A homogeneous and “off–on” fluorescence aptamer-based assay for chloramphenicol using vesicle quantum dot-gold colloid composite probes

In this work, a novel homogeneous and signal “off–on” aptamer based fluorescence assay was successfully developed to detect chloramphenicol (CAP) residues in food based on the fluorescence resonance energy transfer (FRET). The vesicle nanotracer was prepared through labeling single stranded DNA binding protein (SSB) on limposome-CdSe/ZnS quantum dot (SSB/L-QD) complexes. It was worth mentioning that the signal tracer (SSB/L-QD) with vesicle shape, which was fabricated being encapsulated with a number of quantum dots and SSB. The nanotracer has excellent signal amplification effects. The vesicle composite probe was formed by combining aptamer labeled nano-gold (Au-Apt) and SSB/L-QD. Which based on SSB's specific affinity towards aptamer. This probe can't emit fluoresce which is in “off” state because the signal from SSB/L-QD as donor can be quenched by the Au-aptas acceptor. When CAP was added in the composite probe solution, the aptamer on the Au-Apt can be preferentially bounded with CAP then release from the composite probe, which can turn the “off” signal of SSB/L-QD tracer into “on” state. The assay indicates excellent linear response to CAP from 0.001 nM to 10 nM and detection limit down to 0.3 pM. The vesicle probes with size of 88 nm have strong signal amplification. Because a larger number of QDs can be labeled inside the double phosphorus lipid membrane. Besides, it was employed to detect CAP residues in the milk samples with results being agreed well with those from ELISA, verifying its accuracy and reliability.     

A novel pyrene-based “off–on” fluorescent probe with high selectivity and sensitivity for Hg2+

In this article, a novel “off–on” fluorescent probe 2-(pyren-1-ylmethylene)-1H-indene-1,3(2H)-dione ( PID ) for Hg²⁺ was designed and synthesized. The selectivity, concentration titration, pH titration, time dependence, limit of detection, and recognition mechanism of PID for Hg²⁺ in CH₃CH₂OH/H₂O solution were also investigated. The results indicated that PID exhibited high selectivity, sensitivity, and fast response to Hg²⁺, and the limit of detection was as low as 20.7 nmol/L. In addition, PID could work in a wide pH range, and the determination of Hg²⁺ in water samples showed that it could be used as a potential detection tool in practical application.     

A biacylhydrazone-based chemosensor for fluorescence ‘turn-on’ detection of Al3+ with high selectivity and sensitivity

A simple Al³⁺ fluorescent chemosensor (1) based on diacylhydrazone has been designed and synthesized by the condensation reaction of 2-hydroxy naphthaldehyde and metaphthalic hydrazide. The chemosensor 1 displays a specific and sensitive response to Al³⁺ over other cations in DMSO solution. Upon the addition of DMSO solution of Al³⁺, the sensor 1 shows an immediate fluorescence ‘turn-on’ response and emitting strong blue emission with visible color change from colorless to green. The fluorescence quantum yield enhanced from 7.24% to 48.68%. Meanwhile, the fluorescence and UV absorption spectra detection limits of the chemosensor 1 for Al³⁺ were 2.0 × 10^?7 M and 5.6 × 10^?7 M respectively, indicating the high sensitivity of 1 to Al³⁺. Furthermore, test strips based on 1 were fabricated, which could be used as a convenient test kit for the detection of Al³⁺ and an efficient Al³⁺ controlled fluorescent security display materials.     

Communication A convenient trifluoroacetylation of amines with trifluoroacetic acid and titanium tetrachloride

In the past years,trifluoroacetylation has been widely used for protecting func-tional groups.For example,trifluoroacetyl can act as an effective blocking group ofhydroxyl and amino substituents in the reactions of a 1-halo-2-hydroxyl-3-amino sugarwith cholesterol or cyclodecanol.Furthermore,the conversion of the basic aminogroup to less basic amido group by trifluoroacetylation provides a good chromatographyseparation method of amines,e.g.cis-,trans-1,2-diaminocyclohexane can be separatedcompletely,via trifluoroacetylation by GLC technique.     

“Getting the best sensitivity from on-capillary fluorescence detection in capillary electrophoresis” – A tutorial

Capillary electrophoresis with Laser-Induced Fluorescence (CE-LIF) detection is being applied to new analytical problems which challenge both the power of CE separation and the sensitivity of LIF detection. On-capillary LIF detection is much more practical than post-capillary detection in a sheath-flow cell. Therefore, commercial CE instruments utilize solely on-capillary CE-LIF detection with a Limit of Detection (LOD) in the nM range, while there are multiple applications of CE-LIF that require pM or lower LODs. This tutorial analyzes all aspects of on-capillary LIF detection in CE in an attempt to identify means for improving LOD of CE-LIF with on-capillary detection. We consider principles of signal enhancement and noise reduction, as well as relevant areas of fluorophore photochemistry and fluorescent microscopy.     

Detection of cyanide (CN−) ion with high selectivity and sensitivity by using ‘Turn-ON’ fluorescence strategy of Rhodamine Schiff base

A Rhodamine based Schiff base, (E)-3′,6′-Bis(ethylamino)-2-(2-(((7-hydroxy-4-methyl-2-oxo-2H-chromen-8-yl)methyl-ene)amino)ethyl)-2′,7′-dimethylspiro[isoindoline-1,9′-xanthen]-3-one (HL) has been synthesized and characterized by various spectroscopic data, viz. ¹H and ¹³C NMR, ESI-MS, FT-IR and elemental analysis. It shows very weak fluorescence emission (9:1 (v/v) DMSO/H₂O, HEPES buffer at pH 7.4) while it is enhanced considerably upon addition of CN⁻ ion selectively (λ_em, 456 ​nm) in presence of nineteen other biologically important anions. The Limit of Detection (LOD) is 24 ​nM which is significantly lower than literature reported data. The binding interaction of the probe to CN⁻ ion, 1:1 (HL:CN⁻) mole ratio has been confirmed by Job's plot, ESI-MS spectral data and ¹H NMR spectral titration measurement.     

An efficient sensor for relay recognition of Zn and Cu through fluorescence ‘off–on–off’ functionality

A new bis(8-carboxamidoquinoline) dangled binaphthol derivatized fluorescent sensor (L) was designed and synthesized. L behaves ratiometric response to Zn²⁺ with high selectivity accompanied by remarkable emission enhancement and red shift. The resultant L–Zn²⁺ complex can act as a Cu²⁺ sensing probe with fluorescence quenching behavior through direct Zn²⁺ ion replacement. Furthermore, the binding modes of Zn²⁺ and Cu²⁺ with L are elucidated by X-ray crystallographic analysis, respectively.     

A new strategy for label-free electrochemical immunoassay based on “gate-effect” of β-cyclodextrin modified electrode

A novel label-free electrochemical immunoassay was developed for prostate-specific antigen (PSA) detection via using β-cyclodextrin (β-CD) assembled layer created gates for the electron transfer of probe. To construct the sensor, a gold electrode was self-assembled with monoclonal anti-PSA antibody labeled 6-mercapto-β-cyclodextrin. Interspaces among β-CD molecules in the layer were automatically formed on gold electrode, which act as the channel of the electron transfer of [Fe(CN)₆]^3−/4− probe. When PSA bind with anti-PSA, it can block these channels on the electrode surface due to their steric hindrance effect, resulting in the decrease in redox current of the probe. Through such a gate-controlled effect, ultra trace amount of PSA may make the currents change greatly after the immunoreaction, which enhanced the signal-to-noise ratio to achieve the amplification effect. By evaluating the logarithm of PSA concentrations, the immunosensor had a good linear response to the current changes with a detection limit of 0.3 pg/mL (S/N = 3) when PSA concentration ranged from 1.0 pg/mL to 1.0 ng/mL. The label-free immunosensor exhibited satisfactory performances in sensitivity, repeatability as well as specificity.     

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).     

A switch-on fluorescence assay for bacterial β-lactamases with amyloid fibrils as fluorescence enhancer and visual tool

Herein is described the development of a novel switch-on fluorescence assay for detecting β-lactamases. The fluorescence assay comprises two components: solid beads coated with a β-lactam antibiotic, which is linked to an environment-sensitive fluorophore (dansylaminothiophenol, DTA), and amyloid fibrils of hen lysozyme (acting as fluorescence enhancer and visual tool). In the presence of the clinically significant TEM-1 β-lactamase, the DTA-antibiotic complex on the solid beads is hydrolyzed, thus releasing the DTA dye into solution. The DTA dye is only weakly fluorescent in solution but gives strong green fluorescence upon binding to lysozyme fibrils. These strongly fluorescent DTA-bound fibrils can be easily visualized by the naked eye upon illumination of the sample with a simple UV lamp. The fluorescence assay can detect TEM-1 at low concentration (0.01 nM). In contrast, no observable fluorescence appears when the fluorescence assay is performed on samples without the TEM-1 β-lactamase.     

Xantphos-ligated palladium dithiolates: An unprecedented and convenient catalyst for the carbonylative Suzuki–Miyaura cross-coupling reaction with high turnover number and turnover frequency

Xantphos- and dithiolate-ligated macrocyclic palladium complexes as an efficient and stable catalyst for the carbonylative Suzuki–Miyaura cross-coupling reaction have been synthesized. The catalysts were characterized by ¹H-nuclear magnetic resonance (NMR), CHNS (carbon, hydrogen, nitrogen, and sulfur) analysis, melting point analysis, and ³¹P-NMR spectroscopy. Several sensitive functional groups (e.g., –NO₂, –F, –Cl, –Br, –NH₂, and –CN) on the aromatic ring were well tolerated in the carbonylative Suzuki–Miyaura coupling reaction. The present palladium complexes produce six times higher turnover number (TON) and five times higher turnover frequency (TOF) compared with conventional homogeneous palladium precursors. Maximum TONs in the range of 10⁵ to 10⁶ and TOF in the range of 10⁴ to 10⁵ could be generated by a very low amount of catalyst loading (10^–5 mol%).     

A selective and sensitive off–on probe for palladium and its application for living cell imaging

A new rhodamine B derivative T1 has been rationally synthesized and displayed selective Pd(Ⅱ)-amplified absorbance and fluorescence emission above 540 nm in methanol–water. Upon the addition of Pd(Ⅱ), the spirolactam ring was unfolded and a 1:1 metal-ligand complex formed, which can be used for ‘‘naked-eyes" detection. In addition, fluorescence imaging experiments of Pd~(2+) in HepG2 living cells showed its valuable application in biological systems.     

A simple and convenient method for direct α-chlorination of ketones with ammonium chloride and Oxone~

When ketones were treated with ammonium chloride and Oxone~ in MeOH at room temperature,a directα-chlorination of ketones was occurred and a series of the corresponding a-chloroketones were obtained in moderate to good yields after 24 h.In this reaction,ammonium chloride was used as the source of chlorine and Oxone~ was used as an oxidant.This method was simple, convenient and providing a novel procedure for preparation of a-chloroketones.     

A off–on pH fluorescence probe derived from phenanthro[9,10-d]imidazol-fluorescein based on ESIPT and ICT

Research on Chemical Intermediates - A novel pH fluorescence probe (PIF), derived from phenanthro[9,10-d]imidazole bound to the fluorescein, is designed and synthesized based on the intramolecular...     

Preparation of carbon supported Pd–P catalyst with high content of element phosphorus and its electrocatalytic performance for formic acid oxidation

The carbon supported Pd–P (Pd–P/C) anodic catalyst in direct formic acid fuel cell (DFAFC) was prepared with a novel phosphorus reduction method. The Pd–P/C catalyst obtained possesses the high content of P⁰ in the alloying state. Because alloying P⁰ could decrease the 3d electron density of Pd and the adsorption affinity of CO and H on Pd, alloying P⁰ would promote the formic acid (FA) oxidation through the direct pathway. Therefore, the electrocatalytic performance of the Pd–P/C catalyst for the FA oxidation is much better than that of the Pd/C catalyst.     

Polyoxometalate-based metal–organic complexes constructed from a new bis-pyrimidine-amide ligand with high capacitance performance and selectivity for the detection of Cr(VI)

In this paper, three new polyoxometalates (POM)-based metal–organic complexes constructed from a new semi-rigid organic ligand N,N'-bis(4-pyrimidinecarboxamido)-1,2-cyclohexane (4-bpmah) H₂[Cu(4-bpmah)₂(SiMo₁₂O₄₀)(H₂O)₂]·2H₂O (1), H[Cu(4-bpmah)₂(PMo₁₂O₄₀)(H₂O)₂]·2H₂O (2) and [Cu(4-bpmah)(H₂O)₂]·[Cu₂(TeMo₆O₂₄)(H₂O)₁₀]·4H₂O (3) were synthesized by hydrothermal method. Single crystal X-ray analyses showed that complexes 1 and 2 were isostructural, in which the isolated Keggin-type [SiMo₁₂O₄₀]^4–/[PMo₁₂O₄₀]^3– anions and [Cu(4-bpmah)₂(H₂O)₂]²ⁿ⁺ units were expanded into 3D supramolecular structures through hydrogen bond interactions. In complex 3, the 1D [Cu(4-bpmah)(H₂O)₂]²ⁿ⁺ metal–organic chains and isolated [Cu₂(TeMo₆O₂₄)(H₂O)₁₀]^2n– units were expanded into a 3D supramolecular framework by the hydrogen bond interactions. In this paper, carbon cloth working electrodes composited by the title complexes (1/CC, 2/CC and 3/CC) were prepared and used as electrodes for supercapacitors. The performance of supercapacitors as well as the influence of electrolyte solution and title complexes quality load on the performance of supercapacitors were studied. Furthermore, the electrochemistry and electrocatalytic behaviors of complexes 1–3 bulk-modified carbon paste electrodes (1-CPE, 2-CPE and 3-CPE) toward the reduction of KBrO₃, KNO₂, Cr(VI), as well as their sensing behaviors on Cr(VI) were investigated.     

A new liquid chromatography–fluorescence method for determination of perfluorooctanesulphonyl fluoride upon derivatisation with 1-naphthol

Perfluorooctanesulphonyl fluoride (PFOSF), as a main precursor of perfluorooctanesulphonate (PFOS) that is ubiquitous in the environment, has been released to the environment with substantial quantity. Determination of PFOSF presents significant analytical challenges for using liquid chromatography with UV (LC–UV) and fluorescence detection (LC–FLD) due to the lack of chromophore in the molecular structure. In this study, a new method was developed by derivatising PFOSF with 1-naphthol to form 1-naphthylperfluorooctanesulphonate (NPFOS), which allowed rapid qualitative and quantitative analysis using LC–UV and LC–FLD. The derivatising product was confirmed from the analyses by proton nuclear magnetic resonance and quadrupole–time of flight mass spectrometry. The LC–FLD method demonstrated good linearity in the NPFOS concentration range from 20 pg µL^?1 to 20 ng µL^?1 with a correlation coefficient better than 0.999, with the instrument detection limit of 1.5 pg µL^?1.