A rapid conductometric sensor for the analysis of cyanide using imidazole based receptor.

A specific and efficient hydrogen bonding interaction between cyanide and the HN-H [imidazole] in an aqueous medium has been utilized for the selective recognition of cyanide under physiological conditions. The possibility of utilizing such an interaction for developing any practical device for the specific detection of cyanide in an aqueous environment has not been explored to date. We now report a simple dip and read conductometric sensor for cyanide ions using a tailored electrode in aqueous media. The purpose built reagent, 2-phenyl-1H-anthra-[2,3-d]-immidazole-5,10 dione was immobilized in a polyaniline matrix to fabricate this conductometric device. The homogeneous immobilization of the receptor in polyaniline was confirmed by FT-IR mapping. The proposed transduction mechanism is charge neutralization on the polyaniline moiety, which ultimately inhibits the protonation resulting in a decrease in the conductance of polyaniline. The sensor response was measured in three ranges of cyanide concentration (10(-10) M to 10(-8) M; 10(-8) M to 10(-6) M and 10(-6) M to 10(-3) M). Whereas the device is found insensitive in the first range, it acts as a detector in the second range and as a proportional sensor in the third range. The minimum detection limit of this device was found to be 10 nmol L(-1) (2.6 ppt), which is significantly less than the WHO guideline values. The responses have been investigated under various conditions such as different pH and the electrochemical state of the polymer. The current device has been found to be better close to neutral pH and at a 400 mV vs. Ag/AgCl potential. The reproducibility and repeatability of the sensor was investigated and interference studies were performed.

Specific Reagent for Cr(III): Imaging Cellular Uptake of Cr(III) in Hct116 Cells and Theoretical Rationalization.

A new rhodamine-based reagent (L1), trapped inside the micellar structure of biologically benign Triton-X 100, could be used for specific recognition of Cr(III) in aqueous buffer medium having physiological pH. This visible light excitable reagent on selective binding to Cr(III) resulted in a strong fluorescence turn-on response with a maximum at ∼583 nm and tail of that luminescence band extended until 650 nm, an optical response that is desired for avoiding the cellular autofluorescence. Interference studies confirm that other metal ions do not interfere with the detection process of Cr(III) in aqueous buffer medium having pH 7.2. To examine the nature of binding of Cr(III) to L1, various spectroscopic studies are performed with the model reagent L2, which tend to support Cr(III)-η(2)-olefin π-interactions involving two olefin bonds in molecular probe L1. Computational studies are also performed with another model reagent LM to examine the possibility of such Cr(III)-η(2)-olefin π-interactions. Presumably, polar functional groups of the model reagent LM upon coordination to the Cr(III) center effectively reduce the formal charge on the metal ion and this is further substantiated by results of the theoretical studies. This assembly is found to be cell membrane permeable and shows insignificant toxicity toward live colon cancer cells (Hct116). Confocal laser scanning microscopic studies further revealed that the reagent L1 could be used as an imaging reagent for detection of cellular uptake of Cr(III) in pure aqueous buffer medium by Hct116 cells. Examples of a specific reagent for paramagnetic Cr(III) with luminescence ON response are scanty in the contemporary literature. This ligand design helped us in achieving the turn on response by utilizing the conversion from spirolactam to an acyclic xanthene form on coordination to Cr(III).

New chemodosimetric probe for the specific detection of Hg2+ in physiological condition and its utilisation for cell imaging studies.

A dithiane derivative of BODIPY is synthesized. This new reagent could be used for the specific and instantaneous detection of Hg(2+) in physiological condition. This dithiane reagent reacts specifically with Hg(2+) to regenerate the parent BODIPY-aldehyde with consequential change in visually detectable optical responses and this provides the possibility of using this reagent as a colorimetric probe or as a fluorescent biomarker/imaging reagent. Further, non-covalent interactions could be utilized for formation of an inclusion complex with biologically benign ß-cyclodextrin for enhancing its solubility in aqueous environment and this included adduct could be used as a fluorescent marker and imaging reagent for Hg(2+). Uptake of Hg(2+) ions in live HeLa cells, exposed to a solution having Hg(2+) ion concentration as low as 2 ppb, could also be detected by confocal laser microscopic studies.

A CN- specific turn-on phosphorescent probe with probable application for enzymatic assay and as an imaging reagent.

A new "turn-on" luminescence probe for imaging the uptake of 0.2 ppm inorganic CN(-) in live HeLa cells as well as for probing the CN(-) generation through an enzymatic process in a virtual aqueous medium at appropriate pH.

Self-assembly of modified rhodamine-6G with tri-block copolymer: unusual vesicle formation, pH sensing and dye release properties.

A new rhodamine-6G derivative having a C18-alkyl chain self-assembles with an amphiphilic tri-block copolymer and forms stable vesicles in water or in water-ethanol (4 : 1, v/v) medium. The stability of the spirolactam form of the rhodamine-6G derivative in these vesicular structures, along with studies of controlled dye release and pH sensing are discussed. Transmission electron micrographs and DLS analyses confirm the formation of vesicular structures. Atomic force microscopy (AFM) images show that the self assembled tri-block copolymer-octadecyl rhodamine vesicles form near spherical nanostructures with a size ranging from 80 to 110 nm. Furthermore, the vesicular system is disassembled under acidic conditions, releasing the cargo which are an integral part of the vesicle. Dye-release studies showed that the release rates of the loaded dye in the vesicles could be well-controlled as a function of the media pH. These results offer an opportunity to use these nanovesicles as imaging reagents for probing media pH with their simultaneous use as nanocarriers for intracellular drug delivery.

An interrupted PET coupled TBET process for the design of a specific receptor for Hg2+ and its intracellular detection in MCF7 cells.

A new coumarin-rhodamine conjugate constitutes a unique example of the interrupted PET coupled TBET response for developing an imaging reagent for determining the intracellular distribution of Hg(2+) in MCF7 cells exposed to [Hg(2+)] as low as 2 ppb.

Ratiometric detection of Cr3+ and Hg2+ by a naphthalimide-rhodamine based fluorescent probe.

Newly synthesized rhodamine derivatives, L(1) and L(2), are found to bind specifically to Hg(2+) or Cr(3+) in presence of large excess of other competing ions with associated changes in their optical and fluorescence spectral behavior. These spectral changes are significant enough in the visible region of the spectrum and thus, allow the visual detection. For L(1), the detection limit is even lower than the permissible [Cr(3+)] or [Hg(2+)] in drinking water as per standard U.S. EPA norms; while the receptor, L2 could be used as a ratiometric sensor for detection of Cr(3+) and Hg(2+) based on the resonance energy transfer (RET) process involving the donor naphthalimide and the acceptor Cr(3+)/Hg(2+)-bound xanthene fragment. Studies reveal that these two reagents could be used for recognition and sensing of Hg(2+)/Cr(3+). Further, confocal laser microscopic studies confirmed that the reagent L(2) could also be used as an imaging probe for detection of uptake of these ions in A431 cells.

Rhodamine-alginate conjugate as self indicating gel beads for efficient detection and scavenging of Hg2+ and Cr3+ in aqueous media.

Effective extraction of Hg(2+) and Cr(3+) ions from aqueous media by novel rhodamine-alginate polymer-based highly fluorogenic, as well as colorimetric, chemosensor beads.

Recognition of Hg2+ and Cr3+ in physiological conditions by a rhodamine derivative and its application as a reagent for cell-imaging studies.

A new rhodamine-based receptor, derivatized with an additional fluorophore (quinoline), was synthesized for selective recognition of Hg(2+) and Cr(3+) in an acetonitrile/HEPES buffer medium of pH 7.3. This reagent could be used as a dual probe and allowed detection of these two ions by monitoring changes in absorption and the fluorescence spectral pattern. In both instances, the extent of the changes was significant enough to allow visual detection. More importantly, the receptor molecule could be used as an imaging reagent for detection of Hg(2+) and Cr(3+) uptake in live human cancer cells (MCF7) using laser confocal microscopic studies. Unlike Hg(ClO(4))(2) or Hg(NO(3))(2) salts, HgCl(2) or HgI(2) failed to induce any visually detectable change in color or fluorescence upon interaction with L(1) under identical experimental conditions. Presumably, the higher covalent nature of Hg(II) in HgCl(2) or HgI(2) accounts for its lower acidity and its inability to open up the spirolactam ring of the reagent L(1). The issue has been addressed on the basis of the single-crystal X-ray structures of L(1)·HgX(2) (X(-) = Cl(-) or I(-)) and results from other spectral studies.

Solvent-dependent aggregation behavior of a new Ru(II)-polypyridyl based metallosurfactant.

Variation of the solvent polarity leads to the formation of vesicles and reverse vesicles of a newly synthesized amphiphilic Ru(II)-polypyridyl complex.

Recognition of Hg(2+) using diametrically disubstituted cyclam unit.

A newly synthesized 1,4,8,11-tetraazacyclotetradecane derivative (L), functionalized with a diazo moiety as the reporter functionality, is found to bind specifically to Hg(2+) with an associated change in color that could be visually detected. With biologically benign ß-CD, it forms an inclusion complex (L·2ß-CD), which shows a much higher solubility in water, and this helps in developing a more intense color on binding to Hg(2+) in a CH(3)CN-HEPES buffer medium. The nontoxic nature of L was checked with the living cells of a Gram negative bacterium, Pseudomonas putida . Further, experiments revealed that these two reagents could be used as staining agents for the detection of Hg(2+) present in this microorganism.

Azine-based receptor for recognition of Hg2+ ion: crystallographic evidence and imaging application in live cells.

A newly synthesized azine-based receptor (L) is found to show remarkable specificity toward the Hg(2+) ion in aqueous media over other metal ions. Coordination of L to Hg(2+) induces a detectable change in color and a turn-on fluorescence response. Restricted C=N isomerization of the azine moieties in the excited state as well as the Photoinduced Electron Transfer (PET) involving the lone pair of electrons of N(1)/N(2) on coordination of L to the Hg(2+) ion account for the turn-on fluorescence response. This reagent could be used for imaging the accumulation of Hg(2+) ions in Epithelial cell line KB 31 cells.

Specific recognition and sensing of CN- in sodium cyanide solution.

Specific recognition of CN(-) in sodium cyanide solution was achieved using two imidazole-based receptors (A and B). Visually detectable color changes were associated with the formation of hydrogen bonded adducts, A.CN(-) and B.CN(-). Ratiometric fluorescence response was achieved for receptor A on binding to CN(-), and this reagent was used for imaging bacterial cells pre-exposed to 1.42 microM CN(-) solution.