Subhra Kanti Mukhopadhyay

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.

FRET based tri-color emissive rhodamine–pyrene conjugate as an Al3+ selective colorimetric and fluorescence sensor for living cell imaging

A rhodamine-pyrene hybrid molecule acts as a colorimetric and fluorimetric sensor for Al(3+) through time dependent PET-CHEF and FRET processes associated with tri-color emission. Intracellular Al(3+) has been visualized through time dependent blue-green-red emission. The lowest limit of detection for Al(3+) is 0.02 μM.

Nickel(II)-induced excimer formation of a naphthalene-based fluorescent probe for living cell imaging.

Ni(2+)-induced intramolecular excimer formation of a naphthalene-based novel fluorescent probe, 1-[(naphthalen-3-yl)methylthio]-2-[(naphthalen-6-yl)methylthio]ethane (L), has been investigated for the first time and nicely demonstrated by excitation spectra, a fluorescence lifetime experiment, and (1)H NMR titration. The addition of Ni(2+) to a solution of L (DMSO:water = 1:1, v/v; λ(em) = 345 nm, λ(ex) = 280 nm) quenched its monomer emission, with subsequent enhancement of the excimer intensity (at 430 nm) with an isoemissive point at 381 nm. The fluorescence lifetime of free L (0.3912 ns) is much lower than that of the nickel(2+) complex (1.1329 ns). L could detect Ni(2+) as low as 1 × 10(-6) M with a fairly strong binding constant, 2.0 × 10(4) M(-1). Ni(2+)-contaminated living cells of plant origin could be imaged using a fluorescence microscope.

Recognition of fluoride anions at low ppm level inside living cells and from fluorosis affected tooth and saliva samples

A simple Schiff base chemosensor 2-((2-(2,4-dinitro phenyl)hydrazono)methyl)-4-nitrophenol (L) has been developed as a colorimetric and fluorimetric ‘turn on’ sensor for fluoride (F−). F− recognition at ppm levels from mouth rinses and a toothpaste water solution has been successful. Significantly, L can detect F− from fluorosis affected tooth and saliva samples by similar colorimetric changes. A test kit for F− detection from a DMSO–water (1 : 1) mixture is also engineered. Intracellular F− from pollen grains of Techoma stans and Candida albicans (a diploid fungus), grown in 10−6 (M) F− contaminated water has been successfully detected under a fluorescence microscope.

Interaction of soft donor sites with a hard metal ion: crystallographically characterized blue emitting fluorescent probe for Al(III) with cell staining studies

A naphthalene based compound, 1-((E)-(2-(2-(phenylthio)ethylthio)phenylimino)methyl)naphthalen-2-ol (L2) has been synthesized and characterized by FTIR, 1H NMR, mass spectra and single crystal X-ray structure analysis. L2 shows a blue shift with a large fluorescence enhancement in the presence of Al3+ which is attributed to a chelation-enhanced fluorescence (CHEF) effect with inhibition of an intramolecular charge transfer (ICT) process and cis/trans isomerization. L2 binds to Al3+ with 2 : 1 stoichiometry (mole ratio) with an association constant (Ka) of 0.15 × 104 M−1/2. The detection limit for Al3+ is 5 × 10−8 M in DMSO/H2O (1 : 2, v/v). L2 can efficiently detect intracellular Al3+ under fluorescence microscope

Antipyrine based arsenate selective fluorescent probe for living cell imaging.

Condensation of salicylaldehyde and 4-aminoantipyrine has yielded a new fluorescent probe (APSAL) capable of detecting intracellular arsenate at the micromolar level for the first time. The structure of the probe has been established by different spectroscopic techniques and confirmed from X-ray crystallography. Common anions, viz., F(-), Cl(-), Br(-), I(-), N(3)(-), NCO(-), NO(2)(-), NO(3)(-), SCN(-), CN(-), CH(3)COO(-), SO(4)(2-), ClO(4)(-), and HPO(4)(2-) do not interfere. The binding constant of APSAL for H(2)AsO(4)(-) has been determined using the Benesi-Hildebrand equation as 8.9 × 10(3) M(-1). Fluorescence quantum yield of APSAL (0.016) increases more than 12 times upon binding arsenate ion.

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 simple and dual responsive efficient new Schiff base chemoreceptor for selective sensing of F− and Hg2+: application to bioimaging in living cells and mimicking of molecular logic gates

A novel colorimetric hydrazine-functionalized Schiff base chemoreceptor, NPMP, was synthesized following a simple one-step Schiff base condensation pathway. NPMP showed selective colorimetric change from faint yellow to yellowish orange in the presence of biologically ubiquitous fluoride (F−). It also showed a ‘turn off’ fluorescent response in the presence of F− that could effectively distinguish it from all anions tested except acetate. Acetate (OAc−) caused a weak response, while other anions like chloride, bromide, iodide, phosphate, hydrogen sulfate and nitrate did not have any observable effect on the NPMP receptor (E)-4-nitro-2-((2-(perfluorophenyl)hydrazono)methyl)phenol. Recognition of F− in the presence of NPMP can be explained in light of multiple H-bonding interactions, as well as acid–base interactions between host receptor and guest F−. Interestingly, NPMP also showed enormous potential as a staining agent in determining the presence of low levels of intracellular fluoride. Moreover, it was found that in NPMP⋯F− solutions, incorporation of Hg2+ showed observable optical changes, revealing that this compound is a smart material. Optical responses of NPMP can mimic a molecular logic gate (INHIBIT gate). This can be interpreted as a combination of an AND gate with a NOT function. It also represented a potential ‘Write–Read–Erase–Read’ memory function reflecting multi-writing ability.

A rhodamine–naphthalene conjugate as a FRET based sensor for Cr3+ and Fe3+ with cell staining application

A FRET based fluorescent probe (RDENAPH) containing a 2-hydroxynaphthalene unit as a donor and rhodamine B as an acceptor can discriminate Cr3+ and Fe3+ from other common metal ions through ratiometric sensing. The FRET process has been established from absorption, emission and lifetime decay studies. The probe can stain intracellular Cr3+ and Fe3+ in contaminated living cells.

Triazole-based Zn2+-specific molecular marker for fluorescence bioimaging

Fluorescence bioimaging potential, both in vitro and in vivo, of a yellow emissive triazole-based molecular marker has been investigated and demonstrated. Three different kinds of cells, viz Bacillus thuringiensis, Candida albicans, and Techoma stans pollen grains were used to investigate the intracellular zinc imaging potential of 1 (in vitro studies). Fluorescence imaging of translocation of zinc through the stem of small herb, Peperomia pellucida, having transparent stem proved in vivo bioimaging capability of 1. This approach will enable in screening cell permeability and biostability of a newly developed probe. Similarly, the current method for detection and localization of zinc in Gram seed sprouts could be an easy and potential alternative of the existing analytical methods to investigate the efficiency of various strategies applied for increasing zinc-content in cereal crops. The probe-zinc ensemble has efficiently been applied for detecting phosphate-based biomolecules.