Trace-level sensing of creatine in real sample using a zwitterionic molecularly imprinted polymer brush grafted to sol-gel modified graphite electrode

Zwitterionic molecularly imprinted polymeric chains were tethered to the sol-gel modified graphite electrode in brush pattern of high density, for the quantitative estimation of creatine at trace level, without any cross reactivity, in real samples. The modified electrode was activated by preanodization at + 1.4 V (vs. saturated calomel electrode) for the fast ion-exchange recapture of creatine, under mild basic condition (pH 7.1). The detection limit was as low as 1.3 µg mL^− 1 (signal/noise = 3) employing differential pulse, cathodic stripping technique.     

2D-titanium carbide (MXene) based selective electrochemical sensor for simultaneous detection of ascorbic acid,dopamine and uric acid

Two-dimensional (2D) titanium carbide (MXene) nanosheets exhibited excellent conductivity,flexibility,high volumetric capacity,hydrophilic surface,thermal stability,etc.So,it has been exploited in various applications.Herein,we report synthesis of mixed phase 2D MXene as a catalytic material for simultaneous detection of important biomolecules such as ascorbic acid (AA),dopamine (DA) and uric acid (UA),Crystalline structure,surface morphology and elemental composition of mixed phase titanium carbide (Ti-C-Tx) MXene (Tx =-F,-OH,or-O) nanosheets were confirmed by X-ray diffraction (XRD),Raman spectroscopy,high-resolution transmission electron microscopy (HR-TEM),high-resolution scanning electron microscopy (HR-SEM) and Energy-dispersive X-ray spectroscopy (EDS) mapping analysis.Furthermore,Ti-C-Tx modified glassy carbon electrode (GCE) was prepared and its electrochemical properties are studied by cyclic voltammetry (CV) and differential pulse voltammetry (DPV).It was found that Ti-C-Tx modified GCE (Ti-C-Tx/GCE) showed excellent electrocatalytic activity and separated oxidation peaks of important biomolecules such as AA (at 0.01 V),DA (at 0.21 V) and UA (at 0.33 V).Also,Ti-C-Tx/GCE sensor is enabled their simultaneous detection in physiological pH from 100 to 1000 μM for AA,0.5-50 μM for DA and 0.5-4 μM & 100-1500 μM for UA.The limit ofdetection's (LOD) was estimated as 4.6 μM,0.06 μM and 0.075 μM for AA,DA and UA,respectively.Moreover,real sample analysis indicated that spiked AA,DA and UA can be determined accurately by Ti-C-Tx/GCE with the recovery ratio in the range between 100.5％-103％ in human urine samples.The proposed Ti-C-Tx modified electrode exhibited good stability,selectivity and reproducibility as an electrochemical sensor for the detection ofAA,DA and UA molecules.     

Synthesis,characterization, and voltammetric hydrogen peroxide sensing on novel monometallic (Ag,Co/MWCNT) and bimetallic (AgCo/MWCNT) alloy nanoparticles

Multiwall carbon nanotube supported (MWCNT) Ag, Co, and Ag-Co alloy nanocatalysts were synthesized at varying metal loadings by borohydride reduction methods without stabilizers to obtain enhanced hydrogen peroxide sensitivity. The resulting materials were characterized employing Scanning electron microscopy (SEM), Energy dispersive X-ray spectroscopy (EDX), and X-ray diffraction (XRD). For electrochemical measurements carried out cyclic voltammetry (CV) and differential pulse voltammetry (DPV), glassy carbon electrode (GCE) was modified with Ag/MWCNT, Co/MWCNT, and Ag-Co/MWCNT alloy nanoparticles. Ag-Co/MWCNT/GCE exhibited the highest performance toward electrochemical oxidation of H₂O₂ in 0.1 M phosphate buffered solution (PBS). Furthermore, the sensitivity and the limit of detection values for Ag-Co/MWCNT/GCE were obtained as 57.14 µA cm^?2 mM^?1and 0.74 µM, respectively. However, the sensitivity values for Ag/MWCNT/GCE, and Co/MWCNT/GCE are 41.66 and 13.88 µA cm^?2 mM^?1, respectively. The LOD values were predicted as 1.84 µM for Ag/MWCNT/GCE and 3.3 µM for Co/MWCNT/GCE.

In addition, the interference experiment indicated that the Ag-Co/MWCNT alloy nanoparticles have good selectivity toward H₂O₂.     

Influence of dopant in the synthesis, characteristics and ammonia sensing behavior of processable polyaniline

Polyaniline (PANI) was synthesized by oxidative polymerization of aniline as well as aniline hydrochloride by ammonium persulfate in the presence of para-toluene sulfonic acid (PTSA). This helped in direct usage of the conducting PANI solution for film casting and use as a device for ammonia gas sensing. Viscosity change with applied shear rate was measured for both the polymers. Solid PANI powder was isolated from its tetrahydrofuran solution by using methanol as non-solvent. Thermogravimetric analysis investigated the thermal properties of the solid PANI salts. Elemental analysis of both PANI synthesized in presence of PTSA and PANI synthesized in presence of HCl and PTSA was investigated. A thin coherent film of both the conducting PANI were deposited on glass slides precoated with poly vinyl alcohol (PVA) crosslinked with maleic acid (MA) and was directly used in the sensor device. The morphology of the deposited films was analyzed by scanning electron micrograph. The films were further characterized by Attenuated total reflectance Fourier transformed infrared spectroscopy, ultra violet-visible spectroscopy and X-ray diffraction analyses. Finally, both the doped PANI films on MA crosslinked PVA coated glass slides were used to measure the conductivity and ammonia gas-sensing characteristics.     

Electrochemical activity of polyaniline based on mixed dopants and cation movement toward high pH region

Two kinds of polyaniline (PANi) films have been comparatively studied for their electrochemical activity in HCl/NaCl aqueous electrolyte. A standard film of PANi/NMP was prepared by casting PANi from N-methyl pyrrolidone (NMP) solution. The other film of PANi/DBS was prepared from PANi dissolved in mixed solution of dodecylbenzene sulfonic (DBS) and dichloroacetic acids. The PANi/NMP film increased in the weight and volume upon oxidation, indicating anion movement. The weight uptake measured by quartz crystal microbalance and strain were approximately agreed with the number and volume of doped anions (Cl⁻) estimated from cyclic voltammogram. On the other hand, PANI/DBS film increased in the weight upon reduction. The correspondence between weight uptake and electronic charges during reduction indicated Na⁺ movement. Although the PANi/NMP showed electrochemical activity at pH < 2, the PANi/DBS was active up to pH5. Namely, the large DBS anion was immobilized in PANi network, resulting in cation movement and higher pH activity.     

Effect of Fe on the synthesis and electrochemical performance of nanostructured MnO2

Different MnO₂ nanostructures were synthesized in stoichiometric KMnO_4/MnSO₄ aqueous solutions in the absence/presence of Fe³⁺ at temperature ranging from 30 °C to 180 °C. The phase structures, morphologies and electrochemical properties of the as-prepared MnO₂ products were investigated using X-ray powder diffraction, scanning electron microscope, N₂ physical adsorption and cyclic voltammetry techniques. The results showed that the presence of Fe³⁺ addition had a significant effect on the phase structural evolution, morphological features and electrochemical properties of the MnO₂ products. Fe³⁺ was found to greatly prevent the epitaxial growth and crystallization of MnO₂ nucleus, which in turn influenced textual characteristics. The electrochemical performance of the nanostructured MnO₂ products had a complex relationship with the phase structures, specific surface area as well as pore characteristics. MnO₂ prepared in the presence of Fe³⁺ (KMF-MnO₂) showed relatively higher specific capacitance compared to that of MnO₂ prepared in the absence of Fe³⁺ (KM-MnO₂). Maximum capacitance of 214 F g⁻¹ was obtained for KMF-MnO₂ prepared at 30 °C at a scan rate of 2 mV s⁻¹ in 0.1 M Na₂SO₄ electrolyte.     

Electrosynthesis and analysis of the electrochemical properties of a composite material: Polyaniline + titanium oxide

The analysis of the electrochemical and spectroscopic properties of a composite material obtained starting from the polyaniline and TiO₂ in H₂SO₄ medium, using cyclic voltamperometry, shows three redox couples characteristic of the different oxidation and reduction states of produced polymer. The electroactivity of the composite in acid medium was better than that obtained in basic medium. The impedance spectroscopy study shows that the resistance of the film increases with the aniline concentration, but is not significantly affected by the amount of TiO₂ incorporated in polymer. The increase of pH decreases the resistance of the films and consequently increases its conductivity.     

Effect of conducting polypyrrole on the transport properties of carbon nanotube yarn

Experiments were conducted to measure the electrical conductivity in three types of pristine and carbon nanotube-polypyrrole (CNT-PPy) composite yarns and its dependence on over a wide temperature range. The experimental results fit well with the analytical models developed. The effective energy separation between localized states of the pristine CNT yarn is larger than that for both the electrochemically and chemically prepared CNT-PPy yarns. It was found that all samples are in the critical regime in the insulator-metal transition, or close to the metallic regime at low temperature. The electrical conductivity results are in good agreement with a Three Dimensional Variable Range Hopping model at low temperatures, which provides a strong indication that electron hopping is the main means of current transfer in CNT yarns at T < 100 K. We found that the two shell model accurately describes the electronic properties of CNT and CNT-PPy composite yarns in the temperature range of 5-350 K.     

Effect of oxygen exposure on the electrical conductivity and gas sensitivity of nanostructured ZnO films

Nanostructured ZnO films (undoped and Ga, Co, Mn doped) were exposed to oxygen (1-80 vol.%) at temperature range of 300-500 °С in order to reveal the ambience-temperature effect on the electrical conductivity. The dominant effect of ambient influence via oxygen absorption was observed: the intensity of conductivity decrease was found to be proportional with temperature and tends to saturate with time. It is demonstrated that oxygen absorption occurs accordingly to diffusion law and the quantifying of oxygen diffusion was realized for different samples. It is revealed that the type of dopant affects the diffusion in ZnO and the tendency to increase the diffusion intensity with dopant content has been observed. After oxygen saturation the reversible effect of oxygen adsorption became dominant and contributed to the film's conductivity. Oxygen exposure undoped ZnO films revealed high sensitivity for oxygen content change in the ambience therefore they have been preceded further for gas sensor design and the detailed investigation of film's sensing properties has been carried out.     

A facile sonochemical approach based on graphene carbon nitride doped silver molybdate immobilized nafion for selective and sensitive electrochemical detection of chromium (VI) in real sample

The hexavalent Chromium (Chromium (VI) (or) Cr⁶⁺) is considered as the most toxic element that directly affects the environment and the human cycle adversely. Therefore, in the present study we proposed a sensitive and selective electrochemical sensor for the detection of Cr⁶⁺ in various water samples using graphene carbon nitride decorated with silver molybdate immobilized with nafion (g-C₃N₄/AgM/Nf) modified glassy carbon electrode (GCE). The nanocomposite was synthesized by sonochemical method and characterized by various analytical and spectroscopic techniques. The g-C₃N₄/AgM/Nf/GCE was exceptional and showed massive electrocatalytic change via the appearance of peaks in amperometric i-t technique. Cr⁶⁺ has a reduction peak appearing at 0.1–0.7 μM, with a low limit of detection of 0.0016 μM, and sensitivity of 65.8 µAµM⁻¹cm⁻². The g-C₃N₄/AgM/Nf/GCE sensor for Cr⁶⁺ exhibited a good selectivity, stability, sensitivity, and reproducibility, which certified that the g-C₃N₄/AgM/Nf/GCE is a promising electrode. The electrochemical sensing method also accessed for the recognition of Cr⁶⁺ in different water samples and showed good feasibility with superior recovery.     

Effect of zirconium doping on ZnO nanostructured thin films and the enhanced ammonia gas sensing activity

Journal of Materials Science: Materials in Electronics - A room temperature gas sensor with excellent stability and a high response has gotten a lot of interest, and there is a huge demand for...     

Adsorption and electropolymerization of toluidine blue on the nanostructured octakis(hydridodimethylsiloxy)octasilsesquioxane surface

Toluidine blue O (TBO) was adsorbed on the octakis(hydridodimethylsiloxy)octasilsesquioxane (Q₈M₈^H) surface. The characterization of the precursor (Q₈M₈^H) and resulting materials obtained by the reaction of Q₈M₈^H and toluidine blue (CTBO) were defined using Fourier transform infrared spectra, nuclear magnetic resonance solid-state ¹³C and Si²⁹ magic angle spinning. The electrochemical polymerization in a glassy carbon electrode was verified by means of a film silsesquioxane formation (FCTBO) using cyclic voltammetry in a potential range of −0.5 to 1.3 V (vs. saturated calomel electrode (SCE)) in a Britton Robinson (B-R) buffer solution (pH 2.0). The cyclic voltammogram of the film exhibits two redox couples with a formal potential of −0.15 and −0.02 V (B-R buffer pH 5). The formal potential shifts linearly in the cathodic direction by increasing the pH solution with a slope of 71 and 57 mV per unit for the first and second couple, respectively. The film was electrochemically very stable.     

Laterally selective adsorption of pH sensing coatings based on neutral red by means of the electric field directed layer-by-layer self assembly method

In this work, electric field directed layer-by-layer assembly is proposed for fabricating patterned sensing coatings. The Neutral Red (NR) colorimetric pH sensitive indicator and the polymers poly(acrylic acid) (PAA) and poly(allylamine hydrochloride) (PAH) which had been already proposed in the past by several groups to incorporate diverse indicators are used here in two different structures with the aim of obtaining selective deposition. The first structure studied combines NR and PAA while the second structure combines both NR and PAH with PAA. The results obtained in this work revealed that the LbL material adsorption over the electrodes was enhanced or even inhibited when applying a specific direct current voltage between them under some other particular fabrication parameters. Particularly, by adjusting to 7 the pH of the solutions used for the fabrication of the films and applying 1.4 V between the electrodes, laterally selective deposition was obtained with both of the pH sensing structures proposed here. This strategy allows the fabrication of pH-sensitive patterned films.     

Studies on the effect of solvents on self-assembly of thioctic acid and Mercaptohexanol on gold

In this article we investigated the effect of solvents (CCl₄, CH₃CN, DMF, ethanol, ethanol-H₂O and H₂O) on self-assembly of Thioctic acid (TA) and Mercaptohexanol (MCH) on gold by cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS). Electrochemical characteristics of TA and MCH self-assembled monolayers (SAMs) formed in different solvents were evaluated by inspecting the ions permeability (interfacial capacitance C and phase angle Ф_1 Hz) and electron transfer capability (current density difference Δi and charge transfer resistance R_ct). Experimental results indicated that the ability of solvents availing the ordering of SAMs was: for TA, CCl₄ > ethanol > CH₃CN > ethanol-H₂O > DMF; for MCH, H₂O > ethanol-H₂O ≈ CCl₄ > ethanol ≈ CH₃CN > DMF. Through relating the C, Ф_1 Hz, Δi and R_ct of SAMs (TA and MCH) with parameters of solvent (polarity E_T^N, solubility parameter δ and octanol/water partition coefficients logP_ow), it was found that solvents with bigger logP_ow (smaller E_T^N and δ) availed the ordering of TA-SAMs but the effect of solvents on MCH self-assembly was complex and MCH-SAMs formed in H₂O (the biggest E_T^N, δ and the smallest logP_ow) and CCl₄ (the smallest E_T^N, δ and the biggest logP_ow) were more ordered than in other solvents.     

Investigation of the microstructure and corrosion performance of a nanostructured titania-containing hybrid silicate film on mild steel

A pre-treatment system consisting of a nanostructured titania interlayer loaded with an inhibitor and a hybrid silicate film deposited on the TiO₂ layer is shown to provide protection against active corrosion of mild steel. A nanostructured TiO₂ interlayer was prepared on the mild steel surface via controllable hydrolysis of titanium alkoxide. To further improve this pre-treatment, the hybrid silicate film was synthesized from tetraethylorthosilicate and 3-glycidoxypropyltrimethoxysilane precursors. The morphology and structure of the titania interlayer and hybrid silicate film were characterized with atomic force microscopy, scanning electron microscopy and energy dispersive X-ray spectroscopy techniques. The corrosion performance of the coatings was examined using electrochemical techniques, including potentiodynamic scanning and electrochemical impedance spectroscopy. The TiO₂ nanostructure calcinated/inhibitor/hybrid silicate system shows enhanced corrosion performance, as confirmed by impedance and polarization measurements.     

Study of the influence of Nb content and sintering temperature on TiO2 sensing films

Nb-doped TiO₂ nanopowders have been synthesized with a wide range of Nb contents (0-10 at.%) and of calcination temperatures (600-900 °C). The materials have been structurally characterized by means of X-ray diffraction, Raman spectroscopy and transmission electron microscopy. The niobium introduction retards the anatase-to-rutile transformation and hinders grain growth mechanisms. The electrical behavior studied for CO and ethanol gases showed that the response to ethanol is slightly diminished by the incorporation of Nb atoms and not affected by the structure modification. However, the response to CO is modified by structure changes such as the anatase/rutile transformation, grain size and Nb segregation. For the samples treated at 700 °C, the best response to CO is achieved for 4 at.% of Nb.     

脉冲啁啾对干涉相关测宽的影响及其消除方法

本文深入讨论了脉冲啁啾的非线性起源及其对干涉相关测宽(等值宽度和条纹计数)法的影响。提出根据干涉相关曲线下包络最大值位置适当降低等值宽度位置和用计算机平均处理干涉相关信息的技术以消除啁啾的影响。     

Effect of ZnO doping on morphology and electrochemical properties of sub-micron RuO2 sensing electrode of DO sensor

Thick-film 20 mol% ZnO-doped RuO₂ sensing electrodes (SEs) were fabricated by screen-printing technique on the platinised alumina substrate of the planar electrochemical dissolved oxygen (DO) sensor. The effect of ZnO doping on morphology, electrochemical properties and sensing characteristics of the sensor was investigated. It was found that ZnO doping has not only improved the SE structure, but has also enhanced selectivity of the DO sensor. Selectivity testing exhibited that the presence of Cl⁻, Li⁺, SO₄²⁻, NO³⁻, Ca²⁺, PO₄³⁻, Mg²⁺, Na⁺ and K⁺ with a concentration range of 10⁻⁷ to 10⁻¹ mol/L in the solution had practically no effect on the sensor's emf. The reason in enhancement of the sensor characteristics could be related to the establishment of the better structured SE as more advanced crystallization is achieved for the doped RuO₂-SE.     

Effect of fabrication method on the structure and properties of a nanostructured nickel-free stainless steel

An ASTM F2581 nanostructured stainless steel was fabricated by two different powder metallurgy routes; Hot Powder Forging (HPF) and Binder Assisted Extrusion (BAE) methods. Their structure and mechanical properties were investigated and compared. In both fabrication methods, the alloy powder was made by using main alloying elements through mechanical alloying, along with the addition of a sintering aid. In the BAE method, a paste was prepared by mixing alloy powders with polymer followed by cold extrusion, polymer removal, and sintering. In the HPF method, the alloy powders were hot forged under high pressure. The structure and the size of the austenite crystallite of the samples were investigated by scanning electron microscopy (SEM), FE-SEM, x-ray diffraction (XRD) and transmission electron microscopy (TEM). It was determined that the samples prepared by the HPF method are generally denser than those made via BAE. The porosities are smaller and almost uniform in size and morphology in the HPF method. Furthermore, microhardness and tensile tests were performed on the samples. The results show that the ductility of BAE samples is higher than the HPF samples. The fracture surface of the BAE sample has deeper dimples, indicating higher ductility for BAE samples. On the other hand, both the hardness and strength of HPF samples are higher than those of the BAE samples. The results show that both methods produced specimens with considerably higher strength and hardness than conventional 316L stainless steel.     

Effect of iron catalyst on the microstructure and electrochemical properties of vanadium carbide-derived carbons

Carbide-derived carbons (CDCs) are obtained from vanadium carbide powders in the presence or absence of iron catalyst at chlorination temperatures of 400, 600, 800 and 1000 °C. The structural differences of the resulting carbons are characterized by low-temperature nitrogen sorption, Raman spectroscopy, X-ray diffraction, and transmission electron microscope techniques. Unlike monotonous increase in the degree of order for the CDC synthesized without addition of iron catalyst, a various decrease for the CDC synthesized with the catalyst is observed. This difference is due to the formation of many nano-diamonds during the CDC processing in the presence of iron catalyst. Variation in the specific surface area is associated with the degree of order in the CDC. CDC synthesized with iron catalyst at chlorination temperature of 800 °C shows the highest specific surface area, as well as the best electrochemical performance.