Voltammetric determination of nitrite by using a multiwalled carbon nanotube paste electrode modified with chitosan-functionalized silver nanoparticles

Zirconium Phosphate-Incorporated Polyaniline-Graphene Oxide Composite Modified Electrodes for Effective and Selective Detection of Nitrite

Nitrite contamination in food, water, and environmental samples poses a substantial health hazard, owing to its capacity for transformation into carcinogenic compounds. Given the profound ecological and physiological implications, precise and highly sensitive surveillance of nitrite has emerged as an imperative area of concern, addressing the substantial detrimental impact that it can have on both terrestrial and aquatic ecosystems. The novel electroactive polyaniline-graphene oxide composite, incorporating hexagonal zirconium phosphate discs (PGZrP), was systematically engineered as a foundation for an advanced electrochemical sensor, enabling precise nitrite detection in diverse aqueous and biological matrices. At a specific potential peak of +0.85 V, observed within a pH 7.0 phosphate buffer solution, the PGZrP-modified glassy carbon electrode (GCE) exhibited exceptional electrocatalytic proficiency in the sensing nitrite ions (NO2-), surpassing the performance of alternative electrode configurations, including the zirconium phosphate-modified GCE (ZrP/GCE), graphene oxide-modified GCE (GO/GCE), polyaniline-graphene oxide-modified GCE (PG/GCE), and the unmodified bare glassy carbon electrode. The constructed sensor demonstrated an impressive limit of detection at 80 nM along with a broad and linear detection range spanning from 124 nM to 40 mM. The synergistic effect created by the close contact between ZrP and PG, which resulted in a well-enhanced electrochemical sensing capability, was responsible for this exceptional activity. The developed sensor exhibited an enhanced electrochemical performance characterized by an extended operational range, a heightened detection threshold, and exceptional sensitivity. The PGZrP/GCE sensor, as fabricated, consistently demonstrated commendable operational stability, robust reproducibility, and remarkable repeatability in its capacity for nitrite detection. Furthermore, its successful application in the precise quantification of nitrite levels within environmental water samples and blood specimens showcased an impressive recovery rate, establishing it as a promising tool for diverse analytical applications. These findings indicate the promising potential of the PGZrP composite for integration into electrochemical devices designed to deliver rapid response times, heightened sensitivity, and sustained stability, thereby placing it as a potential candidate for the production of cutting-edge sensors, particularly those employed for the precise recognition of nitrite in aquatic and biological specimens.

The Role of Silver Nanoparticles in Electrochemical Sensors for Aquatic Environmental Analysis

With rapidly increasing environmental pollution, there is an urgent need for the development of fast, low-cost, and effective sensing devices for the detection of various organic and inorganic substances. Silver nanoparticles (AgNPs) are well known for their superior optoelectronic and physicochemical properties, and have, therefore, attracted a great deal of interest in the sensor arena. The introduction of AgNPs onto the surface of two-dimensional (2D) structures, incorporation into conductive polymers, or within three-dimensional (3D) nanohybrid architectures is a common strategy to fabricate novel platforms with improved chemical and physical properties for analyte sensing. In the first section of this review, the main wet chemical reduction approaches for the successful synthesis of functional AgNPs for electrochemical sensing applications are discussed. Then, a brief section on the sensing principles of voltammetric and amperometric sensors is given. The current utilization of silver nanoparticles and silver-based composite nanomaterials for the fabrication of voltammetric and amperometric sensors as novel platforms for the detection of environmental pollutants in water matrices is summarized. Finally, the current challenges and future directions for the nanosilver-based electrochemical sensing of environmental pollutants are outlined.

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.

SiO2/Al2O3/C grafted 3-n propylpyridinium silsesquioxane chloride-based non-enzymatic electrochemical sensor for determination of carcinogenic nitrite in food products

The excessive uptake of nitrite is perilous and detrimental for human health that prone to cancer disease. Herein, described the synthesis of SiO₂/Al₂O₃/C material through the sol-gel procedure followed by grafting with 3-n propylpyridinium silsesquioxane chloride organic ligand for enhancing electrochemical activity. H-NMR, ¹³C NMR, and ²⁹Si studies were performed for confirmation of surface functionalization through the grafting technique. The surface morphology was evaluated through SEM and TEM techniques. The material showed an irregular and flakes-like structure that exhibited more compactness and conglomerate structure with no segregation in phase was observed after grafting. The elemental composition was confirmed from EDX analysis. The electrochemical measurements were performed with cyclic voltammetry, electrochemical impedance spectroscopy (EIS), and chronoamperometry. The prepared hybrid inorganic-organic composite Si/C/Al/SiPy⁺Cl^- was applied for the modification of the glassy carbon (GC) electrode and assessed as a sensor for nitrite determination. The sensor showed the low limit of detection (0.01 μM), low limit of quantification (0.08 μM), wide linear response range (0.2-280 μM), and high sensitivity (410 μA·μM^-1). It gave a quick response time of <1 s in the presence of 70 μM nitrite. The fabricated sensor showed high sensitivity, chemical stability, and insignificant interference from co-existing species present in sausage meat and food industry discharges. The repeatability of the sensor was evaluated as 2.5 % R.S.D.; for n = 10 at 50 μM nitrite.

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.

A novel electrochemical platform based on mesoporous silica/titania and gold nanoparticles for simultaneous determination of norepinephrine and dopamine

An amorphous and mesoporous silica/titania (SiTi) material was synthesized by sol-gel method and its surface was modified with gold nanoparticles (AuNP) previously stabilized in a chitosan solution. The presence of small AuNP, with diameter lower than 10 nm was confirmed by transmission electron microscopy (TEM) and UV-Vis spectroscopy. Carbon paste electrodes were prepared to test the electrochemical properties by using cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS) in [Fe(CN)₆]^3-/4- solution probe whereby the material silica-titania/gold nanoparticles (SiTi/AuNP) showed a huge improvement in the redox peak current and low charge transfer resistance. This electrode presented a good response for both norepinephrine and dopamine by means of square wave voltammetry (SWV) measurements; great sensitivity for both analytes, in an extensive linear range, was obtained. The limits of detection were 0.35 μmol L^-1 and 0.57 μmol L^-1 for norepinephrine and dopamine, respectively. Additionally, this electrode showed high selectivity for both analytes and it was applied in the simultaneous determination of norepinephrine and dopamine. The sensor was also tested in simulated biological fluids presenting a good recovery. The SWV electrochemical response of norepinephrine was also investigated in the presence of possible interferers such as uric acid, ascorbic acid and glucose and there was no significant interference. The prepared electrode also exhibits good reproducibility for norepinephrine detection, with relative standard deviation of 5.19%.

Graphene oxide quantum dots immobilized on mesoporous silica: preparation, characterization and electroanalytical application

Because of its high surface area and combination of various functional groups, graphene oxide (GO) is currently one of the most actively studied materials for electroanalytical applications. It is not practical to utilize self-supported GO on its own and thus it is commonly integrated with different supporting carriers. Having a large lateral size, GO can only wrap the particles of the support and thus can significantly reduce the surface area of porous materials. To achieve synergy from the high surface area and polyfunctional nature of GO, and the rigid structure of a porous support, the lateral size of GO must essentially be decreased. Recently reported graphene oxide quantum dots (GOQDs) can fulfil this task. Here we report the successful preparation of an SiO₂-GOQDs hybrid, where GOQDs have been incorporated into the mesoporous network of silica. The SiO₂-GOQDs emit a strong luminescence with a band maximum at 404 nm. The Raman spectrum of SiO₂-GOQDs shows two distinct peaks at 1585 cm⁻¹ (G-peak) and 1372 cm⁻¹ (D-peak), indicating the presence of a graphene ordered basal plane with aromatic sp²-domains and a disordered oxygen-containing structure. Covalent immobilization of GOQDs onto aminosilica via such randomly structured oxygen fragments was proven with the help of Fourier transform infrared spectroscopy, solid-state cross-polarization magic angle spinning ¹³C nuclear magnetic resonance, and X-ray photoelectron spectroscopy. SiO₂-GOQDs were used as a modifier of a carbon paste electrode for differential pulse voltammetry determination of two antibiotics (sulfamethoxazole and trimethoprim) and two endocrine disruptors (diethylstilbestrol (DES) and estriol (EST)). The modified electrodes demonstrated a significant signal enhancement for EST (370%) and DES (760%), which was explained by a π–π stacking interaction between GOQDs and the aromatic system of the analytes.

Graphene oxide quantum dots incorporated into a mesoporous silica network have been used as a modifier of a carbon paste electrode for the determination of antibiotics and hormones.

Developments and applications of nanomaterial-based carbon paste electrodes

This review summarizes the progress that has been made in the past ten years in the field of electrochemical sensing using nanomaterial-based carbon paste electrodes. Following an introduction into the field, a first large section covers sensors for biological species and pharmaceutical compounds (with subsections on sensors for antioxidants, catecholamines and amino acids). The next section covers sensors for environmental pollutants (with subsections on sensors for pesticides and heavy metal ions). Several tables are presented that give an overview on the wealth of methods (differential pulse voltammetry, square wave voltammetry, amperometry, etc.) and different nanomaterials available. A concluding section summarizes the status, addresses future challenges, and gives an outlook on potential trends.