Sandip Mandal

Selective sensing of Hg2+ using rhodamine–thiophene conjugate: Red light emission and visual detection of intracellular Hg2+ at nanomolar level

Rhodamine-thiophene conjugate (L) has been synthesized and characterized by (1)H NMR, FTIR and mass spectra. L shows a large enhancement in emission intensity in presence of Hg(2+). Moreover, naked eye color of L becomes intense red in presence of Hg(2+). The lowest detection limit for Hg(2+) is 1 × 10(-9)M in HEPES buffer (0.1M in EtOH/water, 1/1, v/v, pH 7.4). Hg(2+) induced chelation enhanced fluorescence (CHEF) is associated with spirolacram ring opening of the rhodamine unit. Trace level intracellular Hg(2+) is visualized under fluorescence microscope.

Strategically Modified Rhodamine–Quinoline Conjugate as a CHEF-Assisted FRET Probe for Au3+: DFT and Living Cell Imaging Studies

A systematic journey from O-donor through S-donor to N-donor chelator led to the development of a highly selective Au(3+) chemosensor that operates via a CHEF-induced FRET mechanism. This sensing protocol avoids unwanted possible side reactions observed in alkyne-based gold sensors. DFT studies strongly support the experimental facts. The probe RT-2 detects Au(3+) in the presence of the masking agent KI to minimize Hg(2+) interference; however, RQ-2 selectively detects Au(3+) without any interference and shows reversibility in the sensing in the presence of tetrabutylammonium cyanide. The probe efficiently images Au(3+) in living HeLa cells under a fluorescence microscope.

Zn2+ mediated solvent free solid state red emitting fluorescent complex formation in a mortar–pestle along with living cell imaging studies

An acridone based highly Zn2+ selective, cell-permeable turn-on fluorescence probe (AAS) shows yellow fluorescence at 560 nm (λex, 445 nm) in dry methanol/DMSO up to 100 μM Zn2+. At higher Zn2+ concentration (>100 μM in dry methanol) AAS yields a red solid polymeric complex having strong emission at 605 nm. Interestingly, the red solid polymer also appears at relatively lower Zn2+ concentration (>50 μM) in water. The lowest detection limit of AAS is 0.1 nM Zn2+. AAS is employed for fluorescence bio-imaging of Zn2+ in human MCF 7 breast cancer cells and HeLa cells. Moreover, AAS develops an orange colour detectable by the naked eye in the presence of trace Zn2+ in a mixture of various common cations and anions in the solid state (requires no solvent). Hence, this method is extremely green and interference free. AAS can be employed as a laboratory indicator for detection of Zn2+ in real samples and live cells.

Interaction of water with a benzimidazole derivative: fluorescence and colorimetric recognition of trace level water involving intra-molecular charge transfer process

Benzimidazole‐derived ICT‐based probe, DFPBEN is developed for trace level determination of water. In presence of water, the naked eye color of DFPBEN changes from red to yellow, while it turns to green from red under UV light. Upon addition of water, DFPBEN shows a ratiometric absorbance change in methanol. Copyright

A smart rhodamine-pyridine conjugate for bioimaging of thiocyanate in living cells

A rhodamine–pyridine conjugate, REDA-2PC, can selectively detect NCS− in human embryonic kidney ​293 (HEK293) cells. DFT calculations suggest that this is due to non-covalent interactions (hydrogen bonding N–H⋯NCS−, π–π stacking) and long range electrostatic forces acting between the sulfur atom of the NCS− anion and the NEt2 unit of REDA-2PC. A visible light excitable probe allows fluorescence and naked eye detection of nanomolar NCS−, much lower than normal NCS− levels in the human body. A “lock” and “key” sensing mechanism is established and compared with the corresponding fluorescein derivative as a model compound.

Colorimetric and fluorescence probe for the detection of nano-molar lysine in aqueous medium

A single crystal X-ray structurally characterized BODIPY based probe, THBPY, derived from 4-hydroxy-5-isopropyl-2 methyl-isophthalaldehyde, detects nano-molar lysine in aqueous medium. In the presence of lysine, THBPY visibly changes its color and fluorescence profile due to the formation of a stable imine bond. A distinctive color change allows for facile discrimination over other amino acids in a wide range of concentrations of lysine. The detection limit for lysine is 0.001 μM by a fluorescence method and 0.01 μM by a colorimetric method. The probe shows good reversibility for multiple uses and cleanly discriminates between lysine and other amino acids. Density functional theoretical studies closely resemble experimental results.

Tuning FRET efficiency as a novel approach for improved detection of naphthalene: application to environmental samples.

Naphthalene has emission in the ultraviolet (UV) region, limiting its trace level determination in biological and environmental samples due to detrimental effect of UV light on the living cell and interference from other substances having emission in the UV region. Fluorescence resonance energy transfer strategy is adopted for determination of traces naphthalene in the visible region. Significant improvement of lowest detection limit of naphthalene has been achieved through tuning of fluorescence resonance energy transfer efficiency. Anthranilic acid pyrene (ANP) conjugate provides lowest detection limit for naphthalene among three probes studied, viz. ANB, aniline‐ pyrene conjugate (APA) and ANP. ANP efficiently measures naphthalene content in river water. Copyright