×10-8 M. The fluorescence efficiency of CBT-2 with Hg2+ ion is quite stable under different co-metal ions and wide range of pH 6 to 9. The sensor CBT-2 forms a 1 : 1 stoichiometric complex with Hg2+ ions and the binding nature is confirmed from the 1H-NMR, FTIR, and mass spectroscopic studies. The sensor CBT-2 and its Hg2+ complex possess good binding nature to protein in Bovine Serum Albumin which could be good in biological applications. Additionally, wedevelop a practical application in real water sample analysis and electrochemical detection via oxidation potential discrimination.

Synthesis of a quinoxaline-hydrazinobenzothiazole based probe-single point detection of Cu2+, Co2+, Ni2+ and Hg2+ ions in real water samples.

A novel quinoxaline-hydrazinobenzothiazole based sensor was synthesized and characterized using NMR, FTIR, and Mass spectroscopy techniques. The sensor achieves the distinct "single-point" colorimetric and fluorescent detection of Cu2+, Co2+, Ni2+ and Hg2+ ions with distinguishable color changes from yellow to red, pale red, pale brown and orange, respectively. The UV-visible and fluorescence emission spectral investigation revealed the excellent single-point sensing ability of the probe towards four different heavy metal ions with a ratiometric response. Nanomolar levels of detection of about 1.16 × 10-7 M, 9.92 × 10-8 M, 8.21 × 10-8 M, and 1.14 × 10-7 M for Cu2+, Co2+, Ni2+ and Hg2+ ions, respectively, were achieved using our sensor, which are below the US-EPA permissible limits. Additionally, the sensor was utilized for naked eye detection under normal daylight. Quantitative determination of the metal ions in real water samples was also demonstrated.

Iminobenzophenone-thiophen hydrazide schiff base: a selective turn on sensor for paramagnetic Fe3+ ion and application in real sample analysis.

A highly selective turn-on sensor for paramagnetic Fe3+ ions based on (E)-N'-((2-aminophenyl)(phenyl)methylene)thiophene-2-carbohydrazide is successfully synthesized. The sensor BPTH is significantly selective and sensitive towards Fe3+ ions over other interfering metal ions especially Cu2+ and Co2+ ions with a lowest limit of recognition 1.48 × 10-7 M. The turn-on sensing mechanism involves enhanced charge transfer. Fe3+ ion forms strong binding with the ligand with a Ka value about 8.23 × 104 M-1 and a 1:1 stoichiometric ratio is confirmed by Job's plot experiment. With Fe3+ ion, the yellow ligand BPTH change to a green fluorescent and reversible with 1 equivalent of EDTA. Practical application of sensor is demonstrated in real sample analysis.

Phenothiazine-Thiophene Hydrazide Dyad: An Efficient "On-Off" Chemosensor for Highly Selective and Sensitive Detection of Hg2+ Ions.

A new phenothiazine-thiophene hydrazone based ((10-ethyl-10H-phenothiazine-3,7-diyl)bis(methanylylidene))bis(thiophene-2-carbohydrazide) (PHT) chemosensor was synthesized via a single-step reaction and utilized as fluorescence "On-Off" sensor towards Hg2+ ion. The PHT was fully characterized by FT-IR, 1H-NMR, and ESI-Mass spectral analysis. The PHT probe was efficiently used for the selective detection of Hg2+ ion in the presence of other metal ions. Further, the stoichiometry of the PHT with Hg2+ complex was confirmed by Job's plot analysis. The limit of detection (LOD) value of the probe PHT was found to be 0.44 × 10-8 M.

Phenothiazine-rhodamine-based colorimetric and fluorogenic 'turn-on' sensor for Zn2+ and bioimaging studies in live cells.

A phenothiazine-rhodamine (PTRH) fluorescent dyad was synthesized and its ability to selectively sense Zn2+ ions in solution and in in vitro cell lines was tested using various techniques. When compared with other competing metal ions, the PTRH probe showed the high selectivity for Zn2+ ions that was supported by electronic and emission spectral analyses. The emission band at 528 nm for the PTRH probe indicated the ring closed form of PTRH, as for Zn2+ ion binding to PTRH, the λem get shift to 608 nm was accompanied by a pale yellow to pink colour (under visible light) and green to pinkish red fluorescence emission (under UV light) due to ring opening of the spirolactam moiety in the PTRH ligand. Spectral overlap of the donor emission band and the absorption band of the ring opened form of the acceptor moiety contributed towards the fluorescence resonance energy transfer ON mechanism for Zn2+ ion detection. The PTRH sensor had the lowest detection limit for Zn2+ , found to be 2.89 × 10-8  M. The sensor also demonstrated good sensing application with minimum toxicity for in vitro analyses using HeLa cells.

A Fluorescent Turn-On Carbazole-Rhodanine Based Sensor for Detection of Ag+ Ions and Application in Ag+ Ions Imaging in Cancer Cells.

Carbazole - Rhodanine conjugate is an effective fluorescent host for silver ions through fluorometric transformation from green to red color with a hyperchromic emission. An intramolecular charge transfer process derived from carbazole towards rhodanine favors interaction of thiocarbonyl S and carboxylic acid O of the rhodanine moiety towards Ag+ ion. Carbazole - rhodanine dyad accomplishes the lowest detection limit of 12.8 × 10-9 M and high quantum efficiency. A fluorescence reversibility of the probe with I- ion surges reutilization of sensor molecule as an Ag+ ion probe with minimal loss in the fluorescent efficiency. This fluorescent ligand is a biocompatible probe and is also a proficient candidate for fluorescent imaging of Ag+ ion in live cells.

Carbazole-azine based fluorescence 'off-on' sensor for selective detection of Cu2+ and its live cell imaging.

A new carbazole-azine based fluorescent sensor was synthesized and characterized. The selectivity of the sensor for Cu2+ over other counter ions in a dimethyl sulfoxide/H2 O mixture was shown through enhancement in fluorescence - an off to on transformation. The specificity of the probe towards Cu2+ was evident in ultraviolet/visible, fluorescence, Fourier transform infrared and mass studies. Application of the probe in the cell imaging and cytotoxicity of living cells is illustrated.

Supramolecular chemical sensors based on pyrene monomer-excimer dual luminescence.

The past ten years have seen a spectacular development of chemical sensors based on the monomer-excimer dual luminescence of aromatic systems, such as pyrene. Either in the form of integrated or multicomponent molecular devices these chemosensors have been attracting a high interest above all because of their unique ratiometric properties. This review will focus on the latter systems, which can be classified into two classes: Firstly, the assembly of receptor-effector conjugates is triggerred by the analyte of interest. As a result, the sensor shows monomer to excimer fluorescence switching upon substrate binding. Secondly, the supramolecular assembly that constitutes the sensor is perturbed by interaction with the analyte. This induces a conformational change or the exchange of a component of the system, which is the cause of the luminescence switch effect.