Effect of polycyclic aromatic hydrocarbons on detection sensitivity of ultratrace nitroaromatic compounds

Polycyclic aromatic hydrocarbons (PAHs) with different numbers of pi-electrons and geometric symmetry of pi-systems, including anthracene, phenanthrene, pyrene, triphenylene, perylene, benzo[ghi]perylene, and coronene, were chosen to modify glassy carbon electrodes (GCEs) by self-assembling. The self-assembled monolayer of PAHs was investigated by STM and was used in the electrochemical detection of nitroaromatic compounds (NACs). The results indicate that PAH-modified GCE shows higher sensitivity to NACs than an unmodified one. Among the seven different PAHs, coronene-modified GCE exhibits the highest sensitivity to 2,4,6-trinitrotoluene and 1,3,5-trinitrobenzene.     

Electrochemical Behavior of Heteropoly Acid Anions Adsorbed in Electrodes Modified with Mesoporous Molecular Sieve Silica

Heteropoly acid H4SiW12O48 (denoted as SiW12) was assembled with the mesoporous materials MCM-41 modified with 3-aminopropyltriethoxysilane (APTES) (denote MCM-41((m))). The electrochemical behavior of SiW12/MCM-41((m)) complexes-based electrode indicated SiW12 anion was adsorbed by MCM-41((m)). In MCM-41((m)) electrode, large voltammetric waves, showing that the electrostatic bound ions adsorbed in MCM-41((m)) were electrochemically active. The potential application as amperometric sensors for nitrite is anticipated.     

Electrochemical strategy with zeolitic imidazolate framework‐8 and ordered mesoporous carbon for detection of xanthine

An accurate, safe, environmentally friendly, fast and sensitive electrochemical biosensors were developed to detect xanthine in serum. The metal‐organic framework ZIF‐8 was synthesised and elemental gold was supported on the surface of ZIF‐8 by reduction method to synthesise Ag‐ZIF‐8. The mesoporous carbon material and the synthesised Ag‐ZIF‐8 were, respectively, applied to a glassy carbon electrode to construct biosensors. The constructed biosensor has a good linear relation in the range of 1–280 μmol l⁻¹ of xanthine and the detection limit is 0.167 μmol l⁻¹. The relative standard deviation value in serum samples was <5%, and the recoveries were 96–106%, indicating the good selectivity, stability and reproducibility of this electrochemical biosensor.Inspec keywords: zeolites, electrochemical sensors, voltammetry (chemical analysis), mesoporous materials, biosensors, gold, reduction (chemical), nanosensors, nanofabrication, organic compounds, electrochemical electrodes, carbon, nanoparticlesOther keywords: xanthine, detection limit, serum samples, zeolitic imidazolate framework‐8, sensitive electrochemical biosensors, metal‐organic framework ZIF‐8, elemental gold, reduction method, mesoporous carbon material, glassy carbon electrode, linear relation, ordered mesoporous carbon, Ag, C     

Selective electrochemical detection of dopamine based on molecularly imprinted poly(5-amino 8-hydroxy quinoline) immobilized reduced graphene oxide

The dopamine-imprinted conducting polymer film of 5-amino 8-hydroxy quinoline (AHQ) was electrodeposited on reduced graphene oxide (rGO)-modified glassy carbon (GC) electrode and was applied as a molecular recognition element for the selective determination of dopamine. The molecularly imprinted polymer (MIP)-modified electrode showed an excellent affinity towards dopamine due to the presence of imprinted site through hydrogen bonding interaction between dopamine and poly (AHQ) membrane. The molecular recognition ability of MIP-modified electrode was analyzed by cyclic voltammetric and differential pulse voltammetric techniques. The most stable geometry of the template–monomer complex in the pre-polymerization mixture was calculated by computational approaches. The rGO modification augmented both surface area and electron transfer kinetics of the bare electrode. The GC/rGO/MIP electrode possessed 2.83 fold current enhancements when compared to GC/MIP electrode, indicating the improvement in sensitivity due to rGO modification. The limit of detection and sensitivity of GC/rGO/MIP electrode was observed to be 32.7 nM and 13.3 AM^?1 cm^?2, respectively. The imprinting methodology provided an exceptional selectivity towards the detection of dopamine even in the presence of high concentration of possible physiological interferents. Moreover, the fabricated electrode was successfully employed for the detection of dopamine in human blood plasma samples proving the effectiveness of the sensor for the sensitive detection of dopamine from real samples.     

Poly-cobalt[tetrakis(o-aminophenyl)porphyrin] nanowire and single-walled carbon nanotube for the analysis of hydrogen peroxide

Nanowires of poly-cobalt[tetrakis(o-aminophenyl)porphyrin] (PCoTAPPNW) were fabricated by electrochemical polymerization by the cyclic voltammetric method in anodic aluminum oxide membranes. A glassy carbon electrode (GCE) modified by PCoTAPPNW and single-walled carbon nanotubes (SWNT) without any binder was investigated with voltammetric methods in phosphate buffer saline (PBS) at pH 7.4. The PCoTAPPNW + SWNT/GCE exhibited strongly enhanced voltammetric and amperometric sensitivity towards hydrogen peroxide (H2O2), which shortened the response time (< 5 seconds), showed detection limit of 1.0 microM and enhanced the sensitivity for H2O2 detection with 194 microA mM(-1) cm(-2). The PCoTAPPNW + SWNT/GCE can be used to monitor H2O2 at very low concentration in physiological pH as an efficient electrochemical H2O2 sensor.     

Electrochemical behavior of L-cysteine and its detection at ordered mesoporous carbon-modified glassy carbon electrode

In this paper, the electrochemical behavior of L-cysteine (CySH) was investigated thoroughly at an ordered mesoporous carbon-modified glassy carbon (OMC/GC) electrode. The voltammetric studies showed there were three anodic peaks for the electrooxidation of CySH in the pH range of 2.00-5.00; however, one peak disappeared above pH 5.00. This behavior has never been reported before. Through the studies of the effect of pH on the distribution fractions (delta) of the four chemical species of CySH, we conclude only CySH2+ (H3A+) and CyS- (HA-) are the electroactive substances and should be responsible for the electrooxidation of CySH. And for the first time, we successfully established the exact and systemic mechanisms based on the electroactive species to explain CySH oxidation at different pH values. On the other hand, a sensitive CySH sensor was developed based on an OMC/GC electrode, which shows a large determination range (18-2500 micromol L(-1)), a high sensitivity (23.6 microA mmol L(-1)), and a remarkably low detection limit (2.0 nmol L(-1), which is the lowest value ever reported for direct CySH determination on the electrodes) at pH 2.00. At pH 7.00, the modified electrode can be still used to readily detect CySH in the range of the physiological levels. These make OMC/GC electrode a promising candidate for efficient electrochemical sensors for the detection of CySH.     

资源化利用铁尾矿制备全硅介孔分子筛MCM-41

以鞍山铁尾矿为硅源,CTAB为模板剂,采用水热合成法合成出全硅介孔分子筛MCM-41。采用X射线衍射分析研究了pH值、CTAB与SiO2配比、晶化温度和晶化时间对MCM-41结构的影响,结果表明MCM-41的合成条件为n（CTAB）/n（SiO2）=0.05～0.60,pH值=8～11,晶化时间〉24h,晶化温度60～100℃。TEM可观察到样品具有典型的按六方对称性排列的孔道结构,孔径在2～4nm变化。FT-IR证明了分子筛具有硅氧四面体骨架。     

Enhanced oxidation of diclofenac sodium at a nano-structured electrochemical sensing film constructed by multi-wall carbon nanotubes–surfactant composite

A multi-walled carbon nanotubes (MWNTs)–dihexadecyl hydrogen phosphate (DHP) film-coated glassy carbon electrode (GCE) was fabricated, and the voltammetric determination method of diclofenac sodium was investigated on this modified electrode by using different kinds of electrochemical techniques. The results showed that this nano-structured film electrode exhibits excellent enhancement effects on the electrochemical oxidation of diclofenac sodium. The oxidation peak current of diclofenac sodium at this film-modified electrode increased significantly compared with that at a bare glassy carbon electrode. Based on the experiment outcomes a possible mechanism was proposed and discussed. The proposed method was demonstrated by using diclofenac sodium tablets and the result was satisfying.     

Sensitive determination of uric acid by using graphene quantum dots as a new substrate for immobilisation of uric oxidase

A novel strategy for highly sensitive electrochemical detection of uric acid (UA) was proposed based on graphene quantum dots (GQDs), GQDs were introduced as a suitable substrate for enzyme immobilisation. Uric oxidase (UOx) was immobilised on GQDs modified glassy carbon electrode (GCE). Transmission electron microscope, scanning electron microscopy, cyclic voltammetry and electrochemical impedance spectroscopy techniques were used for characterising the electrochemical biosensor. The developed biosensor responds efficiently to UA presence over the concentration linear range 1–800 μM with the detection limit 0.3 μM. This novel biosensing platform based on UOx/GQDs electrode responded even more sensitively than that based on GCE modified by UOx alone. The inexpensive, reliable and sensitive sensing platform based on UOx/GQDs electrode provides wide potential applications in clinical.Inspec keywords: organic compounds, graphene devices, quantum dots, enzymes, biosensors, biochemistry, electrochemical electrodes, electrochemical sensors, transmission electron microscopy, scanning electron microscopy, voltammetry (chemical analysis), electrochemical impedance spectroscopy, nanomedicine, molecular biophysicsOther keywords: sensitive uric acid determination, graphene quantum dots, uric oxidase immobilisation, electrochemical detection, GQD, enzyme immobilisation, glassy carbon electrode, GCE, transmission electron microscope, scanning electron microscopy, cyclic voltammetry, electrochemical impedance spectroscopy, electrochemical biosensor, C     

Three-dimensional mesoporous gold film to enhance the sensitivity of electrochemical detection

Cell-cell and cell-extracellular matrix (ECM) adhesion are fundamental and important in the development of a cell-based chip. In this study, a novel, simple, rapid, and one-step technique was developed for the fabrication of a uniform three-dimensional mesoporous gold thin film (MPGF) onto a gold (Au) coated glass plate based on an electrochemical deposition method. Scanning electron microscopy images demonstrated that the resulting MPGF electrode had uniformly distributed pores with diameters of about 20 nm. The cyclic voltammetric behavior of [Fe(CN)(6)](4-/3-) coupled onto MPGF and Au electrodes demonstrated that the MPGF electrode had a higher electrocatalytic sensitivity and reversibility than the bare Au electrode. The Arg-Gly-Asp (RGD) sequence containing the peptide was immobilized on the MPGF and bare Au substrates. HeLa cancer cells were then cultured on the RGD peptide layer. The successful immobilization of the peptide and cells was confirmed by atomic force microscopy. The cell proliferation and viability were evaluated by cyclic voltammetry and Trypan blue dyeing assay. These results indicated that the RGD/MPGF modified electrodes showed an electrochemical sensitivity in the detection of cancer cells which is approximately three times higher, especially at low cell density, than RGD/Au electrodes. This much improved sensitivity of the MPGF modified electrode demonstrates the potential for the fabrication of a highly sensitive and low-cost cell-based chip for rapid cancer detection.     

Voltammetric determination of the synthetic pyrethroid insecticide tetramethrin in acetonitrile

The synthetic pyrethroid insecticide tetramethrin may be reduced reversibly (E°' = -1.650 V vs Ag/Ag(+)) in acetonitrile at hanging mercury drop electrodes (HMDE) and glassy carbon electrodes. On the voltammetric time scale, the initial electron-transfer process involves the reversible formation of a radical anion. Data obtained from electron paramagnetic resonance spectroscopy indicate that the unpaired electron of the radical is located within the phthalimide system of the molecule. The radical anion may be further reduced at very negative applied potentials with the number of processes being dependent on the nature of the voltammetric technique. The detection limit (3σ) for the determination of tetramethrin in acetonitrile at a glassy carbon electrode, using differential pulse voltammetry, was found to be 2.1 × 10(-6) M. At a HMDE the detection limit is lower, having a value of 9.6 × 10(-7) M. The limit of determination (10σ) at a glassy carbon electrode is 3.5 × 10(-6) M and at a HMDE is 3.0 × 10(-6) M. Tetramethrin was selectively determined in an insecticide formulation, at a glassy carbon electrode using differential pulse voltammetry, at a concentration (w/v) of 0.34 ± 0.02%. The determined concentration is in good agreement with the stated value of 0.350 ± 0.018% (w/v).     

Synthesis of MCM-41 nanoparticles from stem of common reed ash silica and their application as substrate in electrooxidation of methanol

In this work, stem of common reed ash (SCRA) is introduced as a new source of silica in the preparation of mesoporous materials. Mesoporous silicate MCM-41 nanoparticles were synthesized hydrothermally using sodium silicate prepared from SCRA as a silica source. The characterization of MCM-41was carried out by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), N\(_{2}\) adsorption/desorption (BET) and transmission electron microscopy (TEM). SEM shows that MCM-41 nanoparticles are sphere-like with size in the range of 30–50 nm with some degree of agglomeration. TEM image of the synthesized sample shows the open framework structure of MCM-41. A type IV isotherm can be observed from adsorption/desorption curves, which is the characteristic of mesoporous materials. The prepared MCM-41 nanoparticles were used as substrate to facilitate the oxidation of methanol through the modification with an electroactive species. The modification was achieved by impregnation of MCM-41 pores with \(\hbox {Ni}^{2+}\) ions (Ni-doped MCM-41). A modified carbon paste electrode (CPE) was prepared by mixing Ni-doped MCM-41 with carbon paste (NiMCM-41CPE). Cyclic voltammetry of NiMCM-41CPE shows an increment in current density of methanol oxidation in comparison with CPE in alkaline solution. Moreover, a decrease in the overpotential of methanol oxidation occurred on the surface of modified electrode. The effects of some parameters such as scan rate and methanol concentration are also investigated on the behaviour of NiMCM-41CPE. Also, the heterogeneous electron transfer rate for the catalytic reaction (k) of methanol is calculated.     

Electrocatalytic reduction of H2O2 on thiolate graphene oxide covalently to bonded palladium nanoparticles

The electrocatalytic reduction of hydrogen peroxide on thioalted graphene oxide (t-GO) covalent bonded to palladium nanoparticles was used as the basis of an H2O2 biosensor. Poly (diallydimethylammonium chloride)-coated t-GO-Pd on glassy carbon electrodes was easily and quickly prepared and gave sensitive measurements of H2O2 concentration. The Pd nanoparticles covalently bonded to the thiolated graphene oxide were characterized by transmission electron microscopy, X-ray photoelectron spectroscopy, and energy dispersive X-ray spectroscopy. Comparable results for H2O2 determination were obtained from cyclic voltammetric and amperometric measurements. The proposed H2O2 biosensor exhibited a wide linear range of 10 microM to 10 mM, and a low detection limit of 0.22 microM (S/N = 3), at an applied potential of -0.1 V by the amperometric method.     

Nanostructured electrochemical sensors based on functionalized nanoporous silica for voltammetric analysis of lead, mercury, and copper

We have successfully developed electrochemical sensors based on functionalized nanostructured materials for voltammetric analysis of toxic metal ions. Glycinylurea self-assembled monolayers on mesoporous silica (Gly-UR SAMMS) were incorporated in carbon paste electrodes for the detection of toxic metal ions such as lead, copper, and mercury based on adsorptive stripping voltammetry (AdSV). The electrochemical sensor yields a linear response at a low ppb level of Pb2+ (i.e., 2.5-50 ppb) after a 2-min preconcentration period, with reproducible measurements (%RSD = 3.5, N = 6) and an excellent detection limit (1 ppb). By exploiting the interfacial functionality of Gly-UR SAMMS, the sensor is selective for the target species, does not require the use of a mercury film, and can be easily regenerated in dilute acid solution. The rigid, open, parallel pore structure, combined with suitable interfacial chemistry of SAMMS, also results in fast analysis times (2-3 min). The nanostructured SAMMS materials enable the development of miniature sensing devices that are compact and low cost, have low energy consumption, and are easily integrated into field-deployable units.     

Electrochemiluminescent detection based on solid-phase extraction at tris(2,2'-bipyridyl)ruthenium(II)-modified ceramic carbon electrode

A sensitive electrochemiluminescent detection scheme by solid-phase extraction at Ru(bpy)3(2+)-modified ceramic carbon electrodes (CCEs) was developed. The as-prepared Ru(bpy)3(2+)-modified CCEs show much better long-term stability than other Nafion-based Ru(bpy)3(2+)-modified electrodes and enjoy the inherent advantages of CCEs. The log-log calibration plot for dioxopromethazine is linear from 1.0 x 10(-9) to 1.0 x 10(-4) mol L(-1) using the new detection scheme. The detection limit is 6.6 x 10(-10) mol L(-1) at a signal-to-noise ratio of 3. The new scheme improves the sensitivity by approximately 3 orders of magnitude, which is the most sensitive Ru(bpy)3(2+) ECL method. The scheme allows the detection of dioxopromethazine in a urine sample within 3 min. Since Ru(bpy)3(2+) ECL is a powerful technique for determination of numerous amine-containing substances, the new detection scheme holds great promise in measurement of free concentrations, investigation of protein-drug interactions and DNA-drug interactions, pharmaceutical analysis, and so on.     

Comparison of different methodologies for integration of molecularly imprinted polymer and electrochemical transducer in order to develop a paraoxon voltammetric sensor

In this work a paraoxon voltammetric sensor was introduced. Different methods for integration of molecularly imprinted polymer (MIP) and electrochemical transducer were investigated. Three techniques including MIP particles embedding in the carbon paste (CP) (MIP-CP), coupling of MIP with the glassy carbon electrode (GC) surface by using poly epychloro hydrine (PECH) (MIP/PECH-GC) and MIP/graphite mixture thin layer attachment onto the glassy carbon electrode (MIP/Graphite-PECH-GC) were tested. The prepared electrodes were applied for paraoxon measurement by using a three-step procedure including analyte extraction in the electrode, electrode washing and electrochemical measurement of paraoxon. The washing of electrodes, after paraoxon extraction, led to high selectivity of electrode for paraoxon. It was found that MIP-CP electrode had higher response to paraoxon in comparison to other tested electrodes. Besides, the washing process decreased response magnitude of MIP/PECH-GC and MIP/Graphite-PECH-GC but, the response of MIP-CP was not affected considerably by the washing. Parathion was chosen to evaluate the selectivity of MIP based sensors. It was proved that the MIP-CP had better selectivity, wider linear range and lower detection limit in comparison to other tested electrodes. The developed MIP-CP electrode was used as a high selective sensor for paraoxon determination in water and vegetable samples.     

Steam-assisted crystallization of TPA+-exchanged MCM-41 type mesoporous materials with thick pore walls

Hierarchical MCM-41/MFI composites were synthesized through ion-exchange of as-made MCM-41 type mesoporous materials with tetrapropylammonium bromide and subsequent steam-assisted recrystallization. The obtained samples were characterized by powder X-ray diffraction (XRD), UV–vis diffuse reflectance spectroscopy, scanning electron microscopy (SEM), transmission electron microscopy (TEM), thermogravimetric analysis, FT-IR, ¹H–¹³C CP/MAS and nitrogen adsorption–desorption. The XRD patterns show that the MCM-41/MFI composite possesses both ordered MCM-41 phase and zeolite MFI phase. SEM and TEM images indicate that the recrystallized materials retained the mesoporous characteristics and the morphology of as-made mesoporous materials without the formation of bulky zeolite, quite different from the mechanical mixture of MCM-41 and MFI structured zeolite. Among others, lower recrystallization temperature and the introduction of the titanium to the parent materials are beneficial to preserve the mesoporous structure during the recrystallization process.     

MWCNTs/Cu(OH)2 nanoparticles/IL nanocomposite modified glassy carbon electrode as a voltammetric sensor for determination of the non-steroidal anti-inflammatory drug diclofenac

This paper describes the development and utilization of a new nanocomposite consisting of Cu(OH)₂ nanoparticles, hydrophobic ionic liquid 1-ethyl-3-methylimidazolium hexafluorophosphate (EMIMPF₆) and multiwalled carbon nanotubes for glassy carbon electrode modification. The nanocomposite was characterized by transmission electron microscopy (TEM), scanning electron microscopy (SEM) along with energy-dispersive X-ray spectroscopy (EDX). The modified electrode was used for electrochemical characterization of diclofenac. Using differential pulse voltammetry, the prepared sensor showed good sensitivity and selectivity with low overpotential for the determination of diclofenac in the range from 0.18 to 119 μM, with a detection limit of 0.04 μM. Electrochemical studies suggested that the MWCNTs/Cu(OH)₂ nanoparticles/IL nanocomposite modified electrode provided a synergistic augmentation on the voltammetric behavior of electrochemical oxidation of diclofenac, which was indicated by the improvement of anodic peak current.     

Electrochemical behavior of two and one electron redox systems adsorbed on to micro- and mesoporous silicate materials: Influence of the channels and the cationic environment of the host materials

Electrochemical behavior of two electron redox system, phenosafranine (PS⁺) adsorbed on to micro- and mesoporous materials is investigated by cyclic voltammetry and differential pulse voltammetry using modified micro- and mesoporous host electrodes. Two redox peaks were observed when phenosafranine is adsorbed on the surface of microporous materials zeolite-Y and ZSM-5. However, only a single redox peak was observed in the modified electrode with phenosafranine encapsulated into the mesoporous material MCM-41 and when adsorbed on the external surface of silica. The observed redox peaks for the modified electrodes with zeolite-Y and ZSM-5 host are suggested to be primarily due to consecutive two electron processes. The peak separation ΔE and peak potential of phenosafranine adsorbed on zeolite-Y and ZSM-5 were found to be influenced by the pH of the electrolyte solution. The variation of the peak current in the cyclic voltammogram and differential pulse voltammetry with scan rate shows that electrodic processes are controlled by the nature of the surface of the host material. The heterogeneous electron transfer rate constants for phenosafranine adsorbed on to micro- and mesoporous materials were calculated using the Laviron model. Higher rate constant observed for the dye encapsulated into the MCM-41 indicates that the one-dimensional channel of the mesoporous material provides a more facile micro-environment for phenosafranine for the electron transfer reaction as compared to the microporous silicate materials. The stability of the modified electrode surface was investigated by multisweep cyclic voltammetry.     

Chemical fluid deposition of monometallic and bimetallic nanoparticles on ordered mesoporous silica as hydrogenation catalysts

A simple and green method of depositing monometallic (Ru, Rh, Pd) and bimetallic nanoparticles (Ru-Rh, Ru-Pd and Rh-Pd) on an ordered mesoporous silica support (MCM-41) in supercritical carbon dioxide (scCO2) is described. Metal acetylacetonates were used in the experiments as CO2-soluble metal precursors. Suitable temperature and pressure conditions for synthesizing each kind of nanoparticles were applied in this study. The characterizations of these nanocomposites were performed by transmission electron microscopy (TEM), X-ray diffraction (XRD) and energy dispersive X-ray spectroscopy (EDS). The nanoparticles had average sizes varying from 2 nm to 8 nm. The Ru nanoparticles were clearly shown to be inside the mesopores of MCM-41 from the TEM image. These nanocomposites used as catalysts for hydrogenation was demonstrated. The efficiency of the scCO2 prepared Ru/MCM-41 catalyst was nearly 8 times than that of a Ru/MCM-41 catalyst prepared by conventional impregnation method.