Here we report a reusable DNA single-walled carbon nanotube (SWNT)-based fluorescent sensor for highly sensitive and selective detection of Ag+ and cysteine (Cys) in aqueous solution. SWNTs can effectively quench the fluorescence of dye-labeled single-stranded DNA due to their strong pi-pi stacking interactions. However, upon incubation with Ag+, Ag+ can induce stable duplex formation mediated by C-Ag+-C (C = cytosine) coordination chemistry, which has been further confirmed by DNA melting studies. This weakens the interactions between DNA and SWNTs, and thus activates the sensor fluorescence. On the other hand, because Cys is a strong Ag+ binder, it can remove Ag+ from C-Ag+-C base pairs and deactivates the sensor fluorescence by rewrapping the dye-labeled oligonucleotides around the SWNT. In this way, the fluorescence signal-on and signal-off of a DNA/SWNT sensor can be used to detect aqueous Ag+ and Cys, respectively. This sensing platform exhibits high sensitivity and selectivity toward Ag+ and Cys versus other metal ions and the other 19 natural amino acids, with a limit of detection of 1 nM for Ag+ and 9.5 nM for Cys. Based on these results, we have constructed a reusable fluorescent sensor by using the covalent-linked SWNT-DNA conjugates according to the same sensing mechanism. There is no report on the use of SWNT-DNA assays for the detection of Ag+ and Cys. This assay is simple, effective, and reusable, and can in principle be used to detect other metal ions by substituting C-C base pairs with other native or artificial bases that selectively bind to other metal ions.

A reusable DNA single-walled carbon-nanotube-based fluorescent sensor for highly sensitive and selective detection of Ag+ and cysteine in aqueous solutions.

Trace enrichment and determination of silver by immobilized DDTC microcolumn and flow injection atomic absorption spectrometry

Books, Reviews, and Symposia Proceedings 515R Theory and Optimization 516R Theory 516R Optimization 517R Data Analysis 520R Stationary Phase Classification 520R Retention/Solute-Stationary Phase Interactions 521R Modeling/Peak Characterization/Smoothing 521R Calibration and Curve Fitting 521R Deconvolution 521R Factor Analysis 521R Miscellaneous Fundamental Studies 521R Pharmacological and Biological Applications 522R Normal Phase 522R Reversed-Phase 523R Mobile Phase Studies 524R Stationary-Phase Studies 525R Biopolymer Separations 527R Column Packings 527R Reversed Phase 529R Hydrophobic and Hydrophilic Interaction Chromatography 531R

Liquid chromatography: theory and methodology.

Ultra-trace determination of silver in water samples by electrothermal atomic absorption spectrometry after preconcentration with a ligand-less cloud point extraction methodology

Water dispersible SrF2:Tm3+,Yb3+ upconverting nanoparticles (9 nm diameter) have been synthesized to elucidate their potential as ultraviolet emitters. High intensity upconversion ultraviolet emission bands centered at 350 and 360 nm were detected following excitation at 980 nm in the near-infrared region for H2O and D2O colloidal dispersions of the upconverting nanoparticles, corresponding to transitions from the 1I6 and 1D2 energy levels of thulium (Tm3+) ions. Both emission intensities were strongly dependent on the temperature and the H2O/D2O molar ratio of the media, two important criteria that define the different environments in which the nanoparticles can be applied. Since the variations observed were different for each emitting level, the relevance of each band is discussed in relation to these two criteria.

Intense ultraviolet upconversion in water dispersible SrF2:Tm3+,Yb3+ nanoparticles: the effect of the environment on light emissions

The inorganic ion exchanger chromium(III) hexacyanoferrate(III) has been found to be specifically selective for silver ions, with a sorption capacity of ca 10 mequiv g–1 of the exchanger Sorption of the silver ions from acidic (10 mol dm–3 HNO3) and salt solutions (8 mol dm–3 NH4NO3), containing different levels of silver nitrate, has been studied The studies, which were aimed at using the exchanger for the recovery of silver ions from the waste, generated from chemical oxygen demand determinations, showed ca 80–95% recovery of silver ions from concentrated waste The exchanger also selectively removed silver ions from simulated waste containing Bi, Ca, Cd, Co, CuII, Mg, Mn, Ni, Pb and Zn ions

Selective separation of silver from waste solutions on chromium(III) hexacyanoferrate(III) ion exchanger

By measuring the change in potential caused by the addition of sodium citrate to the solutions containing calcium and sodium chlorides, the stability constants (K) of the calcium-citrate(3-) ion pair were determined at ionic strengths 0.02-0.17 mol L −1 and temperatures 18-45°C

Stability constant of the calcium-citrate(3-) ion pair complex

Determination of sulfate in deep subsurface waters by suppressed ion chromatography

A new eluent has been developed for the suppressed ion chromatographic separation of strontium from large amounts of calcium. Together with a Dionex CS-2 separator column, the eluent, a mixture of 2.5 mmol dm–3 ethylenediamine, 5 mmol dm–3 hydrochloric acid and 1 mmol dm–3 Zn2+, was successfully used for the simultaneous determination of strontium, magnesium and calcium in high salinity sub-surface waters. The results of the determination of magnesium, calcium and strontium in sub-surface Arab-D brine and its mixtures with aquifer Wasia and sea-water compare well (p > 0.1) with those obtained by a standard atomic absorption spectrometric method. A base line separation of magnesium, calcium and strontium from each other and from a large excess of sodium in a sub-surface brine can be achieved in approximately 8.0 min. This is a considerably shorter time than that required to achieve a reasonably good separation factor between calcium and strontium by other liquid chromatographic methods, although such methods have not been used for the determination of alkaline earth metal cations in sub-surface waters.

Ethylenediamine–hydrochloric acid–zinc(II) eluent for the suppressed ion chromatographic separation of strontium(II) from a large amount of calcium(II): application of the method to the simultaneous determination of magnesium(II), calcium(II) and strontium(II) in high salinity sub-surface waters

A relatively less expensive Phillips PV 9500/SY 585 automatic energy dispersive X-ray fluorescence (EDXFR) spectrometer with rhodium target, was modified using a commercial kitchen aluminium wrapping foil filter, for the determination of chloride in bifunctional reforming catalysts. Quantitation of chloride was carried out by the Claisse-Quintin method with a catalyst sample of known chloride content as an external standard. The results of EDXRF chloride analysis of different catalyst samples, containing varying amounts of percent carbon and chloride, compared well (p>0.75) with those obtained by silver chloride precipitation method. The small values of percent relative standard deviations at 0.4 to 4.5% showed a good reproducibility of the method. With the total analysis time of a few minutes combined with no sample preparation, the present method seems to be superior as compared to presently employed methods of chloride analysis in reforming catalysts.

Ernesto R. Pambid

Papers

Selective separation of silver from waste solutions on chromium(III) hexacyanoferrate(III) ion exchanger

Stability constant of the calcium-citrate(3-) ion pair complex

Determination of sulfate in deep subsurface waters by suppressed ion chromatography

Ethylenediamine–hydrochloric acid–zinc(II) eluent for the suppressed ion chromatographic separation of strontium(II) from a large amount of calcium(II): application of the method to the simultaneous determination of magnesium(II), calcium(II) and strontium(II) in high salinity sub-surface waters

Energy dispersive X-ray fluorescence analysis of chloride in reforming catalysts