Novel multi walled carbon nanotubes/β-cyclodextrin based carbon paste electrode for flow injection potentiometric determination of piroxicam

Fabrication of nitrogen-carbon mediated γ-Mo2N nanocomposite based electrochemical sensor for rapid and sensitive determination of antioxidant 6-PPD in the environment

The rapid and sensitive determination of antioxidant N-(1,3-dimethylbutyl)-N'-phenyl-p-henylenediamine (6-PPD) in the environment is crucial for early intervention to prevent its adverse effects. Here, a reliable electrochemical sensor based on a N-C mediated γ-Mo2N nanocomposite (γ-Mo2N@N-C) modified carbon paste electrode (CPE) was developed and applied for selective and sensitive determination of 6-PPD. Benefiting from the superior stability and faster electron diffusion coefficient, the peak current responded to 6-PPD on the sensor linearly over a concentration range from 5 × 10-8 mol L-1 to 1.0 × 10-5 mol L-1 with a detection limit of 1.67 × 10-8 mol L-1 (4.48 ng mL-1). Moreover, the sensor maintained good anti-interference ability in the determination of 6-PPD in soil samples from different regions in Zhengzhou City. Furthermore, the density functional theory (DFT) calculations combined with kinetics analysis proved that the enhanced basicity of the γ-Mo2N@N-C facilitated the deprotonation of 6-PPD, with the preferred orientation facet of (200) in γ-Mo2N playing a vital role in inducing the dissociation of 6-PPD, thereby improving the sensor's response. Such an electrochemical sensor, with its good stability and superior sensitivity, has the potential to be applied for real-time evaluation and monitoring of environmental pollutants.

Metal-organic frameworks (MOFs) composite of polyaniline-CNT@aluminum succinate for non-enzymatic nitrite sensor

Nitrite has been linked to a variety of health issues, as well as cancer and oxygen deficiency when its allowable limit is exceeded. Nitrite monitoring and detection are required due to the negative effects on public health. Metal-organic frameworks (MOFs)-based nanomaterials/composites have recently been shown to have the potential for various biological and medical applications like sensing, imaging, and drug delivery. As a result, this research creates an efficient electrochemical sensor by incorporating MOFs into polyaniline (PANI)/carbon nanotube (CNT) cast on the GCE. In situ oxidative polymerization was used to construct an aluminum succinate MOF (Al-Succin)-incorporated CNT/PANI nanocomposite (PANI/CNT@Al-Succin) and well characterized by various characterization techniques, namely, field emission scanning electron microscopy (FE-SEM), Fourier transform infrared spectroscopy (FT-IR), X-ray diffraction spectroscopy (XRD), X-ray photoelectron spectroscopy (XPS), thermogravimetric-differential thermal analysis (TGA-DTA), cyclic voltammetry (CV), and four probes to measure DC electrical conductivity. Cyclic voltammetry and linear sweep voltammetry techniques were employed to detect nitrite on the surface of PANI/CNT@Al-Succin-modified glassy carbon electrode (GCE). PANI/CNT@Al-Succin-modified GCE demonstrated good current response and electrocatalytic property towards nitrite compared to bare GCE. The newly synthesized electrode exhibited a high electrocatalytic activity towards nitrite oxidation and showed a linear response ranging from 5.7 to 74.1 μM for CV and 8.55-92.62 μM for LSV. The obtained LOD values for CV (1.16 μM) and LSV (0.08 μM) were significantly below the WHO-defined acceptable nitrite limit in drinking water. Results of recovery studies for real samples of apple juice, orange juice, and bottled water were 98.92%, 99.38%, and 99.90%, respectively. These values show practical usability of PANI/CNT@Al-Succin in real samples.

Hybrid Plasticizers Enhance Specificity and Sensitivity of an Electrochemical-Based Sensor for Cadmium Detection

In addition to their use as an additive to improve physical properties of solvent polymeric membranes, plasticizers have a considerable impact on the specificity and sensitivity of membrane-modified electrochemical sensors. In this work, we aim at the hybridization of two different plasticizers using the electropolymerization technique in the development of a cadmium(II)-selective electrochemical sensor based on screen-printed gold electrode along with cyclic voltammetric measurement. At this point, we first screen for the primary plasticizer yielding the highest signal using cyclic voltammetry followed by pairing it with the secondary plasticizers giving rise to the most sensitive current response. The results show that the hybridization of DOS and TOTM with 3:1 weight ratio (~137.7-μm-thick membrane) renders a signal that is >26% higher than that from the sensor plasticized by DOS per se in water. The solution of 0.1 mM hydrochloric acid (pH 4) is the optimal supporting electrolyte. In addition, hybrid plasticizers have adequate redox capacity to induce cadmium(II) transfer from bulk solution to the membrane/water interfaces. Conversion of voltammetric signals to semi-integral currents results in linearity with cadmium(II) concentration, indicating the irreversible cadmium(II) transfer to the membrane. The DOS:TOTM hybrid sensor also exhibits high sensitivity, with a limit of detection (LOD) and limit of quantitation (LOQ) of 95 ppb and 288 ppb, respectively, as well as greater specificity towards cadmium(II) than that obtained from the single plasticizer sensor. Furthermore, recovery rates of spiked cadmium(II) in water samples were higher than 97% using the hybrid plasticizer sensor. Unprecedentedly, our work reports that the hybridization of plasticizers serves as ion-to-electron transducer that can improve the sensor performance in cadmium(II) detection.

Piroxicam

A comprehensive profile of piroxicam including the nomenclatures, formulae, elemental composition, appearance, uses and applications. The methods which were utilized for the preparation of the drug substance and their respective schemes are outlined. The physical characteristics of the drug including the ionization constant, solubility, x-ray powder diffraction pattern, differential scanning calorimetry, thermal behavior and spectroscopic studies are described. The methods which were used for the analysis of the drug substance in bulk drug and/or in pharmaceutical formulations including the compendial, spectrophotometric, electrochemical and the chromatographic methods are reported. The stability, toxicity, pharmacokinetics, bioavailability, drug evaluation, comparison, in addition to compiled reviews on the drug substance are involved. Finally, more than four hundred and fifty references are listed at the end of this profile.

Dopamine-functionalized cyclodextrins: modification of reduced graphene oxide based electrodes and sensing of folic acid in human serum

A mandatory step in any sensor fabrication is the introduction of analyte-specific recognition elements to the transducer surface. In this study, the possibility to anchor β-cyclodextrin-modified dopamine to a reduced graphene oxide based electrochemical transducer for the sensitive and selective sensing of folic acid is demonstrated. The sensor displays good electrocatalytic activity toward the oxidation of folic acid. The strong affinity of the surface-confined β-cyclodextrin for folic acid, together with favorable electron transfer characteristics, resulted in a sensor with a detection limit of 1 nM for folic acid and a linear response up to 10 μM. Testing of the sensor on serum samples from healthy individuals and patients diagnosed with folic acid deficiency validated the sensing capability. Graphical abstract.

Electrochemical Determination of Rivastigmine Hydrogen Tartrate at β-Cyclodextrin/Multi-Walled Carbon Nanotubes Modified Electrode

Background:

Electrochemical techniques can easily be adopted to solve many problems of pharmaceutical interest. The implementation of electroanalytical methods in the assay of pharmaceutical formulations has increased greatly. Nowadays, owing to the critical importance of electron transfer and surface properties, chemically modified electrodes have been employed in electrochemical sensors. The chemically modified electrode is one of the most popular electroanalytical sensors and used in several applications.

Methods:

In this work, a β-cyclodextrine/multi-walled carbon nanotubes (β-CD/MWCNTs) composite modified glassy carbon electrode (GCE) was produced and applied to the detection of Rivastigmine hydrogen tartrate (RVT) in pharmaceutical formulations. The voltammetric feature of RVT at this β- CD/MWCNTs modified electrode was evaluated using cyclic voltammetry and square wave voltammetry.

Results:

The β-cyclodextrin and multi-walled carbon nanotubes modified glassy carbon electrode displayed good electrocatalytic activity in the oxidation of rivastigmine hydrogen tartrate with relatively high sensitivity, stability and lifetime. The calibration graph of the analyte was linear over the range 10- 1500 µM with two linear segments and the detection limit was obtained as 2.0 µM (S/N=3). The results showed that the electrochemical sensor has good sensitivity and selectivity.

Conclusion:

The β-CD/MWCNTs modified electrode displayed a high electrochemical activity and good sensitivity toward the oxidation of RVT. Compared with the bare MWCNTs coated sensor, the response of analyte increased soundly and the response potential of target analyte shifted negatively. The results indicated that the β-CD/MWCNTs film coated electrode had good catalysis to the voltammetric oxidation of RVT. The prepared sensor was applied to determine RVT in pharmaceutical samples with satisfactory yields. The outcomes indicate that β-CD/MWCNTs coated electrode is a safe choice for the detection of RVT.

Recent developments in the synthesis and applications of graphene-family materials functionalized with cyclodextrins

The introduction of cyclodextrin species to graphene-family materials (GFMs) constitutes an important area of research, especially in terms of the development of applied nanoscience. The chemistry of cyclodextrins is the so-called host-guest chemistry, which has impacted on many fields of research, including catalysis, electrochemistry and nanomedicine. Cyclodextrins are water-soluble and biocompatible supramolecules, and therefore they may introduce new interesting properties to GFMs and may enhance the physicochemical/biological features of native GFMs. The reported methods for the conjugation of cyclodextrins to GFMs utilize either covalent or non-covalent approaches. The recent progress in the applications of GFMs functionalized with cyclodextrins, with the respect to the chemistry and features of these conjugates, is discussed. Special consideration is also given to the recent developments in (i) nanomedicine, (ii) electrochemistry, (iii) adsorption and (iv) catalysis. Examples of these materials are discussed in this work, together with the future outlook on the impact of GFM-cyclodextrin conjugates in the development of applied nanoscience.

Real time monitoring of the curing degree and the manufacturing process of fiber reinforced composites with a carbon nanotube buckypaper sensor

This paper proposes a flexible and highly sensitive carbon nanotube buckypaper as a sensing layer embedded within a composite for cure monitoring applications. The buckypaper was fabricated with mono-dispersion of multi-wall carbon nanotubes by a spray-vacuum filtration method. Six different curing conditions (with maximum heating temperatures of 120 °C, 108 °C, 95 °C, 90 °C, 85 °C and 75 °C) were designed to characterize and analyze the electromechanical response of the BP sensor to the composite structure, and the results indicated that the temperature coefficient of resistance of buckypaper is associated to the resin curing behavior. The critical value (−7.18 × 10⁻⁴ °C⁻¹) of the temperature coefficient of resistance was determined. Experimental results also show that a stable three-dimensional network of resin molecular chains is formed and that the polymer presents a glassy state when the value of the temperature coefficient of resistance is greater than the critical value. Based on this relationship, a hypothesis was raised that for the complete curing of the resin, the temperature coefficient of resistance of the buckypaper sensor should meet the critical value condition, which was also consistent with the differential scanning calorimetry testing of the curing degree. The buckypaper sensor was found to be sensitive to the curing degree of the resin, and has a promising future in applications in composite manufacturing processes. Moreover, the properties of composite components are indeed able to be improved via the monitoring and optimization of the curing parameters.

A flexible and highly sensitive carbon nanotube buckypaper (BP) as a sensing layer was embedded within composite for cure monitoring applications. BP sensor can monitor the resin phase transition and resin cure degree during composite manufacturing.

Manganese dioxide nanoparticles incorporated within ionic liquid derived fibrillated mesoporous carbon: electrode material for high-performance supercapacitors

This article is the first example of the incorporation of metal oxide nanoparticles within ionic liquid derived nano-fibrillated mesoporous carbon (IFMC), as electrode materials for supercapacitor applications.

Novel screen printed potentiometric sensors for the determination of oxicams

Screen printed sensors based on carbon nanotubes/β-cyclodextrin nanocomposite was applied for potentiometric determination of oxicam derivatives. Sensors showed improved potential stability and lifetime detection limit of 6 × 10⁻⁷ mol L⁻¹.

Biosensor based on multi-walled carbon nanotubes paste electrode modified with laccase for pirimicarb pesticide quantification

This study focused on the development of a sensitive enzymatic biosensor for the determination of pirimicarb pesticide based on the immobilization of laccase on composite carbon paste electrodes. Multi-walled carbon nanotubes (MWCNTs) paste electrode modified by dispersion of laccase (3%, w/w) within the optimum composite matrix (60:40%, w/w, MWCNTs and paraffin binder) showed the best performance, with excellent electron transfer kinetic and catalytic effects related to the redox process of the substrate 4-aminophenol. No metal or anti-interference membrane was added. Based on the inhibition of laccase activity, pirimicarb can be determined in the range 9.90 × 10(-7) to 1.15 × 10(-5) mol L(-1) using 4-aminophenol as substrate at the optimum pH of 5.0, with acceptable repeatability and reproducibility (relative standard deviations lower than 5%). The limit of detection obtained was 1.8 × 10(-7) mol L(-1) (0.04 mg kg(-1) on a fresh weight vegetable basis). The high activity and catalytic properties of the laccase-based biosensor are retained during ca. one month. The optimized electroanalytical protocol coupled to the QuEChERS methodology were applied to tomato and lettuce samples spiked at three levels; recoveries ranging from 91.0 ± 0.1% to 101.0 ± 0.3% were attained. No significant effects in the pirimicarb electroanalysis were observed by the presence of pro-vitamin A, vitamins B1 and C, and glucose in the vegetable extracts. The proposed biosensor-based pesticide residue methodology fulfills all requisites to be used in implementation of food safety programs.