Magnetic nanosensors for highly sensitive and selective detection of bacillus Calmette-Guérin

With current concerns of the global threat from tuberculosis, it has become important to rapidly identify the bacteria. Traditional technologies involving isolation and amplification of the pathogenic bacteria are complicated and time-consuming. In this work, we describe a sensitive NMR-based detection method to identify bacteria via bacteria-induced self-assembly of magnetic nanoparticles. Bacillus Calmette-Guérin (BCG) was used as a surrogate for Mycobacterium tuberculosis. We prepared the probes by covalent immobilization of the anti-BCG monoclonal antibody onto carboxylic acid-functionalized magnetic nanoparticles. Once a solution containing BCG was introduced, the probes switched from a well dispersed state to an aggregated one, leading to a distinct and dose-dependent change in the spin-spin relaxation time (T2) of the solution. Thus the qualitative and quantitative detection method for BCG was established. The method provides specific detection of as few as 8 bacterial cells per millilitre in experimental samples within 1 hour, which will be promising for rapid detection of M. tuberculosis in clinical samples.     

Triptycene scaffolds: Synthesis and properties of triptycene-derived Schiff base compounds for the selective and sensitive detection of CN− and Cu2+

A series of triptycene-derived Schiff bases were synthesized by condensation between amino triptycenes with an appropriate aldehyde and were isolated in good to excellent (85–90%) yields. Amongst these, a triptycene-hydroxybenzaldehyde Schiff base compound proved to be a selective sensor for cyanide. It exhibited a “turn-on” fluorescence response at 490 nm to CN^? facilitated by the nucleophilic addition of CN^? to the aldehyde group, accompanied by a visible color change from orange to yellow. Likewise, a triptycene salicylaldehyde adduct was shown to be highly sensitive towards the detection of the CN^? ion with a detection limit of 0.9 μM. On the other hand a triptycene-BODIPY Schiff base compound could be used for the detection of Cu²⁺ ions over other competing, biologically relevant metal ions in acetonitrile. Photophysical studies revealed a 1:1 binding model for the triptycene-BODIPY compound.     

On the ‘true position’ of hydrogen in the Periodic Table

Several attempts have recently been made to point to ‘the proper place’ for hydrogen (sometimes also helium) in the Periodic Table of the elements. There are altogether five different types of arguments that lead to the following conclusions: (1) hydrogen should be placed in group 1, above lithium; (2) hydrogen should be placed in group 17, above fluorine; (3) hydrogen is to be placed in group 14, above carbon; (4) hydrogen should be positioned above both lithium and fluorine and (5) hydrogen should be treated as a stand-alone element, in the center of the Periodic Table. Although all proposals are based on arguments, not all of them sound equally convincing. An attempt is made, after critical reexamination of the arguments offered, to hopefully point to the best possible choice for the position of hydrogen. A few words are also mentioned on the structure of the Periodic Table and the (novel) attempts to reorganize it.     

A fluorescence “on–off” sensor for the highly selective and sensitive detection of Cu2+ ion

In an attempt to obtain a model of copper(II) ion-selective sensors, a new 1,8-naphthalimide-based fluorescence chemosensor, N-allylamine-4-[(E)-4-(([2-aminoethyl]imino)methyl) benzene-1,3-diol]-1,8-naphthalimide (NABN), was designed and synthesized. The sensor NABN is fully characterized by melting point analysis, fourier transform infrared spectra, Ultraviolet–visible (UV–vis) spectra, fluorescence spectra, ¹H NMR and ¹³C NMR spectroscopy, and mass spectrometry. NABN showed an unrivaled sensing behavior and an ardent selectivity toward copper(II) ion over other competitive metal ions tested in solution (N,N-Dimethylformamide (DMF)/Tris–HCl buffer, 1:1, v/v, pH = 7.2). The sensor showed a linear fluorescence quenching toward copper(II) ion in the range 0–50 μM, with a detection limit of 1.92 × 10⁻⁷ M estimated. Job's method indicated the formation of a 2:1 coordinative mode of the sensor with copper(II) ion with a high threshold of binding constant of 4 × 10¹² M⁻¹. Combining the above results, the quenching response of NABN toward Cu(II) ions could be ascribed to the strong, intrinsic paramagnetic behavior of Cu(II).     

An improved procedure for the generation and selective trapping of 2,4′-dilithiophenylethyne

2,4′-Dilithiophenylethyne, prepared by treatment of 4-bromophenylethyne with two equivalents of butyllithium, reacts selectively with electrophilic reagents at the 4′-position provided the correct temperature and solvent combination are employed. The successive addition of two different electrophiles gives the 2,4′-dialkylated product in a regioselective manner.     

Development of a sensitive enzyme immunoassay for the detection of phenyl-β-d-thioglucuronide in human urine

Immunoassays for the measurement of glucuronides in human urine can be a helpful tool for the assessment of human exposure to toxic chemicals. Therefore an enzyme immunoassay (EIA) for the specific detection of phenyl-β-d-thioglucuronide was developed. The immunoconjugate was formed by coupling p-aminophenyl-β-d-thioglucuronide to the carrier protein thyroglobulin leaving an exposed glucuronic acid. The hapten-protein conjugate was adsorbed to gold colloids in order to enhance the immunogenic effect. Rabbits were injected with the immunogold conjugates to raise polyclonal antibodies. The resulting competitive assay showed an inhibition by phenyl-β-d-thioglucuronide at sample concentrations of 23.0 ± 1.3 ng/mL (50% B/B₀) and a high cross-reactivity to p-aminophenyl-β-D-thioglucuronide (120%). Little cross-reactivities (< 2%) were observed for potential urinary cross reactants. In addition human urine samples were incubated with β-glucuronidase in order to investigate the EIA for specific matrix effects. An integration of high-performance liquid chromatography (HPLC) and EIA was developed in an attempt to decrease the matrix effects and increase the sensitivity of the overall method. The hyphenated technique HPLC-EIA may be used to monitor human exposure to toxic thiophenol which is excreted by mammals as urinary phenyl thioglucuronide.     

Gold–platinum alloy nanowires as highly sensitive materials for electrochemical detection of hydrogen peroxide

The exploitation of the unique electrical properties of nanowires requires an effective assembly of nanowires as functional materials on a signal transduction platform. This paper describes a new strategy to assemble gold–platinum alloy nanowires on microelectrode devices and demonstrates the sensing characteristics to hydrogen peroxide. The alloy nanowires have been controllably electrodeposited on microelectrodes by applying an alternating current. The composition, morphology and alloying structures of the nanowires were characterized, revealing a single-phase alloy characteristic, highly monodispersed morphology, and controllable bimetallic compositions. The alloy nanowires were shown to exhibit electrocatalytic response characteristics for the detection of hydrogen peroxide, exhibiting a high sensitivity, low detection limit, and fast response time. The nanowire's response mechanism to hydrogen peroxide is also discussed in terms of the synergistic activity of the bimetallic binding sites, which has important implications for a better design of functional nanowires as sensing materials for a wide range of applications.     

A highly sensitive and specific enzyme immunoassay for detection of β-amanitin in biological fluids

Polyclonal antisera to -amanitin were generated in sheep and used to construct a competitive ELISA for measurement of the toxin in human serum and urine. The assay had a detection limit of about 80 pg mL^–1, a dynamic range of 80–2,000 pg mL^–1, a cross reactivity of 22% with -amanitin, and no cross reactivities with cyclic peptides from algal sources. Assay responses in buffer, serum, and urine were remarkably similar. Coupling of the toxin to carrier proteins was carried out by previously unreported methods. The key step that allowed the construction of the highly sensitive assay was the introduction of a novel heterologous hapten derivative made of -amanitin-cyanuric chloride derivative. The new derivative overcame the problems of bridge binding that was, in this case, particularly serious with the homologous hapten derivative. The study demonstrated that the developed antiserum and ELISA procedure can be used to detect -amanitin and related toxins from Amanita phalloides in human serum and urine samples from suspected poison cases and enable early treatment to be administered.     

Highly sensitive and selective DNA-based detection of mercury(II) with α-hemolysin nanopore

The duplex formation mediated by Hg(2+) in a properly designed ssDNA generates a stable hairpin structure, which greatly alters the translocation profile of the ssDNA through α-hemolysin nanopore. From the 2D-events contour plot, the presence of Hg(2+) can be confirmed in as little as 30 min at ～7 nM or higher. The sensor is highly selective to Hg(2+), without interference from other metal ions. It can be fabricated from readily available materials, without the processes of synthesis, purification, probe-making, and so forth. This sensing strategy opens new possibilities for detecting many types of analytes which have specific interactions with DNA molecules.     

Mesoporous silica particles for selective detection of dopamine with β-cyclodextrin as the selective barricade

A mesoporous silica nanoparticle (MSN) based fluorescent sensor for dopamine was constructed with probes inside particle pores and β-cyclodextrin (β-CD) molecules on the particle surface as the selective barricade. The synergistic action of both the hydrophilic rim and hydrophobic cavity of β-CD ensures that the sensor can distinguish dopamine from other biological competitors.     

Smart optical probe for ‘equipment-free’ detection of oxalate in biological fluids and plant-derived food items

A reversible ‘turn-on’ sensor has been designed for ‘naked-eye’ detection of oxalate at nanomolar concentration (～12.5?nM) at pH 7.4. The sensory system shows a highly specific response towards oxalate among a wide range of antinutrients and biologically relevant anionic species. Mechanistic investigations indicate that oxalate can turn the pink-colored solution colorless by dissociating the preformed metal complex. Additionally, high specificity and good accuracy with recovery values ranging from 93.3 to 105.0% were obtained during oxalate estimation in spiked water and human urine samples, confirming the suitability of the present method in estimating trace-level of oxalate in complex matrices. With these results, quantitative estimations of endogenous oxalate were achieved in more than twenty-five different agricultural crops. Finally, low-cost, portable paper strips were developed for on-site detection of oxalate.     

An amphiphilic dendrimer for effective delivery of small interfering RNA and gene silencing in vitro and in vivo

An amphiphilic dendrimer bearing a hydrophobic alkyl chain and hydrophilic poly(amidoamine) dendrons is able to combine the advantageous features of lipid and dendrimer vectors to deliver a heat shock protein?27 siRNA and produce potent gene silencing and anticancer activity in?vitro and in?vivo in a prostate cancer model. This dendrimer can be used alternatively for treating various diseases.     

CdS quantum dots as fluorescence probes for the sensitive and selective detection of highly reactive HSe<Superscript>−</Superscript> ions in aqueous solution

Water-soluble cadmium sulfide (CdS) quantum dots (QDs) capped by mercaptoacetic acid were synthesized by aqueous-phase arrested precipitation, and characterized by transmission electron microscopy, spectrofluorometry, and UV-Vis spectrophotometry. The prepared luminescent water-soluble CdS QDs were evaluated as fluorescence probes for the detection of highly reactive hydrogen selenide ions (HSe⁻ ions). The quenching of the fluorescence emission of CdS QDs with the addition of HSe⁻ ions is due to the elimination of the S²⁻ vacancies which are luminescence centers. Quantitative analysis based on chemical interaction between HSe⁻ ions and the surface of CdS QDs is very simple, easy to develop, and has demonstrated very high sensitivity and selectivity features. The effect of foreign ions (common anions and biologically relevant cations) on the fluorescence of the CdS QDs was examined to evaluate the selectivity. Only Cu²⁺ and S²⁻ ions exhibit significant effects on the fluorescence of CdS QDs. With the developed method, we are able to determine the concentration of HSe⁻ ions in the range from 0.10 to 4.80 μmol L⁻¹, and the limit of detection is 0.087 μmol L⁻¹. The proposed method was successfully applied to monitor the obtained HSe⁻ ions from the reaction of glutathione with selenite. To the best of our knowledge, this is the first report on fluorescence analysis of HSe⁻ ions in aqueous solution. Figure CdS quantum dots as fluorescence probes for the sensitive and selective detection of highly reactive HSe- ions in aqueous solution     

A selective coumarin-based “turn-on” fluorescent sensor for the detection of cysteine and its applications for bioimaging

A coumarin-based compound (1) was designed and synthesized as a new turn-on fluorescent probe for the detection of cysteine. The in vivo imaging of Hi5 cell and Caenorhabditis elegans had further confirmed the cysteine detection by compound 1.     

A novel resorufin based fluorescent “turn-on” probe for the selective detection of hydrazine and application in living cells

In this study, a resorufin derivative RTP-1, which is a novel fluorescent ‘‘turn-on' probe for sensitive detection of hydrazine within 30 min, is designed and synthesized. The selective deprotection of the ester group of the probe by hydrazine led to a prominent enhancement of fluorescent intensity, as well as a remarkable color change from colorless to pink, which could be distinguished by naked eye. The fluorescence enhancement showed decent linear relationship with hydrazine concentration ranging from 0 to 50 mmol/L, with a detection limit of 0.84 mmol/L. The specificity of RTP-1 for hydrazine to a number of metal ions, anions and amines is satisfactory. The sensing mechanism of RTP-1 and hydrazine was evaluated by HPLC, ESI mass spectrometry and density functional theory(DFT).Moreover, we have utilized this fluorescent probe for imaging hydrazine in living cells, and the fluorescence was clearly observed when the cells were incubated with hydrazine(100 mmol/L) for 30 min.     

Rapid and sensitive method for the determination of acetaldehyde in fuel ethanol by high-performance liquid chromatography with UV–Vis detection

A high-performance liquid chromatography (HPLC) method for the determination of acetaldehyde in fuel ethanol was developed. Acetaldehyde was derivatized with 0.900 mL 2,4-dinitrophenylhydrazine (DNPHi) reagent and 50 L phosphoric acid 1 mol L^–1 at a controlled room temperature of 15°C for 20 min. The separation of acetaldehyde-DNPH (ADNPH) was carried out on a Shimadzu Shim-pack C₁₈ column, using methanol/LiCl_(aq) 1.0 mM (80/20, v/v) as a mobile phase under isocratic elution and UV–Vis detection at 365 nm. The standard curve of ADNPH was linear in the range 3–300 mg L^–1 per injection (20 L) and the limit of detection (LOD) for acetaldehyde was 2.03 g L^–1, with a correlation coefficient greater than 0.999 and a precision (relative standard deviation, RSD) of 5.6% (n=5). Recovery studies were performed by fortifying fuel samples with acetaldehyde at various concentrations and the results were in the range 98.7–102%, with a coefficient of variation (CV) from 0.2% to 7.2%. Several fuel samples collected from various gas stations were analyzed and the method was successfully applied to the analysis of acetaldehyde in fuel ethanol samples.     

Trichloroacetonitrile–hydrogen peroxide: a simple and efficient system for the selective oxidation of tertiary and secondary amines

A variety of tertiary and secondary amines were efficiently oxidized to their corresponding N-oxides and nitrones, respectively, using the trichloroacetonitrile–hydrogen peroxide system. The in situ generated trichloromethylperoxyimidic acid is the active reagent for the oxidation processes.     

Transition metal complexes with “non-innocent” ligands in the activation of hydrogen sulfide

The reactions of hydrogen sulfide with transition metal complexes containing redox-active ligands are studied. A combination of electrochemical and spectral data indicates that the one-electron process affording the hydrogen sulfide radical and monoanionic complexes is an elementary act for the most part of the reactions studied. The accessibility of the metal center in the Co, Ni, Zn, and Pt complexes allows hydrogen sulfide to preliminary coordinate to the metal followed by the inner-sphere electron transfer in the hydrogen sulfide-metal-organic ligand system. Active intermediates (radical cation, thiyl radical, and proton) formed due to oxidation react with aromatic substrates. The substitution reaction in the aromatic ring produces a mixture of isomeric thiols and dimerization products of organylthiyl radicals (disulfides).