Jahangir Mondal

A ‘chromogenic’ and ‘fluorogenic’ bis-Schiff base sensor for rapid detection of hydrazine both in solution and vapour phases

A novel, convenient and rapid method has been developed, for the first time, for visual detection of hydrazine exploiting a simple, cost-effective Schiff base ligand, L as a fluorescent–colorimetric probe. The sensing behaviour is based on hydrogen bonding recognition. The probe could selectively distinguish hydrazine with an OFF–ON fluorescence signal change and the visible colour change from yellow to colourless at room temperature within 10 seconds. It exhibits exclusive selectivity towards hydrazine over different amines, metal cations and anions. The sensitivity of the fluorescence based assay (0.1 μM or 3.2 ppb) for hydrazine is far below the TLV (threshold limit value) set by the World Health Organization (WHO) and United States Environmental Protection Agency (USEPA). DFT and TDDFT calculations were performed on the molecule of L in order to get the structural information and to get better insight into the sensing mechanism. The probe can be successfully used for vapour-phase discrimination of hydrazine by the TLC plate technique and it shows good practical applicability in the detection of hydrazine in water and urine samples.

A reversible fluorescent-colorimetric chemosensor based on a novel Schiff base for visual detection of CO32− in aqueous solution

A reversible fluorescent colorimetric chemosensor for rapid detection of carbonate ion has been developed based on a novel bis-Schiff base. The chemosensor L employed here is easy to synthesize, eco-friendly and cost effective. It exhibits excellent selectivity and sensitivity towards carbonate ion by changes in both the absorption and fluorescence intensity. The anion recognition occurs indirectly through coordination of a counter metal ion to the Schiff base ligand exhibiting a colour change from colourless to yellow. Microstructural features of L and L + M+ have been investigated by SEM images. The sensitivity of the absorbance based assay (96 nM) for carbonate ion is the lowest ever reported in the literature. The chemosensor L providing rapid response time with sufficiently low detection limit may be useful as a valuable practical sensor for environmental analyses of carbonate ion.

A highly sensitive reversible fluorescent-colorimetric azino bis-Schiff base sensor for rapid detection of Pb2+ in aqueous media

A reversible fluorescent-colorimetric azino bis-Schiff based receptor for the detection of Pb2+ in aqueous medium has been developed for the first time. Receptor L exhibits an excellent selective fluorescent-colorimetric rapid response towards Pb2+. The sensitivity of the fluorescence based assay (8 nM) for Pb2+ is sufficiently low in comparison to that previously reported in the literature. From 1H NMR data, the Job plot measurement and the ESI-MS spectrum, 2 : 1 stoichiometric complexation between L and Pb2+ has been established. Microstructural features of L and L + Pb2+ have been investigated by using SEM images for better understanding the interaction between the chemosensor and Pb2+. Receptor L shows remarkable detection ability in a wide pH range of 4–10 and it has been successfully utilised in the determination of Pb2+ in aqueous solution of bovine serum albumin protein. The geometry of L has been optimized both by DFT calculations and single crystal X-ray studies and that of the Pb2+ complex has been optimized by DFT calculations.

Exploitation of a simple Schiff base as a ratiometric and colorimetric chemosensor for glutamic acid

A novel, exceptionally simple and rapid method has been developed for visual detection of L-glutamic acid (Glu) in aqueous solution. The chemosensor employed is easy to prepare and use with an added advantage of cost effectiveness. It exhibits an excellent selectivity and sensitivity towards Glu over other amino acids by changes in both absorption intensity and colour intensity. The chemosensor provides a fast response time, with an LOD of about 7.96 × 10−7 M suggesting that the chemosensor may be useful as a valuable practical sensor for environmental analyses of glutamic acid.

A new Schiff base and its metal complex as colorimetric and fluorescent‒colorimetric sensors for rapid detection of arginine

A novel Schiff base and its Pb2+-complex have been synthesised and exploited as colorimetric and fluorescent–colorimetric sensors respectively targeting the detection of arginine (Arg). Both the chemo-sensors employed here are simple, easy to synthesize and cost effective. They exhibit excellent selectivity and sensitivity towards Arg by giving dual responsive signals of visible colour change and ‘on–off’ fluorescence change within 1 min. The chemo-sensors having sufficiently low detection limits and rapid response times warrant their application in environmental analyses of Arg.

A fluorescent colorimetric azo dye based chemosensor for detection of S2− in perfect aqueous solution and its application in real sample analysis and building a molecular logic gate

A simple azo-dye based bis-Schiff base chemosensor, L, has been designed, synthesized and characterized by NMR and IR spectroscopy, ESI-MS and elemental analysis. The chemosensor L can successfully detect sulfide ions both visually and spectro-photometrically in perfect aqueous medium as well as in an organic–aqueous mixture through a de-protonation mechanism. The detection limit reaches 16 μM in pure aqueous medium (1.7 μM by UV-vis titration and 3.35 × 10−7 M by fluorescence titration in a 1 : 1 DMSO–H2O mixture), which is the lowest detection limit ever reported in the family of Schiff base chemosensors for sulfide ions. Other interfering anions (F−, Cl−, Br−, HSO3−, N3−, PO43−, NO3−, OAc−, CO32− and CN−) exhibited no interference for the detection of sulfide ions. The mechanism of interaction between L and sulphide ions has further been confirmed by DFT studies. The chemosensor L has also been applied for real sample analysis and in building a molecular logic gate.

A novel pyrene based highly selective reversible fluorescent-colorimetric sensor for the rapid detection of Cu2+ ions: application in bio-imaging

A novel pyrene derivative containing a benzilmonohydrazone moiety has been prepared following a facile synthetic procedure and exploited for the selective detection of Cu2+ under four different channels (colorimetric, absorption, emission and bio-imaging). In the presence of Cu2+, the chemosensor L provided a significant fluorescence enhancement with an easily detectable colour change from yellow to colourless, whereas other metal ions produced only minor changes in colour or fluorescence intensity. The sensitivity of the fluorescence based assay is 7.8 nM for Cu2+, which is far below the limit mentioned in the World Health Organization (WHO) guidelines for drinking water. 1H NMR data, the Job plot and the ESI-MS spectrum prove 1 : 1 stoichiometric complexation between L and Cu2+. The sensing behaviour of the probe has also been well supported by DFT studies. Receptor L exhibits remarkable detection ability in a wide pH range of 4–11 and is successfully utilised in the determination of Cu2+ in real samples. Moreover, L shows its application potential in the detection of Cu2+ in living cells.