Krishnendu Aich

Dual channel selective fluorescence detection of Al(III) and PPi in aqueous media with an ‘off–on–off’ switch which mimics molecular logic gates (INHIBIT and EXOR gates)

In this study, we have synthesized a simple Schiff base type isophthaloyl salicylaldehyde hydrazone (ISH) moiety which selectively detects Al(III) and PPi with a fluorescence enhancement at two different wavelengths in aqueous solution. The sensing phenomenon is also reversible and thus the sensor beautifully mimics logic gates (INHIBIT and EXOR gates).

A naphthalimide–quinoline based probe for selective, fluorescence ratiometric sensing of trivalent ions

A new naphthalimide–quinoline based probe (NAQ) is designed and synthesized and its structure is confirmed through single crystal analysis. It detects the trivalent ions (Fe3+ or Al3+ or Cr3+) selectively among other alkali and transition metal ions studied. NAQ shows a distinct ratiometric fluorescence behavior upon addition of trivalent metal ions in CH3CN–HEPES buffer solution (40/60, v/v, pH = 7.4). This fluorogenic sensing of NAQ to M3+ (M3+ = Fe3+ or Al3+ or Cr3+) can be observed by the naked eye, when illuminated under the UV light.

A reaction based colorimetric as well as fluorescence ‘turn on’ probe for the rapid detection of hydrazine

A fluorescein based reactive probe has been designed and synthesized to detect hydrazine selectively over other common analytes. We used here 4-bromobutyrate as a masking unit of fluorescein dye. Hydrazine plays here the role of a de-masking agent to set free the fluorescein dye through a simultaneous substitution–cyclisation–elimination process. This leads to ‘turn on’ fluorescence with easily discernible color change with a fast response time (<15 minutes).

A highly selective and sensitive probe for colorimetric and fluorogenic detection of Cd2+ in aqueous media

A new rhodamine-quinoline based dyad has been synthesized. It shows a highly selective response to Cd(2+) in the presence of other competing metal ions in aqueous media (pH = 7.1). The detection limit of the sensor is in the 10(-7) M level.

Cd2+ Triggered the FRET “ON”: A New Molecular Switch for the Ratiometric Detection of Cd2+ with Live-Cell Imaging and Bound X-ray Structure

On the basis of the Förster resonance energy transfer mechanism between rhodamine and quinoline-benzothiazole conjugated dyad, a new colorimetric as well as fluorescence ratiometric probe was synthesized for the selective detection of Cd(2+). The complex formation of the probe with Cd(2+) was confirmed through Cd(2+)-bound single-crystal structure. Capability of the probe as imaging agent to detect the cellular uptake of Cd(2+) was demonstrated here using living RAW cells.

A Triphenyl Amine‐Based Solvatofluorochromic Dye for the Selective and Ratiometric Sensing of OCl− in Human Blood Cells

A new visible-light-excitable fluorescence ratiometric probe for OCl(-) has been developed based on a triphenylamine-diamiomaleonitrile (TAM) moiety. The structure of the dye was confirmed by single-crystal X-ray analysis. It behaves as a highly selective and sensitive probe for OCl(-) over other analytes with a fast response time (∼100 s). OCl(-) reacts with the probe leading to the formation of the corresponding aldehyde in a mixed-aqueous system. The detection limit of the probe is in the 10(-8) M range. The probe (TAM) also exhibits solvatofluorochromism. Changing the solvent from non-polar to polar, the emission band of TAM largely red-shifted. Moreover, the probe shows an excellent performance in real-life application in detecting OCl(-) in human blood cells. The experimentally observed changes in the structure and electronic properties of the probe after reaction with OCl(-) were studied by DFT and TDDFT computational calculations.

A rhodamine–quinoline based chemodosimeter capable of recognising endogenous OCl− in human blood cells

A rhodamine–quinoline based chemodosimeter (RHQ) has been designed, synthesized and characterized in this paper. The structure of the sensor is confirmed through single crystal X-ray study. It detects hypochlorite (OCl−) selectively among other analytes studied. It showed colorimetric and orange-red fluorescence “turn-on” upon addition of OCl−. The OCl−-promoted ring opening of the rhodamine spirolactam ring in RHQ evokes a large absorbance as well as fluorescence enhancement in water–acetonitrile (1/1, v/v) medium with no significant response to other competitive analytes. Furthermore, we demonstrate here that RHQ can endogenously detect OCl− in human blood cells (peripheral blood mononuclear cells). It also exhibits excellent performance in the “dip stick” method. The optimized structure of the probe is calculated by density functional theory calculations. Moreover, the limit of detection of the probe is in the 10−8 M range.

ESIPT and CHEF based highly sensitive and selective ratiometric sensor for Al3+ with imaging in human blood cells

Based on excited state intramolecular proton transfer (ESIPT) and chelation enhanced fluorescence (CHEF) mechanisms, a new fluorescence ratiometric probe for Al3+ was designed and synthesized, and its structure was confirmed through single crystal X-ray study. This probe is capable of showing excited state intramolecular proton transfer through two different pathways. The introduction of Al3+ in a mixed aqueous solution with the probe results in an abrupt change in the photophysical properties of the probe. A ratiometric emission profile was observed in the presence of Al3+. Interestingly, the presence of other metal ions (especially trivalent ions, e.g. Fe3+, Cr3+, Ga3+ and In3+) do not perturb the fluorescence intensity of the probe (except Cu2+ and Pb2+, where slight changes were noticed). This indicates that the probe shows high affinity towards Al3+. The ratiometric sensing phenomenon may be explained by the presence of two different mechanisms, namely, excited state intramolecular proton transfer and chelation induced enhanced fluorescence, which are demonstrated by the probe in presence of Al3+ in the excited state. The complexation of the probe with Al3+ inhibits excited state intramolecular proton transfer while the chelation induced enhanced fluorescence mechanism becomes dominant. The probe efficiently detected the cellular uptake of Al3+, which is demonstrated here with human blood-cell imaging. Moreover, the detection limit was found to be 6.72 × 10−8 M.

Single sensor for multiple analytes: fluorogenic detection of Al3+ in aqueous media and AcO− in organic media

A simple novel receptor, designed to have a combination of both oxygen and nitrogen-binding sites for metal ion and hydrogen bond donor sites for anion, was synthesised. The receptor has been explored for the selective detection of cation Al3+ over the other interfering metal ions and anion AcO− against a range of physiologically relevant anions in the fluorescence spectroscopy. The receptor shows a different response to aluminium and acetate in the emission spectra. The binding isotherm and detection limit demonstrate that the receptor is an excellent fluorometric probe for Al3+ and AcO− . Our receptor HNQ represents a ‘Single sensor for multiple analytes’. A new array for the ‘naked-eye’ detection of cation (Al3+, blue colour) and anion (AcO− , green colour) in the emission spectra. The dual sensing to Al3+ and AcO− is rare.

Fluorescent chemodosimeter based on spirobenzopyran for organophosphorus nerve agent mimics (DCP)

A new chromogenic as well as fluorogenic protocol based on the spirobenzopyran system for the selective detection of nerve agent mimics (diethyl chlorophosphate or DCP vapour) within a few seconds (∼30 s) is designed, synthesized and characterized in this study. The nucleophilic attack from the oxygen atom of the spiro ring on the electrophilic phosphonyl group of DCP (diethyl chlorophosphate) causes the opening of the spiro (SP) framework and ultimately gives rise to the meta stable merocyanine (MC) form to give a fluorescent species, which gives a signal in the red region (∼675 nm). The ‘turn-on’ red fluorescence and a colorimetric change from colourless to yellow was observed upon the addition of DCP, which evokes almost 124 and 84 fold enhancement in the absorbance and emission intensity, respectively, compare to the probe itself. To the best of our knowledge, such a DCP sensor based on the spirobenzopyran network has not been reported to date. Moreover, the detection limit of this probe was found to be in 10−8 M level in the solution phase. We also developed it as a portable chemosensor kit for DCP and demonstrated its practical application in real-time monitoring.