Simultaneous determination of naphthol isomers at poly(3-methylthiophene)-nano-Au modified electrode with the enhancement of surfactant

A novel covalent triazine framework developed for efficient determination of 1-naphthol in water

Covalent triazine frameworks (CTFs) are an exciting new class of porous organic materials with excellent chemical stability and easy functionalization. In recent years, CTFs have gained increasing attention in electrochemical detection of environmental contaminants. Herein, a novel CTF material was successfully synthesized by the solvothermal condensation of 1,3,5-tris-(4-aminophenyl)triazine (TAPT) and 2,3,6,7-tetrabromonapthalene dianhydride (TBNDA) for determination of 1-naphthol in water. The obtained CTF, denoted here as TATB, comprised uniformly sized spherical particles (diameter 0.5-2 μm) with a highly conjugated structure that benefited electron transfer processes when applied to a glassy carbon electrode (GCE). A TATB/GCE working electrode showed excellent catalytic activity for the oxidation of 1-naphthol, with the oxidation peak current being directly proportional to the 1-naphthol concentration in the range of 0.01-10.0 μM, with a detection limit of 5.0 nM (S/N = 3). In addition, the TATB/GCE sensor possesses excellent reproducibility, sensitivity, and selectivity for 1-naphthol determination in aqueous solution. This work highlights the potential of CTFs in electrochemical sensing, whilst also demonstrating a sensitive and stable sensor platform for 1-naphthol detection in water.

Electrochemical sensing for naphthol isomers based on the in situ growth of zeolitic imidazole framework-67 on ultrathin CoAl layered double hydroxide nanosheets by a reaction-diffusion technique

It is established that ultrathin layered double hydroxide nanosheets (LDHNS) and zeolitic imidazole frameworks (ZIF) are desirable electrochemical sensing modifiers owing to their large surface area and abundant catalytic sites. Integration of them is thus an effective solution to maximize their electrocatalytic activity. Herein, a novel reaction-diffusion framework (RDF) technique is applied for the in situ growth of ZIF-67 on ultrathin CoAl-LDHNS (CoAl-LDHNS@ZIF-67). In a confined space of the agar gel matrix of RDF, the coordination reaction between organic ligands and CoAl-LDHNS without an additional Co²⁺ source achieves the controllable growth of ZIF-67 crystals through a long vertical diffusion. The prepared composite comprises both CoAl-LDHNS and ZIF-67 components with a certain ratio and provides a large surface area and amply catalytic sites, thus realizing a rapid transfer of electron and mass. The CoAl-LDHNS@ZIF-67 modified electrode is employed for the simultaneous detection of naphthol isomers by differential pulse voltammetry. Naphthol isomers display anodic reactions with a wide peak potential difference, allowing their simultaneous detection feasible. Voltammetric responses of α-naphthol and β-naphthol follow good linearity against the concentration in a wide range from 0.3 to 150 μM with limits of detection of 54 and 82 nM, respectively. The proposed sensor also demonstrates excellent selectivity, stability, reproducibility, and practicability for the simultaneous detection of naphthol isomers.

A novel electrochemical paper sensor for low-cost detection of 5-methyltetrahydrofolate in egg yolk

An electrochemical deposition method was used to fabricate a gold nanoflower (AuNF) and carbon nanoparticle (CNP) modified carbon paper (CP) sensor (AuNFs-CNPs/CP) for the low-cost detection of 5-methyltetrahydrofolate (5-mTHF) in egg yolk. AuNF morphology and structures were characterized by scanning electron microscopy (SEM) and X-ray photoelectron spectroscopy (XPS), revealing nanoflower sizes in the 50 to 200 nm range. AuNFs formed on the sensor were in the Au⁰. We evaluated 5-mTHF assay performance using cyclic voltammetry, differential pulse voltammetry and chronoamperometry. The AuNFs-CNPs/CP sensor detected 5-mTHF concentrations in the ranges from 1 to 5 mg L^-1 and 1-20 μg L^-1, with an excellent limit of detection of 1 μg L^-1 and good selectivity toward 5-mTHF, when compared to other potentially interfering molecules in samples. The AuNFs-CNPs/CP sensor was also used to detect 5-mTHF in folate-rich, and was found to be twice than that of ordinary egg yolk.

Electrochemical sensing platform for naphthol isomers based on in situ growth of ZIF-8 on reduced graphene oxide by a reaction-diffusion technique

Enhancing the dispersibility and conductivity is an effective solution to develop the application zeolitic imidazole frameworks (ZIF) in the electrochemical field. This work thus employs a novel reaction-diffusion framework (RDF) technique for the in situ growth of ZIF-8 crystals on graphene oxide (GO@ZIF-8) matrixes. In detail, the outer electrolyte of 2-methyl imidazole naturally diffuses into the inner agar gel matrix containing Zn²⁺ cations and GO nanosheets. The long reaction-diffusion makes the growth of ZIF-8 crystals controllable in a vertical gradient. After thermal treatment, the title product of ZIF-8 in situ grown on reduced graphene oxide (rGO@ZIF-8) is obtained and thus exhibits good dispersibility, high conductivity, large surface area, and more catalytic sites. The glassy carbon electrode (GCE) was modified by casting the rGO@ZIF-8 suspension. The obtained rGO@ZIF-8/GCE displays excellent catalytic activity toward naphthol (NAP) isomers. Under the optimal conditions, the amperometric currents of 1-NAP and 2-NAP demonstrate the good linear relationship in wide ranges of 0.05-12 μM and 0.02-15 μM, respectively. Their limits of detection are as low as 15 and 17 nM, respectively. The fabricated modified electrode exhibits excellent selectivity, stability, and reproducibility. The sensor is also utilized to detect NAP molecules in real water samples and indicates good accuracy and reliability.

Recent Developments in Polymer Nanocomposite-Based Electrochemical Sensors for Detecting Environmental Pollutants

The human population is generally subjected to diverse pollutants and contaminants in the environment like those in the air, soil, foodstuffs, and drinking water. Therefore, the development of novel purification techniques and efficient detection devices for pollutants is an important challenge. To date, experts in the field have designed distinctive analytical procedures for the detection of pollutants including gas chromatography/mass spectrometry and atomic absorption spectroscopy. While the mentioned procedures enjoy high sensitivity, they suffer from being laborious, expensive, require advanced skills for operation, and are inconvenient to deploy as a result of their massive size. Therefore, in response to the above-mentioned limitations, electrochemical sensors are being developed that enjoy robustness, selectivity, sensitivity, and real-time measurements. Considerable advancements in nanomaterials-based electrochemical sensor platforms have helped to generate new technologies to ensure environmental and human safety. Recently, investigators have expanded considerable effort to utilize polymer nanocomposites for building the electrochemical sensors in view of their promising features such as very good electrocatalytic activities, higher electrical conductivity, and effective surface area in comparison to the traditional polymers. Herein, the first section of this review briefly discusses the most important methods for polymer nanocomposites synthesis, such as in situ polymerization, direct mixing of polymer and nanofillers (melt-mixing and solution-mixing), sol-gel, and electrochemical methods. It then summarizes the current utilization of polymer nanocomposites for the preparation of electrochemical sensors as a novel approach for monitoring and detecting environmental pollutants which include heavy metal ions, pesticides, phenolic compounds, nitroaromatic compounds, nitrite, and hydrazine in different mediums. Finally, the current challenges and future directions for the polymer nanocomposites-based electrochemical sensing of environmental pollutants are outlined.

Ordered Mesoporous NiCo2O4 Nanospheres as a Novel Electrocatalyst Platform for 1-Naphthol and 2-Naphthol Individual Sensing Application

The novel ordered mesoporous NiCo₂O₄ (meso-NiCo₂O₄) nanospheres were synthesized by the nanocasting strategy followed by a calcination process for 2-naphthol (2-NAP) and 1-naphthol (1-NAP) individual sensing application. The as-obtained meso-NiCo₂O₄ material possesses mesoporous structure in spinel crystalline type with a larger specific surface area than other structures. The meso-NiCo₂O₄-modified carbon paste electrode exhibited excellent electrocatalytic performance for NAP detection by amperometry measurement. The fabricated sensor of 2-NAP and 1-NAP has a wide linear detection range (0.02-300 and 0.02-20 μM) with high sensitivity (1.822 and 1.510 μA μM^-1 cm^-2) and low limit of detection (0.007 and 0.007 μM), respectively. In addition, the NAP sensors possess excellent reproducibility, stability, and selectivity.

Sensitive electrochemical determination of rifampicin using gold nanoparticles/poly-melamine nanocomposite

Green and facile method for fabrication of a conductive polymer–Au nanocomposite platform as a novel electrochemical sensing layer for rifampicin.