Srimanta Manna

Ratiometric fluorescent and chromogenic chemodosimeter for cyanide detection in water and its application in bioimaging

An indole conjugated thiophene–pyridyl (ITP) sensor for cyanide has been synthesized and characterized using NMR and mass spectroscopy. The selectivity of ITP has been explored in aqueous solution, and the resulting ratiometric fluorescence response toward CN−, among 11 different anions, was studied. The complexation of ITP–CN has been addressed using HRMS, 1H-NMR, and UV-vis spectroscopy. ITP displays substantial dual changes in both its ratiometric emission and absorption spectra, exclusively in the presence of CN− in aqueous solution. This is due to the nucleophilic attack of the indolium group of ITP by CN−, which induces a ratiometric fluorescence change and consequently a large emission shift. DFT/TDDFT calculations were performed in order to demonstrate the electronic properties of ITP and the ITP–CN adduct. The resultant ITP–CN adduct was used as a secondary sensing chemo-ensemble for the detection of cyanophilic metal ion-containing molecules by removing CN− from ITP–CN and regenerating ITP with switch-on red fluorescence. For the practical application of the sensor, test strips based on ITP were made up, which could act as suitable and proficient kits for CN− testing and cell studies.

A BODIPY/pyrene-based chemodosimetric fluorescent chemosensor for selective sensing of hydrazine in the gas and aqueous solution state and its imaging in living cells

A BODIPY-based pyrenebutyrate-linked (BPB) chromogenic and fluorogenic probe was synthesized and characterized for the specific detection of hydrazine. In the presence of hydrazine, BODIPY-based pyrenebutyrate was selectively deprotected, producing switch off meso-phenoxyBODIPY along with a color change from yellow to brown, allowing colorimetric detection of hydrazine by the naked eye. Selectivity experiments proved BPB has excellent selectivity to hydrazine over other environmentally abundant ions and common amine-containing species. Probe BPB was also successfully applied in vapor hydrazine detection into a solid state over other interfering volatile analytes. Furthermore, the probe BPB coated with silica gel TLC plates could act as a visual and fluorimetric probe for hydrazine vapor detection. The probe (BPB) has been shown to detect hydrazine up to 1.87 μM at pH 7.4. DFT and TDDFT calculations were performed in order to demonstrate the sensing mechanism and the electronic properties of the probe and hydrazinolysis product. BPB can also be used for the detection of hydrazine in Vero cells without appreciable interference from other biologically abundant analytes.

Highly sensitive ratiometric fluorescence probes for nitric oxide based on dihydropyridine and potentially useful in bioimaging

Hantzsch dihydropyridine-based ratiometric fluorescent NO probes, viz. PyNO and TPANO, were synthesized and characterized. These two probes were shown to be selective and sensitive for NO among the reactive oxygen/nitrogen species (ROS/RNS) studied in HEPES buffer medium by absorption, fluorescence, and visual color change with detection limits of 2.6 μM and 0.08 μM, respectively. Nitric oxide (NO) reacts with Hantzsch dihydropyridines to give the corresponding intensely fluorescent product pyridines via aerobic oxidation and this is applied to detect nitric oxide (NO). A reaction mechanism for dihydropyridine with NO is proposed in this study. The probe shows good stability over a broad pH range (pH > 4). The structures of the PyNO and TPANO probes have been established by single-crystal XRD. DFT and TDDFT calculations were done to demonstrate the electronic properties of the probes and their aromatic products. Moreover, the utility of the PyNO and TPANO probes in detecting NO in live cells has also been demonstrated using Vero cells as monitored by fluorescence imaging. A study of the detection of endogenously generated NO was also carried out by increasing the incubation time of the probe with lipopolysaccharide (LPS) pre-treated cells and it was found that a highly fluorescent cell image could be obtained.

Phenanthroline-fluorescein molecular hybrid as a ratiometric and selective fluorescent chemosensor for Cu2+ via FRET strategy: synthesis, computational studies and in vitro applications

Abstract A FRET-based chemosensor L containing donor phenanthroline and acceptor fluorescein moiety was designed, synthesised and characterised for the ratiometric fluorescent detection of Cu2+ in organo-aqueous solution. Probe L showed high selectivity and excellent sensitivity towards Cu2+ ions by exhibiting both colorimetric and fluorometric changes due to opening of the spirolactum ring of fluorescein upon complexation with Cu2+. In presence of Cu2+ ions, probe L formed L-Cu2+ complex in 1:1 stoichiometric fashion which is established on the basis of Job’s plot and mass spectroscopy. We also performed DFT computational studies to know the binding nature and coordination feature of the complex. Furthermore, fluorescence imaging studies revealed that probe L was cell permeable and could be used to detect intracellular Cu2+ in living cells.

A Michael addition–cyclization-based switch-on fluorescent chemodosimeter for cysteine and its application in live cell imaging

Based on a conjugate addition/intramolecular cyclization sequence, we designed and synthesized a fast response fluorescent probe, BTAC (benzothiazol-azacoumarin), for the discriminative detection of cysteine (Cys). The reaction of cysteine with BTAC results in the cleavage of the acrylate moiety from BTAC, thereby producing BTAC-OH, with a remarkable fluorescence enhancement at 560 nm. The probe exhibits high sensitivity and selectivity toward cysteine over homocysteine and glutathione and the detection limit reached as low as 124 nM for cysteine. The addition of Cys resulted in the color of the solution of BTAC changing from colorless to greenish yellow under the simulation of physiological conditions and BTAC could serve as a “naked-eye” indicator. The structure of BTAC was established by computational DFT (density functional theory) calculation and time dependent density functional theory (TDDFT) calculations were performed to demonstrate the electronic properties of BTAC and its product, BTAC-O−. Finally, the probe was successfully applied for the fluorescence bioimaging of cysteine owing to its photostability and low cytotoxicity.

Reaction-based ratiometric fluorescent probe for selective recognition of sulfide anions with a large Stokes shift through switching on ESIPT

An ESIPT-based, highly selective, ratiometric fluorescent probe BNPT has been synthesized and characterized, which shows turn-on fluorescence response in the presence of S2−, attributed to the removal of a protective 2,4-dinitrobenzene (DNB) moiety, and the resulting fluorescent product has been used for the selective detection of Zn2+. UV-vis and fluorescence spectroscopy analysis, and DFT and TDDFT calculations were carried out to understand the sensing mechanism. The probe BNPT displays a rapid response time and good sensitivity. The probe can detect quantitatively in a concentration range of 0–6.0 μM. The detection limit is 31.3 nM. The sensing ability of BNPT has been successfully applied in real water samples. Applicability as an in-field test kit has been demonstrated by sensing with a BNPT-coated TLC plate. The probe BNPT has been successfully used for visualization of intracellular environment in living cells. The uniqueness lies in the fact that starting with the probe BNPT, sensing can be achieved by two different mechanisms – first, by selective de-protection of the probe BNPT and second, by reacting with the Zn2+ ensemble with S2−.

A benzopyrylium–phenothiazine conjugate of a flavylium derivative as a fluorescent chemosensor for cyanide in aqueous media and its bioimaging

A new benzopyrylium–phenothiazine conjugate (BP) of a flavylium derivative was synthesized and characterized. The probe BP was shown to be selective and sensitive for CN− among the 17 anions and biothiols studied in HEPES buffer medium by fluorescence, absorption, and visual color change. The colorimetric and fluorescence response of the probe BP to cyanide ions is due to the Michael addition of cyanide to the activated Michael receptor of the probe which blocks an intramolecular charge transfer process. The probe displays a fast response to cyanide ions at room temperature, and a maximal fluorescence signal is achieved in the presence of only 2 equivalents of cyanide ions. Moreover, the probe BP could be used as a practical, visible colorimetric test strip for CN− in an aqueous environment. TDDFT calculations were performed in order to demonstrate the electronic properties of the probe and its cyanide product. Density functional reactivity theory (DFRT) calculation also exhibits the characterisation of the most electrophilic and nucleophilic centres of the molecule. The probe could be applied for imaging cyanide in live cells by fluorescence imaging.

A Perylene diimide based fluorescent probe for caffeine in aqueous medium

ABSTRACT Caffeine is a legal stimulant drug which has received considerable attention due to its widespread use as a beverage and in pharmaceutical formulations. However, reported chemosensors for caffeine are limited. In the present study use of a perylene diimide (PDI) derivative has been explored for the first time for detection and quantification of caffeine in an aqueous medium. Spectroscopic studies (UV-Vis, Fluorescence, FTIR and 1H-NMR) suggest that aspartic acid modified perylene diimide (PASP) may bind to caffeine through π-π interaction. This interaction results in immediate quenching of fluorescence and optical color change which can be perceived through naked eyes. This probe has been successfully used for bio-imaging of caffeine in living cells. Graphical Abstract

Installation of efficient quenching groups of a fluorescent probe for the specific detection of cysteine and homocysteine over glutathione in solution and imaging of living cells

Abstract Herein, we report the synthesis and characterisation of a new fluorescent probe 4-(7-nitro-benzo[1,2,5]oxadiazol-4-yl)-benzaldehyde (NBOB) installed with quenching groups for highly selective and sensitive sensing of biothiols. The probe itself is non-fluorescent due to the presence of quenching groups and photoinduced electron transfer (PET) process. Thus, sensitivity of the probe towards thiols was significantly improved by quenching effects. NBOB has been shown to exhibit selective reactivity towards cysteine (Cys) and homocysteine (Hcy) over glutathione (GSH) under stoichiometric conditions. The response mechanism was proved by 1H NMR, LCMS and theoretical calculation. The probe NBOB has been shown to react with Cys present in Vero cells by fluorescence microscopy.