Metallohosts with a heart of carbon

Single-crystal X-ray diffraction studies have confirmed that Ni(3)S(3)-based molecular bowls prepared in one-pot reactions capture either CH(2)Cl(2) or C(60). The nature of the pendant substituents (naphthalen-2-ylmethyl, benzyl, or ethyl) around the rim of the bowl dictates the formation of a 1:1 (bowl host-C(60) guest) or 2:1 (capsule host-C(60) guest) architecture. In CDCl(3), the trimeric complexes were found to be in equilibrium with dimeric analogues. For the naphthalen-2-ylmethyl-substituted host, NMR spectroscopic titration data confirmed a 1:1 host-C(60) guest complex in 1,2-Cl(2)C(6)D(4) solution.     

Electrochemical sensor for Baicalein using a carbon paste electrode doped with carbon nanotubes

We report on the voltammetric determination of the flavonoid Baicalein by using a carbon paste electrode that was doped with multi-walled carbon nanotubes. The resulting sensor exhibits excellent redox activity towards Baicalein due to the large surface area and good conductivity of the electrode. Cyclic voltammetry at various scan rates was used to investigate the redox properties of Baicalein. At the optimum conditions, the sensor displays a linear current response to Baicalein in the 0.02–10 μM concentration range, with a limit of detection of 4.2 n M. The method was successfully applied to the determination of Baicalein in spiked human blood serum samples and in a Chinese oral liquid.

Amperometric thrombin aptasensor using a glassy carbon electrode modified with polyaniline and multiwalled carbon nanotubes tethered with a thiolated aptamer

A nanocomposite consisting of polyaniline and multiwalled carbon nanotubes was tethered with a thiolated thrombin-specific aptamer and placed on a glassy carbon electrode (GCE) to obtain a biosensor for thrombin that has a limit of detection of 80 fM. Tethering was accomplished via a thiol-ene reaction between thiolated thrombin aptamer (TTA) and oxidized polyaniline (PANI) that was chemically synthesized in the presence of solution-dispersed multiwalled carbon nanotubes (MWCNTs). The modified GCE exhibits a pair of well-defined redox peaks (at 50/?25 mV) of self-doped PANI in neutral solution, and the tethered TTA-thrombin interaction gives a decreased electrochemical signal. Cyclic voltammetry, scanning electron microscopy and ultraviolet visible spectroscopy were used to characterize the film properties. This amperometric aptasensor is sensitive, selective and reproducible. It was applied to the determination of thrombin in spiked human serum (0.2 to 4 nM) and gave recoveries that ranged from 95 to 102%.

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Graphical abstract A nanocomposite consisting of polyaniline (PANI) and multiwalled carbon nanotubes (MWCNTs) was tethered with a thiolated thrombin aptamer (TTA) and placed on a glassy carbon electrode (GCE) to obtain a biosensor for thrombin that has a 80 f. detection limit.

     

Electrocatalytic reduction of carbon monoxide with a photocell

It has been shown that CO can be reduced with an electrochemical photocell to methanol in the presence of ethanol and pentachlorochromate(III), bis(oxalato)chromate(III) or iron(III)-tiron complex. The photocell was composed of n-CdS and Everitt's salt-modified platinum electrodes, operating as the photoanode and the cathode, respectively. The current efficiency was 1.0–5.2%, i.e. very low compared with the value (about 100%) obtained in the catalytic system containing methanol instead of ethanol, which was attributed to lower efficiency of the CO uptake by the metal complex-ethanol catalytic system.     

Electrochemical determination of acetaminophen using a glassy carbon electrode coated with a single-wall carbon nanotube-dicetyl phosphate film

Single-wall carbon nanotubes (SWNT) were dispersed into water in the presence of dicetyl phosphate (DCP), and then a SWNT-DCP film-coated glassy carbon electrode (GCE) was constructed. The electrochemical behavior of acetaminophen at bare GCE and SWNT-DCP modified GCE were compared, suggesting that the SWNT-DCP-modified GCE significantly enhances the oxidation peak current of acetaminophen. A sensitive and simple electrochemical method with a good linear relationship in the range of 1.0 × 10⁻⁷–2.0 × 10⁻⁵ mol L⁻¹, was developed for the determination of acetaminophen. The detection limit is 4.0 × 10⁻⁸ mol L⁻¹ for 3-min accumulation. This method was successfully demonstrated with tablets.     

Quantification of methyldopa in pharmaceuticals using a glassy carbon electrode modified with carbon nanotubes

The quantification of methyldopa in pharmaceuticals has been carried out using a glassy carbon electrode(GCE) modified with multi-walled carbon nanotubes(MWCNTs). Methyldopa exhibited a quasi-reversible response with a peak potential separation of 473 m V on a bare GCE. However, the cyclic voltammetric behaviour of methyldopa was improved with the increase of the amount of MWCNTs. It was also shown that the electrocatalytic activity of the electrode towards the response of methyldopa was higher with larger amount of film on the surface. The results showed that the peak current was proportional to the concentration of methyldopa with a linear dynamic range of 0.005–0.388 mmol/L and a detection limit of 1.0 nmol/L was obtained using square wave voltammetry. The experimental data showed that the detection limit of methyldopa and peak separation from interfering compounds such as ascorbic acid(AA) and uric acid(UA) were improved using the proposed procedure. The method was successfully applied for the determination of methyldopa in pharmaceuticals.     

Voltammetric lidocaine sensor by using a glassy carbon electrode modified with porous carbon prepared from a MOF,and with a molecularly imprinted polymer

The work describes a hybrid electrochemical sensor for highly sensitive detection of the anesthetic lidocaine (LID). Porous carbon (PC) was synthesized from an isoreticular metal-organic framework-8 (IRMOF-8) and drop cast onto a glassy carbon electrode (GCE). A layer of a molecularly imprinted polymer (MIP) layer was then fabricated in situ on the modified GCE by electro-polymerization, with LID acting as the template and resorcinol as the functional monomer. Hexacyanoferrate is used as an electrochemical probe. The electrical signal (typically acquired at 0.335 V vs. SCE) increases linearly in the 0.2 pM to 8 nM LID concentration range, with a remarkable 67 fM detection limit (at an S/N ratio of 3). The sensor is stable and selective. Eventually, rapid and accurate detection of LID in spiked real samples was successfully realized.

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Graphical abstract ?

     

Sensing Lorazepam with a glassy carbon electrode coated with an electropolymerized-imprinted polymer modified with multiwalled carbon nanotubes and gold nanoparticles

We report on an electrode for the amperometric determination of lorazepam. A glassy carbon electrode was coated with a molecular imprint made by electropolymerization of ortho-phenylenediamine and filled with multiwalled carbon nanotubes and gold nanoparticles, which enhances the transmission of electrons. The sensor was studied with respect to its response to hexacyanoferrate (III) as a probe and by electrochemical impedance spectroscopy, cyclic voltammetry and square wave voltammetry. The linear response range to Lorazepam is from 0.5 nM to 1.0 nM and from 1.0 nM to 10.0 nM, with a detection limit of 0.2 nM (at an S/N of 3). The electrode was successfully applied to determine Lorazepam in spiked human serum.

Electrochemical investigation of a glassy carbon electrode modified with carbon nanotubes decorated with (poly)crystalline gold

Multiwalled carbon nanotubes with nanosized sputtered gold were used to modify a glassy carbon electrode (GCE). The substrate was characterized by scanning electron microscopy (SEM), X-ray diffraction, cyclic voltammetry and amperometry. SEM micrographs indicated an uniform coverage of the carbon nanotubes with nanosized (poly)crystalline gold. Cyclic voltammetry reveals that peak separation of the unmodified GCE in the presence of 1?mM ferricyanide is 131?mV, but 60?mV only for the modified GCE. In addition, the oxidation of NADH (1?mmol?L^?1 solution) begins at negative potentials (around ?100?mV vs. Ag/AgCl), and the anodic peak potential (corresponding to the irreversible oxidation of NADH) is found at +94?mV. The effect of pH on the electrocatalytic activity was studied in the range from 5.4 to 8.0. The relationship between the anodic peak potential and the pH indicated a variation of ?33.5?mV/pH which is in agreement with a two-electron and one-proton reaction mechanism. Amperometry, performed at either ?50 or +50?mV vs. an Ag/AgCl reference electrode, indicates that the modified electrode is a viable amperometric sensor for NADH. At a working potential of +50?mV, the response to NADH is linear in the concentration range from 1 to 100???mol?L^?1, with an RSD of 6% (n?=?4).

Determination of microcystin-LR with a glassy carbon impedimetric immunoelectrode modified with an ionic liquid and multiwalled carbon nanotubes

We report on a sensitive, simple, label-free impedance-based immunoelectrode for the determination of microcystin-LR (MCLR). The surface of the electrode was modified with a composite made from multiwalled carbon nanotubes and an ionic liquid, and with immobilized polyclonal antibody against MCLR. Cyclic voltammetry and impedance spectroscopy were applied to characterize the modified electrode. It is found that the multi-walled carbon nanotubes act as excellent mediators for the electron transfer between the electrode and dissolved hexacyanoferrate redox pair, while the ionic liquid renders it biocompatible. The method exhibits a wide linear range (0.005 μg?L-1 to 1.0 μg?L-1), a low detection limit (1.7 ng?L-1) and a long-term stability of around 60 days. The ionic liquid 1-amyl-2,3-dimethylimidazolium hexafluorophosphate gave the best impedimetric response. The new immunoelectrode is sensitive, stable, and easily prepared. It has been successfully applied to the determination of MCLR in water samples.

Multi-wall carbon nanotubes with nitrogen-containing carbon coating

Polyaniline coating was deposited on the surface of multi-wall carbon nanotubes of Russian and Taiwanese origin in situ during the polymerization of aniline. The deposited polyaniline film was subsequently carbonized under an inert atmosphere at various temperatures to produce coaxial coating of the carbon nanotubes with nitrogen-containing carbon. The new materials were investigated by infrared and Raman spectroscopies, which demonstrated the conversion of the polyaniline coating to a carbonized structure. X-ray photoelectron spectroscopy proved that the carbonized overlayer contains nitrogen atoms in various covalent bonding states. Transmission electron microscopy confirmed the coaxial structure of the composites. The Brunauer-Emmett-Teller method was used to estimate the specific surface area, the highest being 272 m² g^?1. The conductivity of 0.9–16 S cm^?1 was measured by the four-point method, and it was only a little affected by the carbonization of the polyaniline coating.     

Voltammetric determination of tinidazole using a glassy carbon electrode modified with single-wall carbon nanotubes.

An electrochemical method based on a single-wall carbon nanotubes (SWNTs) film-coated glassy carbon electrode (GCE) was described for the determination of tinidazole. In a 0.1 M Britton-Robinson buffer with a pH of 10.0, tinidazole yields a very sensitive and well-defined reduction peak at -0.78 V (vs. SCE) on a SWNTs-modified GCE. Compared with that on a bare GCE, the reduction peak of tinidazole increases significantly on the modified GCE. Thus, all of the experimental parameters were optimized and a sensitive voltammetric method is proposed for tinidazole determination. It is found that the reduction peak current is proportional to the concentration of tinidazole over the range from 5 x 10(-8) to 4 x 10(-5) M, and that the detection limit is 1 x 10(-8) M at 3 min open-circuit accumulation. This new analysis method was demonstrated with tinidazole drugs.     

Amperometric hydrazine sensor using a glassy carbon electrode modified with gold nanoparticle-decorated multiwalled carbon nanotubes

Microchimica Acta - Gold nanoparticles (AuNP) were deposited on the surface of multiwalled carbon nanotubes (MWCNT) by in-situ thermal decomposition of gold acetate under solvent and reducing agent...     

Electrochemical determination of paraquat using a glassy carbon electrode decorated with pillararene-coated nitrogen-doped carbon dots

An electrochemical sensor(carboxylatopillar[5]arene-coated nitrogen-doped carbon dots, namely CCDs)based on carboxylatopillar[5]arene(CP[5]) functionalized nitrogen-doped carbon dots(N-CDs) has been developed in a facile and economic manner. To improve the performance of this electrochemical sensor in pesticide detection, the optimal solution p H(p H 7) and loading amount of CCDs on the electrode(0.50 mg/m L) have been determined. By virtue of the good conductivity of N-CDs and the molecular rec...     

Biosensor based on a glassy carbon electrode modified with tyrosinase immmobilized on multiwalled carbon nanotubes

We describe a biosensor for phenolic compounds that is based on a glassy carbon electrode modified with tyrosinase immobilized on multiwalled carbon nanotubes (MWNTs). The MWNTs possess excellent inherent electrical conductivity which enhances the electron transfer rate and results in good electrochemical catalytic activity towards the reduction of benzoquinone produced by enzymatic reaction. The biosensor was characterized by cyclic voltammetry, and the experimental conditions were optimized. The cathodíc current is linearly related to the concentration of the phenols between 0.4???M and 10???M, and the detection limit is 0.2???M. The method was applied to the determination of phenol in water samples.

Metastable intermolecular charge-transfer complexes with a pentavalent carbon atom

A novel type of metastable complexes of metal (such as Na) atoms with a super-fluorinated carbon molecule is investigated, with a carbon atom exhibiting a unique, pentavalent character. It is induced by the charge transfer from the alkali metal component, followed by a geometric compression of the ion pair system. Analysis of the electron-density distribution confirms the real chemical nature of the extra C-F bond. Structure and stability of the system are characterized ab initio, and a spectrum of electronic perturbations is considered. The ways of forming the systems are discussed, and the spectroscopic parameters are predicted, facilitating their detection in experiments.     

Voltammetric sensing of sulfamethoxazole using a glassy carbon electrode modified with a graphitic carbon nitride and zinc oxide nanocomposite

A voltammetric sensor is described for the determination the antibiotic sulfamethoxazole (SMZ). It is based on the use of a glassy carbon electrode (GCE) modified with a nanocomposite prepared from graphitic carbon nitride and zinc oxide (g-C₃N₄/ZnO). The nanorod-like ZnO nanostructure were synthesized sonochemically. The g-C₃N₄/ZnO nanocomposite was then prepared by mixing g-C₃N₄ with ZnO, followed by ultrasonication. The morphology and structure of the nanocomposite were characterized by X-ray diffraction, Fourier-transform infrared spectroscopy and transmission electron microscopy. Under the optimal conditions, the response of the electrode, typically measured between 0.8 and 0.9 V (vs. Ag/AgCl), increases linearly in the 20 nM to 1.1 mM SMZ concentration range, and the lower detection limit is 6.6 nM. This is better than that of many previously reported sensors for SMZ. The modified electrode is highly selective, well reproducible and maintains its activity for at least 4 weeks. It was applied to the determination of SMZ in spiked human blood serum samples in with satisfactory results.

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Graphical abstract Schematic presentation of the voltammetric sensor for sulfamethoxazole. It consists of a glassy carbon electrode modified with a nanocomposite prepared from graphitic carbon nitride (g-C₃N₄/ZnO) that was supported with zinc oxide nanorods.

     

A glutathione biosensor based on a glassy carbon electrode modified with CdO nanoparticle-decorated carbon nanotubes in a nafion matrix

A nanocomposite consisting of cadmium oxide decorated with carbon nanotubes (CdO.CNT NC) was prepared by a wet-chemical technique, and its optical, morphological, and structural properties were characterized by FTIR, UV/Vis, FESEM coupled to XEDS, XPS, and XRD methods. A flat glassy carbon electrode was modified with the nanocomposite to obtain a sensor for L-glutathione (GSH) which displays improved sensitivity, a large dynamic range and good long-term stability. The calibration plot (best acquired at a voltage of 0.5 V) is linear (r ² = 0.99) in the 0.1 nM to 0.01 M GSH concentration range. The detection limit is as low as 30.0 pM, and the sensitivity is ~9.49 μA?μM^?1?cm^?2. To the best of our knowledge, this is the first report on the determination of GSH using such a modified glassy carbon electrode (GCE) in combination with I-V method. The GCE was applied to the selective determination of GSH in spiked rabbit serum samples and gave acceptable results.

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Graphical abstract A selective glutathione biosensor based on wet-chemically prepared CdO.CNT/Nafion/GCE was fabricated by reliable I-V method and shows good analytical parameters such as high sensitivity, low detection limit, long-term stability, and large dynamic range.