A novel ZIF-8@ZIF-67/Au core–shell metal organic framework nanocomposite as a highly sensitive electrochemical sensor for nitrite determination

An ultrasensitive electrochemical sensor for the simultaneous detection of baicalin and baicalein in pharmaceuticals and serum samples

Developing an accurate and ultrasensitive method for the simultaneous detection of baicalin and baicalein, two key flavonoid from Scutellaria baicalensis, is critical, particularly in the context of traditional Chinese medicine. This study focuses on an innovative electrochemical approach, utilizing a biochar (BC)/ZIF-67/MnCo2O4 composite, which was fabricated via a combination of ultrasonic, calcination, and hydrothermal treatments. The resulting BC/ZIF-67/MnCo2O4 electrode exhibits exceptional sensitivity, with linear response ranges of 0.01 μM-400 μM. The limits of detection (LOD) for baicalein and baicalin were as low as 0.056 nM and 0.49 nM, respectively. The practical evaluations in serum and Scutellaria baicalensis demonstrate high recovery rates of 93.65 %-95.25 % for baicalein and 98.23 %-101.52 % for baicalin, with relative standard deviations below 3.99 % and 2.92 %, respectively. This study not only presents a promising technique for quality control in traditional Chinese medicine but also expands the potential applications of BC/ZIF-67/MnCo2O4 composites in electrochemical sensing, paving the way for applications in food safety monitoring and herbal medicine standardization.

A high-performance electrochemical sensor based on dendritic Au/Zn modified carbon cloth for the determination of nitrite in aquaculture

Nitrite is a common nitrogen-containing compound that possesses high biological toxicity, thereby posing a serious threat to aquatic organisms. Therefore, it is imperative to develop a rapid and quantitative determination approach for nitrite. In this study, the aim was to prepare a novel electrochemical sensor to determine nitrite. This was achieved by synthesizing Au/Zn dendritic complexes on a carbon cloth self-supported electrode after plasma treated by a stepwise strategy of electrodeposition and in-situ corrosion. In accordance with the optimal experimental conditions, the electrode exhibited remarkable catalytic activity for the electrooxidation of nitrite ions (pH = 8.0), accompanied by a considerable enhancement in peak anodic current in comparison to the unmodified electrode. The sensor exhibited a wide linear range (1-833 μM, 833-8330 μM), high sensitivity (3506 μA mM-1 cm-2, 538 μA mM-1 cm-2), a low detection limit (0.43 μM), and excellent selectivity, reproducibility, and stability for the determination of nitrite. Furthermore, the prepared sensor was successfully applied to the detection of nitrite in tap water, fish holding pond water and duck pond water, demonstrating good recovery and no significant difference from the spectrophotometric results. The results suggest that the electrochemical sensor developed in this study represents a straightforward yet efficacious approach to the development of advanced portable sensors for aquaculture applications.

2D MXene-Based Nanoscale Materials for Electrochemical Sensing Toward the Detection of Hazardous Pollutants: A Perspective

MXenes (Mn+1XnTx), a subgroup of 2-dimensional (2D) materials, specifically comprise transition metal carbides, nitrides, and carbonitrides. They exhibit exceptional electrocatalytic and photocatalytic properties, making them well-suited for the detection and removal of pollutants from aqueous environments. Because of their high surface area and remarkable properties, they are being utilized in various applications, including catalysis, sensing, and adsorption, to combat pollution and mitigate its adverse effects. Different characterization techniques like XRD, SEM, TEM, UV-Visible spectroscopy, and Raman spectroscopy have been used for the structural elucidation of 2D MXene. Current responses against applied potential were measured during the electrochemical sensing of the hazardous pollutants in an aqueous system using a variety of electroanalytical techniques, including differential pulse voltammetry, amperometry, square wave anodic stripping voltammetry, etc. In this review, a comprehensive discussion on structural patterns, synthesis, properties of MXene and their application for electrochemical detection of lethal pollutants like hydroquionone, phenol, catechol, mercury and lead, etc. are presented. This review will be helpful to critically understand the methods of synthesis and application of MXenes for the removal of environmental pollutants.

Fabrication of Highly Sensitive and Selective Nitrite Colorimetric Sensor Based on the Enhanced Peroxidase Mimetic Activity of Using Acetic Acid Capped Zinc Oxide Nanosheets

Nitrite ions (NO2-), as one of the leading type-A inorganic-anion, showing significant-effects in the aquatic environment and also to humans health. Whereas, the higher uptake causes detrimental threat to human health leading to various chronic diseases, thus demanding efficient, reliable and convenient method for its monitoring. For this purpose, in the present research study we have fabricated the mimetic nonozyme like catalyst based colorimetric nitrite sensor. The acetic acid capped Zinc Oxide (ZnO) nanosheets (NSs) were introduce as per-oxidase mimetic like catalyst which shows high efficiency towards the oxidative catalysis of colorless tetramethylbenzidine (TMB) to oxidized-TMB (blue color) in the presence of Hydrogen-peroxide (H2O2). The present nitrite ions will stimulate the as formed oxidized-TMB (TMBox), and will caused diazotization reaction (diazotized-TMBox), which will not only decreases the peak intensity of UV-visible peak of TMBox at 652 nm but will also produces another peak at 446 nm called as diazotized-TMBox peak, proving the catalytic reaction between the nitrite ions and TMBox. Further, the prepared colorimetric sensor exhibits better sensitivity with a wider range of concentration (1 × 10-3-4.50 × 10-1 µM), lowest limit of detection (LOD) of 0.22 ± 0.05 nM and small limit of quantification (LOQ) 0.78 ± 0.05 nM having R2 value of 0.998. Further, the colorimetric sensor also manifest strong selectivity towards NO2- as compared to other interference in drinking water system. Resultantly, the prepared sensor with outstanding repeatability, stability, reproducibility, re-usability and its practicability in real water samples also exploit its diverse applications in food safety supervision and environmental monitoring.

3D porous conductive matrix based on phase-transited BSA and covalent coupling-stabilized transition ZnS-CNT for antifouling and on-site detection of nitrite in soil

Nitrite plays a critical role in a variety of nitrification and denitrification processes in the nitrogen cycle. Due to the high surface energy, tendency to aggregate, and poor conductivity, current nitrite ZnS-based sensing platform could not meet the need of on-site nitrite detection in smart agriculture. In order to address these issues, the carboxylated carbon nanotube (CNT) was introduced to reduce the surface energy and prevented aggregation of ZnS, while ZnS-carboxylated CNT (ZnS-CNT) composite also provided excellent electrochemical conductivity. Furthermore, the introduction of phase transition BSA (PTB) created a three-dimensional porous conductive matrix without interfering with the mass transfer process of nitrite. The resulting sensing platform exhibited a linear detection range of 10 nM to 0.4 mM for nitrite, with a detection limit of 0.73 nM. And this sensing platform had the excellent antifouling ability to direct detection nitrite in real soil suspension. In addition, the sensing platform demonstrated remarkable resistance to interferences from pH variations, microbial presence, and organic pollutants that usually present in soil environment. Therefore, on-site detection of nitrite ions in soil environment was realized no needing complex pretreatments.

Portable wireless electrochemical sensing of breviscapine using core-shell ZIFs-derived Co nanoparticles embedded in N-doped carbon nanotube polyhedra-modified electrode

A core-shell ZIF-67@ZIF-8-derived Co nanoparticles embedded in N-doped carbon nanotube polyhedra (Co/C-NCNP) hybrid nanostructure was prepared by a pyrolysis method. The synthesized Co/C-NCNP was modified on the screen-printed carbon electrode and used for the portable wireless sensitive determination of breviscapine (BVC) by differential pulse voltammetry. The Co/C-NCNP had a large surface area and excellent catalytic activity with increasing Co sites to combine with BVC for selective determination, which led to the improvement of the sensitivity of the electrochemical sensor. Under optimized conditions, the constructed sensor had linear ranges from 0.15 to 20.0 µmol/L and 20.0 to 100.0 µmol/L with the limit of detection of 0.014 µmol/L (3S0/S). The sensor was successfully applied to BVC tablet sample analysis with satisfactory results. This work provided the potential applications of zeolitic imidazolate framework-derived nanomaterials in the fabrication of electrochemical sensors for the sensitive detection of drug samples.

Tunable growth of a single high-density ZIF nanoshell on a gold nanoparticle isolated in an optical trap

Here, we demonstrate an all-optical method using an optical tweezer to controllably grow high quality zeolitic imidazolate framework (ZIF) nanoshells on the surface of gold nanoparticles (AuNPs) and monitor the growth via darkfield spectroscopy. Our single particle approach allows us to localize an individual NP within a microscope slide chamber containing ZIF precursors at the focus of an optical microscope and initiate growth through localized heating without affecting the bulk system. Darkfield spectroscopy is used to characterize changes to the localized surface plasmon resonance (LSPR) of the AuNP resulting from refractive index changes as the ZIF crystal grows on the surface. We show that the procedure can be generalized to grow various types of ZIF crystals, such as ZIF-8, ZIF-11, and a previously undocumented ZIF variety. Utilizing both computational models and experimental methods, we identify the thickness of ZIF layers to be self-limiting to ∼50 nm or less, depending on the trapping laser power. Critically, the refractive index of the shells here was found to be above 1.6, indicating the formation of high-density crystals, previously accessible only through slow atomic layer deposition and not through a bulk heating process. The single particle method developed here opens the door for bottom-up controllable growth of custom nanostructures with tunable optical properties.

Introducing Mn into ZIF-8 nanozyme for enhancing its catalytic activities and adding specific recognizer for detection of organophosphorus pesticides

In order to design and establish a highly efficient and selective nanozyme-based sensing platform for the UV-vis detection of organophosphorus pesticides (OPs), Mn was introduced into ZIF-8 nanozyme for enhancing its catalytic activities and adding specific recognizer. The Mn-doped ZIF-8 (Mn-ZIF-8) nanocomposites were synthesized with a very facile one-pot method by heating the mixture of ZnO, 2-methylimidazole (Hmin) and Mn(CH3COO)2·4H2O in a solvent-free system at 180 °C for 8 h. The Mn-ZIF-8 nanocomposite showed a higher peroxidase activity and an additional thiocholine (TCh)-degradable property compared to the pristine ZIF-8. OPs could inhibit acetylcholinesterase (AChE) to catalyze the hydrolysis of acetylthiocholine (ATCh) to produce TCh, thus blocking the degradation of Mn-ZIF-8 and protecting the catalysis of the oxidation of colorless 3,3',5,5'-tetramethylbenzydine (TMB) to blue oxidized TMB (ox-TMB). Accordingly, a detection method for OPs with high sensitivity and selectivity was designed and established on the basis of the Mn-ZIF-8 nanozyme with a linear range of 0.1-20 nM and a limit of detection (LOD) as low as 54 pM.

Electrochemical sensors based on platinum-coated MOF-derived nickel-/N-doped carbon nanotubes (Pt/Ni/NCNTs) for sensitive nitrite detection

As excess nitrite has a serious threat to the human health and environment, constructing novel electrochemical sensors for sensitive nitrite detection is of great importance. In this report, platinum nanoparticles were deposited on nickel-/N-doped carbon nanotubes, which were obtained through a self-catalytically grown process with Ni-MOF as precursors. The as-prepared Pt/Ni/NCNTs were applied as amperometric sensors and presented superior sensing properties for nitrite detection. Benefiting from the synergy of Pt and Ni/NCNTs, Pt/Ni/NCNTs displayed much wider detection ranges (0.5-40 mM and 40-110 mM) for nitrite sensing. The sensitivity is 276.92 μA mM^-1 cm^-2 and 224.39 μA mM^-1 cm^-2, respectively. The detection limit is 0.17 μM. The Pt/Ni/NCNTs sensors also showed good feasibility for nitrite sensing in real samples (milk and peach juice) analysis. The active Pt/Ni/NCNTs composites and facile fabrication technique may provide useful strategies to develop other sensitive nitrite sensors.

Polyaniline-Supported Nickel Oxide Flower for Efficient Nitrite Electrochemical Detection in Water

A modified electrode with conducting polymer (Polyaniline) and NiO nanoflowers was prepared to detect nitrite ions in drinking water. A simple method was used to prepare the NiO nanoflower (NiOnF). Several techniques characterized the as-prepared NiOnF to determine the chemical structure and surface morphology of the NiO, such as XRD, XPS, FT-IR, and TGA. The activity of the electrode toward nitrite sensing was investigated over a wide range of pH (i.e., 2 to 10). The amperometry method was used to determine the linear detection range and limit. Accordingly, the modified electrode GC/PANI/NiOnf showed a linear range of detection at 0.1-1 µM and 1-500 µM. At the same time, the limit of detection (LOD) was 9.7 and 64 nM for low and high concentrations, respectively. Furthermore, the kinetic characteristics of nitrite, such as diffusion and transport coefficients, were investigated in various media. Moreover, the charge transfer resistance was utilized for nitrite electrooxidation in different pH values by the electrochemical impedance technique (EIS). The anti-interfering criteria of the modified surfaces were utilized in the existence of many interfering cations in water (e.g., K⁺, Na⁺, Cu²⁺, Zn²⁺, Ba²⁺, Ca²⁺, Cr²⁺, Cd²⁺, Pd²⁺). A real sample of the Nile River was spiked with nitrite to study the activity of the electrode in a real case sample (response time ~4 s). The interaction between nitrite ions and NiO{100} surface was studied using DFT calculations as a function of adsorption energy.

Bionic Enzyme-Assisted Ion-Selective Amperometric Biosensor Based on 3D Porous Conductive Matrix for Point-of-Care Nitrite Testing

Nitrite plays a critical role in a variety of physiological processes and maintaining the nitrite level in an appropriate range is vital to keep healthy. Current nitrite analysis methods lack sensitivity and require tedious operations, which could not meet the need of point-of-care (POC) nitrite detection in precision medicine. Here we present a cyanocobalamin (VB₁₂) bionic enzyme-assisted ion-selective amperometric biosensor based on 3D porous conductive matrix (PCM), which can facilitate rapid and accurate POC nitrite monitoring in complex biofluids. The experimental findings quantitatively demonstrate that the biosensor has a sensitivity of 64.08 μA/(mM·cm²), a wide linear range of 0.025-45 mM, and low limit of detection of 1 nM. Moreover, the developed VB₁₂/BSA-PCM biosensor shows outstanding stability after 21 days with 2% decline in current signal, and high repeatability between batches with RSD of only 1.29%. Real salivary nitrite detection has been evaluated, and the results match well with the commercial nitrite analyzer. Thus, the bionic enzyme-assisted ion-selective amperometric biosensor proposed herein has potential utility as an affordable tool for POC detection and home-based healthcare.

Gold Nanomaterials and their Composites as Electrochemical Sensing Platforms for Nitrite Detection

Nitrite is one of the abundant toxic components existing in the environment and is likely to have a great potential to affect human health badly. For that reason, it has become crucial to build a reliable nitrite detection method. In recent years, several nitrite monitoring systems have been proposed. Compared with traditional analytical strategies, the electrochemical approach has a bunch of advantages, including low cost, rapid response, easy operation, simplicity, etc. In this case, noble metal nanomaterials, especially Au-based nanomaterials, have attracted attention in electrode modification because of higher catalytic activity, facile mass transfer, and broad active area for determining nitrite. This review is based on the state-of-the-art, which includes a variety of nanomaterials that have been coupled with AuNPs for the creation of nanocomposites, and the construction as well as development of electrochemical sensors for nitrite detection over the last few years (2016-2022). A background study on synthesizing different morphological AuNPs and nanocomposites has also been introduced. The fabrication methods and sensing capabilities of modified electrodes are given special consideration.