Electrochemical oxidation behavior of nitrite on a chitosan-carboxylated multiwall carbon nanotube modified electrode

Development of electrochemical sensors for quick detection of environmental (soil and water) NPK ions

All over the world, technology is becoming more and more prevalent in agriculture. Different types of instruments are already being used in this sector. For the time being, every farmer is trying to produce more crops on a piece of land. Eventually, soil loses its nutrients; however, to grow more crops, farmers use more fertilizers without knowing the proper conditions of the soil in real time. To overcome this issue, many scientists have recently focused on developing electrochemical sensors to detect macronutrients, i.e., nitrogen (N), phosphorus (P), and potassium (K), in soil or water rapidly. In this review, we focus mainly on the recent developments in electrochemical sensors used for the detection of nutrients (NPK) in different types of samples. As it is outlined, the use of smart and portable electrochemical sensors can be helpful for the reduction of excess fertilizer and can play a vital role in maintaining suitable conditions in soils and water. We are optimistic that this review can guide researchers in the development of a portable and suitable NPK detection system for soil nutrients.

Nitrites Detection with Sensors Processed via Matrix-Assisted Pulsed Laser Evaporation

This work is focused on the application of a laser-based technique, i.e., matrix-assisted pulsed laser evaporation (MAPLE) for the development of electrochemical sensors aimed at the detection of nitrites in water. Commercial carbon-based screen-printed electrodes were modified by MAPLE via the application of a newly developed composite coating with different concentrations of carbon nanotubes (CNTs), chitosan, and iron (II) phthalocyanine (C₃₂H₁₆FeN₈). The performance of the newly fabricated composite coatings was evaluated both by investigating the morphology and surface chemistry of the coating, and by determining the electro-catalytic oxidation properties of nitrite with bare and modified commercial carbon-based screen-printed electrode. It was found that the combined effect of CNTs with chitosan and C₃₂H₁₆FeN₈ significantly improves the electrochemical response towards the oxidation of nitrite. In addition, the MAPLE modified screen-printed electrodes have a limit of detection of 0.12 µM, which make them extremely useful for the detection of nitrite traces.

Magnetic nanomaterials based electrochemical (bio)sensors for food analysis

It is widely accepted that nanotechnology attracted more interest because of various values that nanomaterial applications offers in different fields. Recently, researchers have proposed nanomaterials based electrochemical sensors and biosensors as one of the potent alternatives or supplementary analytical tools to the conventional detection procedures that consumes a lot of time. Among different nanomaterials, researchers largely considered magnetic nanomaterials (MNMs) for developing and fabricating the electrochemical (bio)sensors for numerous utilizations. Among several factors, healthier and higher quality foods are the most important preferences of consumers and manufacturers. For this reason, developing new techniques for rapid, precise as well as sensitive determination of components or contaminants of foods is very important. Therefore, developing the new electrochemical (bio)sensors in food analysis is one of the key and effervescent research fields. In this review, firstly, we presented the properties and synthesis strategies of MNMs. Then, we summarized some of the recently developed MNMs-based electrochemical (bio)sensors for food analysis including detecting the antioxidants, synthetic food colorants, pesticides, heavy metal ions, antibiotics and other analytes (bisphenol A, nitrite and aflatoxins) from 2010 to 2020. Finally, the present review described advantages, challenges as well as future directions in this field.

Voltammetric sensor based on long alkyl chain tetraalkylammonium ionic liquids comprising ascorbate anion for determination of nitrite

An electrochemical sensor was fabricated utilizing ionic liquids possessing cations with long alkyl chains such as trimethyl octadecylammonium and behenyl trimethylammonium and ascorbate anion. The ionic liquids were drop-coated onto the electrode. Thin modifying layers were prepared. Cyclic voltammetric investigations revealed electrostatic interactions between the electrochemical probes and the modified surface, proving that a positive charge was established at the film surface. Hence, negatively charged species such as nitrite can be pre-concentrated on the surface of presented modified electrodes. The fabricated electrodes have been used as a voltammetric sensor for nitrite. Due to the electrostatic accumulation properties of long alkyl cation, the assay exhibits a remarkable improvement in the voltammetric response toward nitrite oxidation. The influence of pH on the electrode response was thoroughly investigated, and the mechanism of the electrode was established. The developed sensor showed a linear electrochemical response in the range 1.0–50 μM with a detection limit of 0.1 μM. The electrode revealed good storage stability, reproducibility, and anti-interference ability. The determination of nitrite performed in curing salts brought satisfactory results.

CdS/TiO2 Nanocomposite-Based Photoelectrochemical Sensor for a Sensitive Determination of Nitrite in Principle of Etching Reaction

The CdS/TiO₂ nanocomposite (NC) photoelectrochemical (PEC) sensor was constructed based on a new sensing strategy for nitrite assay. The CdS etching process caused by nitrite-in-acid solution was confirmed and applied to nitrite sensing. The CdS etching phenomenon occurring on the sensor led to an obvious reduction in the photocurrent response under visible-light irradiation, which responded to the nitrite concentration. The CdS/TiO₂ NC-based PEC sensor exhibited excellent performance on nitrite detection. The linear range for nitrite determination was from 1-100 and 100-500 μM, and the sensitivity of the PEC sensor was 2.91 and 0.186 μA μM^-1 cm^-2, respectively. The detection limit of the sensor was 0.56 μM (S/N = 3). In addition, the PEC sensor was also equipped with advantages such as good selectivity, excellent stability, low background, and recyclability. Satisfying results were obtained for the nitrite assay in real samples by such a PEC sensor. In summary, this work contributed a fresh idea to precisely determinate nitrite through PEC sensing.

Polymers and Plastics Modified Electrodes for Biosensors: A Review

Polymer materials offer several advantages as supports of biosensing platforms in terms of flexibility, weight, conformability, portability, cost, disposability and scope for integration. The present study reviews the field of electrochemical biosensors fabricated on modified plastics and polymers, focusing the attention, in the first part, on modified conducting polymers to improve sensitivity, selectivity, biocompatibility and mechanical properties, whereas the second part is dedicated to modified "environmentally friendly" polymers to improve the electrical properties. These ecofriendly polymers are divided into three main classes: bioplastics made from natural sources, biodegradable plastics made from traditional petrochemicals and eco/recycled plastics, which are made from recycled plastic materials rather than from raw petrochemicals. Finally, flexible and wearable lab-on-a-chip (LOC) biosensing devices, based on plastic supports, are also discussed. This review is timely due to the significant advances achieved over the last few years in the area of electrochemical biosensors based on modified polymers and aims to direct the readers to emerging trends in this field.

Heterostructural CuO-ZnO Nanocomposites: A Highly Selective Chemical and Electrochemical NO2 Sensor

A simple one-step chemical method is employed for the successful synthesis of CuO(50%)-ZnO(50%) nanocomposites (NCs) and investigation of their gas sensing properties. The X-ray diffraction studies revealed that these CuO-ZnO NCs display a hexagonal wurtzite-type crystal structure. The average width of 50-100 nm and length of 200-600 nm of the NCs were confirmed by transmission electron microscopic images, and the 1:1 proportion of Cu and Zn composition was confirmed by energy-dispersive spectra, i.e., CuO(50%)-ZnO(50%) NC studies. The CuO(50%)-ZnO(50%) NCs exhibit superior gas sensing performance with outstanding selectivity toward NO2 gas at a working temperature of 200 °C. Moreover, these NCs were used for the indirect evaluation of NO2 via electrochemical detection of NO2 - (as NO2 converts into NO2 - once it reacts with moisture, resulting into acid rain, i.e., indirect evaluation of NO2). As compared with other known modified electrodes, CuO(50%)-ZnO(50%) NCs show an apparent oxidation of NO2 - with a larger peak current for a wider linear range of nitrite concentration from 20 to 100 mM. We thus demonstrate that the as-synthesized CuO(50%)-ZnO(50%) NCs act as a promising low-cost NO2 sensor and further confirm their potential toward tunable gas sensors (electrochemical and solid state) (Scheme 1).

Carbon Nanotubes with Carbon Blacks as Cofillers to Improve Conductivity and Stability

In this study, a simple solution-mixing method is used to develop a kind of excellent flexible, electrically conductive adhesives (ECAs). Carbon nanotubes (CNTs) and carbon blacks (CBs) as cofillers were added into Ag-based pastes. The use of the two fillers is due to the consideration that these two materials may provide positive synergistic effects for improving the conductivity of ECAs. The conductivity, flexibility, cyclability, and oxidation resistance of ECAs with different contents of carbon fillers were studied. It was found that a small amount of CNTs or CBs can dramatically improve the ECAs' conductivity. Solution-mixing method brings excellent carbon nanofiller dispersion in polymer matrix. Highly dispersed CNTs and CBs among the Ag flakes formed three-dimensional conducting networks to improve the conductivity of ECAs. The conductivity of ternary hybrid ECAs (with addition of 3 wt % CNTs and 2 wt % CBs) with a low content of 55 wt % Ag flakes is higher than that of the ECAs filled with only the Ag content over 65 wt %. Meanwhile, by selecting thermoplastic polyurethane resin as the matrix, the ECAs exhibited excellent mechanical compliance. The resistivity did not change when the ECAs were bended at a 60% flexural strain or pressed under 1200 kPa. Additionally, the adhesion strength of the new composited ECAs is better than that of a commercial ECA (Abletherm 3188). Further, no obvious conductivity change was observed when the sample was stored in ambient air condition at 80 °C and 60% relative humidity (60%) for 15 days.

Effect of metal in Schiff bases of chitosan adsorbed on glassy carbon electrode in the inhibition of sphingomyelinase C toxin

This study was conducted to assess the catalytic electrode surface adsorption and capture properties of different metal chitosan derivatives in aqueous phosphate buffer solution (pH = 7.3). Early, recent work showed that the response of Iron chitosan complex with R = -CH₃ on the periphery, over blood red cells in presence of sphingomyelinase C was protected. The effect of others substituent (R = -Br, -Cl, -F, NO₂, -OCH₃, -H) on the periphery of the Schiff base ligand did not show correlation with the oxidation of sphingomyelinase C and its biological response. For this reason, various adsorbed metal (M = Fe of recent work, Cu, Ni and Co) complexes of chitosan and Schiff bases on glassy carbon electrode for the oxidation of sphingomyelinase C were investigated and compared, each one with -CH₃ group on the periphery of the Schiff base. UV-Vis and IR-TF spectroscopies, electrochemistry and microscopy assay were performed; then, the metal effect underlying. For the Schiff base, cobalt and copper complexes did not proved to be a remarkable cellular protector in presence of the enzyme, but the nickel complex showed to be a cellular protector at short time, this conclusion help to proposal a reaction mechanism for the electrochemical and biological studies.

Methods for the detection and determination of nitrite and nitrate: A review

Various techniques for the determination of nitrite and/or nitrate developed during the past 15 years were reviewed in this article. 169 references were covered. The detection principles and analytical parameters such as matrix, detection limits and detection range of each method were tabulated. The advantages and disadvantages of various methods were evaluated. In comparison to other methods, spectrofluorimetric methods have become more attractive due to its facility availability, high sensitivity and selectivity, low limits of detection and low-cost.

S. B. An electrochemical sensing platform for trace recognition and detection of an anti-prostate cancer drug flutamide in biological samples

Systematic illustration of electrode fabrication.

Mechanistic characterization and inhibition of sphingomyelinase C over substituted Iron Schiff bases of chitosan adsorbed on glassy carbon electrode

The medical treatment of laxoscelisms is based solely on supportive measures. Although equine antiserum for Sphingomyelinase C (SMASE) and D isomers are available, it is not used due to the risk of an anaphylactic reaction and its unproven efficacy. As potential enzyme inhibitors, derivatives of Iron chitosan complexes were studied (Shiff base having -R = -H, -Cl, -Br, -F, -OCH₃, -CH₃, -NO₂). These chitosan complexes were chosen because they have revealed good results in medicine and catalysis due to their biodegradable characteristics and bioavailability. Besides considering that these complexes have not been studied in relation to this toxin. The mechanisms underlying the catalytic and catcher effects of Iron chitosan complexes were studied using electrochemistry, UV-Vis spectroscopy and microscopic assay at physiological pH. The electrochemical studies showed that one of seven Schiff bases of chitosan adsorbed on glassy carbon electrode was electrocatalytically active for the oxidation of sphingomyelinase at 1.27 V, and that allowed proposing a reaction scheme for SMASE oxidation by adsorbed Iron complexes. On the other hand, even though the spectroscopic studies indicated that there was no chemical bond formation between the complex and SMASE in solution, the microscopic studies showed that this complex proved to be a remarkable cellular protector in presence of the enzyme. In conclusion, Shiff base of chitosan with R = -CH₃ was the only active complex in front of sphingomyelinase C, protecting red blood cells, according to our electrochemical and microscopic studies.

Hydrothermal preparation of reduced graphene oxide-silver nanocomposite using Plectranthus amboinicus leaf extract and its electrochemical performance

Graphene based nanocomposites are receiving increasing attention in many fields such as material chemistry, environmental science and pharmaceutical science. In this study, a facial synthesis of a reduced graphene oxide-silver nanocomposite (RGO-Ag) was carried out from Plectranthus amboinicus leaf extract. The synthesized nanocomposite was characterized by using X-ray diffraction, scanning electron microscope, Fourier transform infrared spectroscopy, X-ray photoelectron spectroscopy, transmission electron microscope and UV-vis spectroscopy for structural confirmation. The reduction of graphene oxide and silver ions was achieved simultaneously due to the reducibility of the Plectranthus amboinicus leaf extract. We further investigated the electrochemical properties of the biosynthesized RGO-Ag nanocomposite. A nonenzymatic H₂O₂ electrochemical sensor was shown to be successfully fabricated by using biosynthesized RGO-Ag nanocomposite. Moreover, the fabricated electrochemical sensor also showed good selectivity.

Preparation of hexagonal BN whiskers synthesized at low temperature and their application in fabricating an electrochemical nitrite sensor

Hexagonal boron nitride (h-BN) whiskers were synthesized via the polymeric precursor method using boric acid (H₃BO₃) and melamine (C₃H₆N₆) as raw materials at 1073–1273 K in flowing nitrogen/hydrogen (5% hydrogen).

Novel electrochemical preparation of gold nanoparticles decorated on a reduced graphene oxide–fullerene composite for the highly sensitive electrochemical detection of nitrite

In this study, we report a novel amperometric nitrite sensor based on a glassy carbon electrode (GCE) modified with gold nanoparticles (AuNP) decorated reduced graphene oxide–fullerene (RGO–C60) composite.

Significant improvements in the mechanical properties of chitosan functionalized carbon nanotubes/epoxy composites

TEM image of the fracture structure of CNTs/CS/EP.

Hydrophobicity effects in iron polypyridyl complex electrocatalysis within Nafion thin-film electrodes

Four polypyridyl redox catalysts Fe(bp)₃²⁺, Fe(ph)₃²⁺, Fe(dm)₃²⁺, and Fe(tm)₃²⁺ (with bp, ph, dm, and tm representing 2,2′-bipyridine, 1,10-phenanthroline, 4,4′-dimethyl-2,2′-bipyridine, and 3,4,7,8-tetramethyl-1,10-phenanthroline, respectively) are investigated for the electrocatalytic oxidation of three analytes (nitrite, arsenite, and isoniazid).

Nitrite Oxidation with Copper-Cobalt Nanoparticles on Carbon Nanotubes Doped Conducting Polymer PEDOT Composite

Copper-cobalt bimetal nanoparticles (Cu-Co) have been electrochemically prepared on glassy carbon electrodes (GCEs), which were electrodeposited with conducting polymer nanocomposites of poly(3,4-ethylenedioxythiophene) (PEDOT) doped with carbon nanotubes (CNTs). Owing to their good conductivity, high mechanical strength, and large surface area, the PEDOT/CNTs composites offered excellent substrates for the electrochemical deposition of Cu-Co nanoparticles. As a result of their nanostructure and the synergic effect between Cu and Co, the Cu-Co/PEDOT/CNTs composites exhibited significantly enhanced catalytic activity towards the electrochemical oxidation of nitrite. Under optimized conditions, the nanocomposite-modified electrodes had a fast response time within 2 s and a linear range from 0.5 to 430 μm for the detection of nitrite, with a detection limit of 60 nm. Moreover, the Cu-Co/PEDOT/CNTs composites were highly stable, and the prepared nitrite sensors could retain more than 96 % of their initial response after 30 days.

Polymer/carbon nanotubes coated graphite surfaces for highly sensitive nitrite detection

This study describes the preparation of poly(vinylferrocenium)/multi-walled carbon nanotubes (PVF(+)/MWCNTs) coated electrode and its use for sensitive electrochemical nitrite detection. PVF(+)/MWCNTs composite coated disposable pencil graphite electrode (PVF(+)/MWCNTs/PGE) was prepared by electropolymerization of poly(vinylferrocene) (PVF) in the presence of MWCNTs with one-step electropolymerization. Characterization of PVF(+)/MWCNTs/PGE was carried out with scanning electron microscopy (SEM), cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS). Then electrochemical detection of nitrite was performed using differential pulse voltammetry (DPV). Nanocomposite coated electrode showed high sensitivity to nitrite with a detection limit of 0.1 μM. The electrode platform was successfully applied to a commercial mineral water sample.

Kinetics and functional effectiveness of nisin loaded antimicrobial packaging film based on chitosan/poly(vinyl alcohol)

The aim of this study was to evaluate the kinetics and functional effectiveness of Nisin loaded chitosan/poly(vinyl alcohol) (Nisin-CS/PVA) as an antibacterial packaging film. The films were prepared by coating method and Staphylococcus aureus (S. aureus, ATCC6538) was used as test bacterium. The intermolecular hydrogen bonds between CS and PVA molecules were confirmed. The elasticity of films was significantly improved by the incorporation of PVA, and the film could also bear a relative high tensile strength at 26.7 MPa for CS/PVA=1/1. As CS/PVA ratio decreased, the water vapor permeability (WVP) decreased and reached its minimum value 0.983 × 10(-10)gm(-1)s(-1) at CS/PVA=1/1, meanwhile, oxygen permeability (OP) increased but still lower than 0.91 cm(3) μm m(-2)d(-1)kPa(-1) for CS/PVA=1/1 as the CS/PVA ratio was above 1:1. The initial diffusion of nisin (Mt/M ∞ < 2/3) from CS/PVA film could be well described by the Fickian diffusion equation. Owing to the positively charged nisin at pH below isoelectric point (pI, 8.8) and its increasing dissolubility in water as the pH reduced, the diffusion of nisin from the films strongly depended on pH and ionic strength besides CS/PVA ratio and temperature. Moreover, the thermodynamic parameters suggested the spontaneous and endothermic diffusion of nisin from the films. The resulting data can provide some valuable information for the design of film in structure and ingredient.

Cobalt phthalocyanine tetracarboxylic acid modified reduced graphene oxide: a sensitive matrix for the electrocatalytic detection of peroxynitrite and hydrogen peroxide

The electrocatalytic properties of cobalt phthalocyanine modified reduced graphene oxide for peroxynitrite and hydrogen peroxide are investigated.