Polypyrrole deposited on the core-shell structured nitrogen-doped porous carbon@Ag-MOF for signal amplification detection of chloride ions.

An electrochemical platform for signal amplification probing chloride ions (Cl-) is constructed by the composite integrating core-shell structured nitrogen-doped porous carbon@Ag-based metal-organic frameworks (NC@Ag-MOF) with polypyrrole (PPy). It is based on the signal of solid-state AgCl derived from Ag-MOF, since both NC and PPy have good electrical conductivity and promote the electron transport capacity of solid-state AgCl. NC@Ag-MOF was firstly synthesized with NC as the scaffold and then, PPy was anchored on NC@Ag-MOF by chemical polymerization. The composite NC@Ag-MOF-PPy was utilized to modify the electrode, which exhibited a higher peak current and lower peak potential during Ag oxidation compared with those of Ag-MOF and NC@Ag-MOF-modified electrodes. More importantly, in the coexistence of chloride (Cl-) ions in solution, the NC@Ag-MOF-PPy-modified electrode displayed a fairly stable and sharp peak of solid-state AgCl with the peak potentials gradually approaching zero, which might effectively overcome the background interference caused by electroactive substances. The oxidation peak currents of solid-state AgCl increased linearly with the concentration of  Cl- ions in a broad range of 0.15 µM-40 mM and 40-250 mM, with detection limits of 0.10 µM and 40 mM, respectively. The practical applicability for Cl- ions determination was demonstrated using human serum and urine samples. The results suggest that NC@Ag-MOF-PPy composite could be a promising candidate for the construction of the electrochemical sensor.

Water-soluble non-conjugated polymer dots with strong green fluorescence for sensitive detection of organophosphate pesticides.

Water-soluble non-conjugated polymer dots (PDs) have been synthesized using hyperbranched polyethyleneimine (PEI) and dihydroxybenzaldehyde (DHB) for the first time via the Schiff base reaction at room temperature. The yielded non-conjugated PDs of PEI-DHB could display the well-defined spheric structure and good water solubility. In contrast to the common PDs otherwise showing blue emission, the PEI-DHB PDs could give out strong green fluorescence in aqueous media. Especially, the fluorescence of the PEI-DHB PDs could be specifically quenched by MnO2 nanosheets through the inner filter effects and further restored by the thiocholine that could reduce MnO2 nanosheets into Mn2+. Herein, thiocholine could be produced in hydrolysis reaction of acetylthiocholine catalyzed by the acetylcholinesterase (AChE), of which the catalytic activity could be irreversibly inhibitted by the introduction of organophosphates. A highly selective fluorimetric method was thereby been developed for the detection of organophosphorus pesticides using dimethyl-dichloro-vinyl phosphate as a model. The linear concentrations ranges from 0.050 to 2.5 µM. Importantly, the non-conjugated PDs probes with strong green fluorescence and high water solubility may promise the extensive applications in the environmental, food, and clinical analysis fields.

A magnet-renewable electroanalysis strategy for hydrogen sulfide in aquaculture freshwater using magnetic silver metal-organic frameworks.

A magnet-renewable electroanalytical strategy has been initially developed for monitoring hydrogen sulfide (H2S) in aquaculture freshwater systems using magnetic Fe3O4-loaded silver metal-organic framework (Fe3O4@Ag-MOF). The magnetic composites were synthesized by a hydrothermal route and further attached onto the magnetic electrodes. It was discovered that the Fe3O4@Ag-MOF-based electrochemical sensors could exhibit the extremely sharp and steady signals of solid-state Ag/AgCl electrochemistry at a lower potential. Furthermore, the highly specific and irreversible S-Cl replacement reactions could occur in the presence of H2S, so as to induce the conversion of AgCl into non-electroactive Ag2S with the rational decline of Ag/AgCl signals. Importantly, the Fe3O4@Ag-MOF-modified electrodes could be renewed simply by the removal of the magnet after each of the detection cycles for the next immobilization of Fe3O4@Ag-MOF probes. The developed electroanalytical method could facilitate the detection of H2S in the linear range from 4.0 to 1400 nM, with a limit of detection down to 2.0 nM. Besides, it was employed to detect H2S in aquaculture freshwater samples of fish, crab, and shrimp, showing the satisfactory results.

A highly selective and recyclable sensor for the electroanalysis of phosphothioate pesticides using silver-doped ZnO nanorods arrays.

Silver-doped ZnO nanorods (Ag/ZnO) arrays have in-situ grown onto indium tin oxide (ITO) via the one-pot hydrothermal route towards a highly selective and recyclable electroanalysis of phosphothioate pesticides (PTs) with phoxim (Phox) as a model. It was discovered that the Ag/ZnO arrays-modified electrode could obtain a steady and sharp electrochemical output of solid-state Ag/AgCl at a low potential (i.e., 0.12 V). More importantly, the achieved Ag/AgCl signals could decrease selectively induced by sulfide (S)-containing Phox by the specific Cl-S displacement reaction, which would trigger AgCl into non-electroactive Ag-Phox complex. The Ag/ZnO arrays-modified sensors present a linear range from 0.050 to 700.0 µM for the detection of Phox, with a limit of detection down to 0.010 µM. The practical applicability of the developed electroanalysis strategy was successfully employed to detect Phox in the tap water and cabbage samples. Moreover, the photocatalytic performances of the Ag/ZnO arrays were subsequently verified for the degradation of Phox, displaying the higher photocatalytic efficiency than pure ZnO nanorods. Besides, the as-developed sensor can allow for the recyclable detection of Phox by the Ag/ZnO-photocatalyzed removal of Phox after each of the detection cycles. Therefore, the sensors platform based on Ag/ZnO arrays can be expected to have potential for the electrochemical monitoring and photocatalytic degradation of toxic pesticides in the food and environmental fields.

Coating silver metal-organic frameworks onto nitrogen-doped porous carbons for the electrochemical sensing of cysteine.

Nitrogen-doped porous carbons (N-PC) were coated for the first time with silver metal-organic frameworks (Ag-MOF) by the hydrothermal route. The resulted N-PC@Ag-MOF composites present high stability because of the strong interaction between N atoms of N-PC and Ag+ ions of Ag-MOF. It was discovered that the electrodes modified with N-PC@Ag-MOF composites display much higher conductivity than the one modified with Ag-MOF. Especially, they provide stable and sharp electrochemical signals of solid-state AgBr at a low potential approaching zero (i.e., 0.02 V), which may aid to overcome the drawback of the traditional electroanalysis at high overpotentials with serious interferences from the samples background. More importantly, the yielded AgBr signals selectively decrease induced by cysteine (Cys) through the specific thiol-bromine replacement reactions that transfer AgBr into non-electroactive Ag-Cys. The proposed method facilitates the selective detection of Cys with two linear working ranges of 0.10 to 100 µM and 100 to 1300 µM, respectively. The N-PC@Ag-MOF-based sensors have been used for detection of spiked Cys in milk samples with good recovery efficiencies. The developed electroanalysis strategy for probing Cys through the specific thiol-bromine replacement has potential applications in the food analysis fields. Ag-MOF was coated onto heteroatoms co-doped porous carbons carriers for the selective electroanalysis strategy for cysteine at the potential approaching zero using Br- ions.

Electrochemical sensor for detection of hydrogen peroxide modified with prussian blue electrodeposition on nitrogen, phosphorus and sulfur co-doped porous carbons-chitosan.

Nitrogen, phosphorus and sulfur co-doped porous carbons (N, P, S@PC) were well dispersed in the chitosan (CS) acid solution, in particular via covalently interaction, which could avoid the aggregation of N, P, S@PC in most solvents. Moreover, CS could also avoid N, P, S@PC leakage from the modified electrode. A novel electrochemical sensor was then developed through prussian blue (PB) was electrodeposited on the glass carbon (GC) electrode modified with N, P, S@PC-CS composite. Results with scanning electron microscopy image, illustrate that PB/N, P, S@PC-CS composite distributes very uniformly on the substrate surface, which is hoped to be very attractive for determination of hydrogen peroxide (H2O2). Due to synergistic effect between PB and N, P, S@PC, the PB/N, P, S@PC-CS/GC electrode exhibited excellent conductive and electrocatalytical activity towards H2O2. Under a low applied potential of -0.174V, H2O2 could be linearly detected from 0.4µM to 2.0mM with a low detection limit of 0.2µM (S/N=3) and fast response time of 2s. These results indicate that the electrochemical sensor prepared with PB/N, P, S@PC- CS composite has promising applications for real analysis applications of H2O2.

Electrochemical determination of bisphenol A at ordered mesoporous carbon modified nano-carbon ionic liquid paste electrode.

A simple bisphenol A (BPA) sensor was successfully fabricated based on ordered mesoporous carbon CMK-3 modified nano-carbon ionic liquid paste electrode (CMK-3/nano-CILPE). The nanostructure of CMK-3 and the surface morphologies of modified electrodes were characterized by transmission electron microscopy (TEM) and scanning electron microscopy (SEM). Electrochemical properties of the fabricated electrodes were investigated by cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS). The fabricated sensor displayed excellent electroactivity towards bisphenol A using linear sweep voltammetry (LSV). Experimental conditions influencing the analytical performance of the modified electrode were optimized. Under optimal conditions, the oxidation peak current was proportional to BPA concentration in the range from 0.2 µM to 150 µM with a detection limit of 0.05 µM (S/N=3). This method was successfully used for determination of BPA leached from drinking bottle and plastic bag with good recoveries.

Prussian blue electrodeposited on nano Ag-coated multiwalled carbon nanotubes composite for the determination of hydrogen peroxide.

A prussian blue (PB) electrodeposited on nano Ag-coated multiwalled carbon nanotubes (nano Ag-MWNTs) was reported. Also a PB/nano Ag-MWNTs composite modified glass carbon (GC) electrode was used to investigate the electrochemical behavior concerning the reduction of hydrogen peroxide. The experiment results showed that the PB/nano Ag-MWNTs/GC electrode had a wide linear range, a fast response time and high sensitivity toward the electrocatalytic reduction of hydrogen peroxide. PB and nano Ag-MWNTs had a synergistic electrocatalytic effect toward the reduction of hydrogen peroxide. The PB/nano Ag-MWNTs/GC electrode exhibited a wide linear response range of 8 x 10(-8) to 5 x 10(-3) mol/L with a correlation coefficient of 0.998 for the detection of hydrogen peroxide. Also the response time, detection limit (S/N = 3) and sensitivity of the PB/nano Ag-MWNTs/GC electrode were respectively determined to be 2 s, 4 x 10(-8) mol/L and 920 A/mol cm(2). Another attractive characteristic was that the PB/nano Ag-MWNTs/GC electrode showed high stability and reproducibility.

4-{[2-(2,4-Dinitro-phen-yl)hydrazinyl-idene]meth-yl}phenol ethanol hemisolvate.

In the title compound, C(13)H(10)N(4)O(5)·0.5C(2)H(5)OH, the two benzene rings form a dihedral angle of 4.29 (9)°. The ethanol solvent mol-ecule was treated as disordered between two orientations related by symmetry (center of inversion), with occupancies fixed at 0.5. The crystal packing, stabilized by inter-molecular O-H⋯O and N-H⋯O hydrogen bonds and π-π inter-actions [indicated by the short distance of 3.7299 (7) Šbetween the centroids of benzene rings from neighbouring mol-ecules], exhibits short inter-molecular O⋯O contacts of 2.8226 (3) Å.

(E)-2-[1-(3-Chloro-4-fluoro-phen-yl)ethyl-idene]hydrazinecarbothio-amide.

In the crystal of the title compound, C(9)H(9)ClFN(3)S, the molecules are inter-connected by N-H⋯S and N-H⋯F hydrogen bonds. There are two different N-H⋯S hydrogen bond: the stronger one links mol-ecules into infinite chains along the b axis with graph-set motif C(4), while the weaker N-H⋯S hydrogen bond combines with the previous one into an R(2) (2)(8) network. Moreover, the chains are linked into layers parallel to (102) by weak N-H⋯F hydrogen bonds, which form an R(2) (2)(22) ring motif. In addition, there are also weak π-π inter-actions between the benzene rings of adjacent mol-ecules [centroid-centroid distance = 3.8997 (15) Å].

[N'-(3-Meth-oxy-2-oxidobenzyl-idene)nicotinohydrazidato]diphenyl-tin(IV).

The asymmetric unit of the title compound, [Sn(C(6)H(5))(2)(C(14)H(11)N(3)O(3))], contains two crystallographically independent mol-ecules that differ predominantly in the torsion of the phenyl rings. In both mol-ecules, the Sn(IV) ion is in a distored trigonal-bipyramidal geometry. The Sn-O distances are in the range 2.055 (2)-2.143 (2) Å.

Low-potential nicotinamide adenine dinucleotide detection at a glassy carbon electrode modified with toluidine blue O functionalized multiwall carbon nanotubes.

The toluidine blue O (TBO) functionalized multiwall carbon nanotubes (MWNTs) nanomaterials (TBO-MWNTs) were prepared by assembling TBO onto the surface of a MWNTs modified glassy carbon (GC) electrode. Also TBO-MWNTs modified GC electrodes exhibiting a strong and stable electrocatalytic response toward beta-nicotinamide adenine dinucleotide (NADH) were described. Compared with a bare GC electrode, the TBO-MWNTs modified GC electrodes could decrease the oxidization overpotential of NADH by 730 mV, with a peak current at 0.0 V, since there was a positively synergistic electrocatalytic effect between the MWNTs and TBO toward NADH. Furthermore, the TBO-MWNTs modified GC electrodes had perfect performances, such as a low detection limit (down to 0.5 microM), being very stable (the current diminutions is lower than 6% in a period over 35 min), a fast response (within 3 s), and a wide linear range (from 2.0 microM to 3.5 mM). Such an ability of TBO-MWNTs to promote the NADH electron-transfer reaction suggests great promise for dehydrogenase-based amperometric biosensors.