Bidisha Sarkar

Rhodamine-Based Fluorescent Probe for Al3+ through Time-Dependent PET–CHEF–FRET Processes and Its Cell Staining Application

Rhodamine-diformyl p-cresol conjugate (L) has been developed as a novel Al(3+)-selective fluorometric and colorimetric sensor based on the FRET mechanism for the first time. L can selectively detect Al(3+) through time-dependent PET-CHEF and FRET processes. This phenomenon is nicely reflected from (1)H NMR, fluorescence lifetime, and fluorescence cell imaging studies. The probe can detect Al(3+) as low as 5 × 10(-9) M in HEPES-buffered EtOH:water (0.1 M, 4:1, v/v, pH 7.4). The probe shows pH-dependent emission properties viz. an intense red emission (585 nm) at acidic pH and an intense green fluorescence (535 nm) at basic pH. Thus, L can also be used as a pH sensor via tunable wavelength.

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.

A FRET operated sensor for intracellular pH mapping: strategically improved efficiency on moving from an anthracene to a naphthalene derivative

Two novel fluorescent probes based on anthracene (AAC) and naphthalene (ANC) have been synthesised and characterised. Both the AAC and ANC derivative show green fluorescence at basic pH, but at acidic pH AAC is non-fluorescent, while ANC emits red light. This is attributed primarily to the FRET on–off processes. ANC has better pH discrimination abilities than AAC and can be used to distinguish between different pH environments inside a living cell for the first time.

An INHIBIT logic gate from a thiophene derivative using iron and zinc ions as the input: tuning the efficiency on moving from naphthalene to anthracene to pyrene for the green luminescent detection of the intracellular iron.

A pyrene-thiophene conjugate has been used for the efficient detection of intracellular irons through the generation of bright green luminescence. Amongst three different probes being reported, it is observed that the efficiency for the naked eye green luminescent detection of iron increases on moving from naphthalene to anthracene to pyrene. The developed technique may be very useful to monitor iron and zinc supplementation as single micronutrients in living systems through the construction of an INHIBIT logic gate.

2-(2-Pyridyl) benzimidazole-based ternary Mn(II) complex as an arsenate selective turn-on fluorescence probe: ppb level determination and cell imaging studies

2-(2-Pyridyl) benzimidazole based ternary Mn(II) complex (MnPBINCO) is established as an arsenate selective turn-on fluorescence probe in HEPES buffered (0.1 M, methanol/water = 0.5/99.5, v/v, pH 7.4) solution for the first time. MnPBINCO can determine the presence of HAsO42− at concentrations as low as 1 × 10−10 M and efficiently detect intracellular HAsO42− under a fluorescence microscope.

XRD, HRTEM, Raman and magnetic studies on chemically prepared nanocrystalline Fe-doped gadolinium oxide (Gd1.90Fe0.10O3−δ) annealed in vacuum

Nanoparticles of Fe-doped gadolinium oxide (Gd1.90Fe0.10O3−δ) are prepared by a co-precipitation method. To obtain the desired nanocrystalline phase and to enhance the oxygen vacancy, the as prepared sample is annealed at 700 °C for 6 h in vacuum. The pure crystallographic phase is confirmed by Rietveld analysis of the X-ray diffraction (XRD) pattern. High resolution transmission electron microscopy (HRTEM) studies and Raman spectroscopy of the doped sample observed at room temperature also ruled out the presence of any unwanted impurity phase in the sample. XRD, HRTEM and Raman spectra of the sample confirmed the complete substitution of Fe-ions in the lattice of gadolinium oxide. The static magnetic measurements are carried out at different temperatures from 300 K down to 5 K by using a superconducting quantum interference device (SQUID) magnetometer. The onset of nonlinearity in the magnetization (M) vs. field (H) curve recorded at ∼20 K confirms the presence of magnetic ordering at and below ∼20 K. A clear hysteresis loop with a high value of magnetization (∼120.1 emu g−1) is observed at 5 K at an applied field of ∼5 T. The lack of saturation in the hysteresis loop at and below ∼20 K and good fitting of the M–T curve below ∼50 K by 3D spin wave model and Curie–Weiss law indicates the coexistence of paramagnetic (PM) and ferromagnetic (FM) phases. The observed magnetic phase transition is attributed to the substitution of Fe-ions in the Gd2O3 lattice, which is explained by oxygen vacancy mediated bound magnetic polaron model.

Microstructure investigation, optical properties and magnetic phase transition of Tm3+ substituted nanocrystalline ZnO (Zn0.95Tm0.05O)

The magnetic phase transition, optical and dielectric properties of nanocrystalline Tm3+-doped zinc oxide (Zn0.95Tm0.05O), prepared by the co-precipitation method, were determined for the first time. The oxygen vacancy of the as prepared sample was enhanced by annealing at 200 °C for 6 h in an argon atmosphere. The formation of defects/oxygen vacancy is reflected in the Raman, FTIR and PL spectral analyses of the doped sample. Paramagnetic to ferromagnetic phase transition of Zn0.95Tm0.05O was observed at and below ∼30 K. The onset of ordering is successfully explained by the vacancy assisted bound-magnetic-polaron (BMP) model. The results of dielectric measurements suggest that the dielectric response of Zn0.95Tm0.05O is significantly enhanced, compared to that of pristine ZnO, and this is due to the presence of large amounts of oxygen vacancies, and the nanostructure of the sample.

A visible light excitable pyrene–naphthalene conjugate for ON fluorescence sensing of histidine in living cells

Pyrene appended naphthalene derivative, NEDAP can selectively detect histidine via inter-molecular H-bond assisted molecular ring formation that imparts rigidity to the molecular assembly to inhibit the TICT (Twisted Intra-molecular Charge Transfer) process leading to fluorescence enhancement. 1H NMR titration, mass spectra and DFT (Density Functional Theory) studies nicely demonstrate this sensing process. Visible light excitation favours the living cell imaging as low as 0.01 μM histidine.