rGO/ZnO/Nafion nanocomposite as highly sensitive and selective amperometric sensor for detecting nitrite ions (NO2−)

Efficient nitrite determination by electrochemical approach in liquid phase with ultrasonically prepared gold-nanoparticle-conjugated conducting polymer nanocomposites

An electrochemical nitrite sensor probe is introduced herein using a modified flat glassy carbon electrode (GCE) and SrTiO3 material doped with spherical-shaped gold nanoparticles (Au-NPs) and polypyrrole carbon (PPyC) at a pH of 7.0 in a phosphate buffer solution. The nanocomposites (NCs) containing Au-NPs, PPyC, and SrTiO3 were synthesized by ultrasonication, and their properties were thoroughly characterized through structural, elemental, optical, and morphological analyses with various conventional spectroscopic methods, such as field-emission scanning electron microscopy, energy-dispersive X-ray spectroscopy, high-resolution transmission electron microscopy, powder X-ray diffraction, X-ray photoelectron spectroscopy, and Brunauer-Emmett-Teller method. The peak currents due to nitrite oxidation were characterized in detail and analyzed using conventional cyclic voltammetry (CV) as well as differential pulse voltammetry (DPV) under ambient conditions. The sensor response increased significantly from 0.15 to 1.5 mM of nitrite ions, and the sensor was fabricated by coating a conducting agent (PEDOT:PSS) on the GCE to obtain the Au-NPs/PPyC/SrTiO3 NCs/PEDOT:PSS/GCE probe. The sensor's sensitivity was determined as 0.5 μA/μM∙cm2 from the ratio of the slope of the linear detection range by considering the active surface area (0.0316 cm2) of the flat GCE. In addition, the limit of detection was determined as 20.00 ± 1.00 µM, which was found to be satisfactory. The sensor's stability, pH optimization, and reliability were also evaluated in these analyses. Overall, the sensor results were found to be satisfactory. Real environmental samples were then analyzed to evaluate the sensor's reliability through DPV, and the results showed that the proposed novel electrochemical sensor holds great promise for mitigating water contamination in the real samples with the lab-made Au-NPs/PPyC/SrTiO3 NC. Thus, this study provides valuable insights for improving sensors for broad environmental monitoring applications using the electrochemical approach.

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.

Reduced graphene oxide/zinc oxide composite as an electrochemical sensor for acetylcholine detection

Acetylcholine (ACh) plays a pivotal role as a neurotransmitter, influencing nerve cell communication and overall nervous system health. Imbalances in ACh levels are linked to neurodegenerative diseases, such as Alzheimer's and Parkinson's. This study focused on developing electrochemical sensors for ACh detection, utilizing graphene oxide (GO) and a composite of reduced graphene oxide and zinc oxide (rGO/ZnO). The synthesis involved modified Hummers' and hydrothermal methods, unveiling the formation of rGO through deoxygenation and the integration of nano-sized ZnO particles onto rGO, as demonstrated by XPS and TEM. EIS analysis also revealed the enhancement of electron transfer efficiency in rGO/ZnO. Cyclic voltammograms of the electrode, comprising the rGO/ZnO composite in ACh solutions, demonstrated prominent oxidation and reduction reactions. Notably, the composite exhibited promise for ACh detection due to its sensitivity, low detection threshold, reusability, and selectivity against interfering compounds, specifically glutamate and gamma-aminobutyric acid. The unique properties of rGO, such as high specific surface area and electron mobility, coupled with ZnO's stability and catalytic efficiency, contributed to the composite's potential in electrochemical sensor applications. This research, emphasizing the synthesis, fabrication, and characterization of the rGO/ZnO composite, established itself as a reliable platform for detecting the acetylcholine neurotransmitter.

An ultra-sensitive electrochemical sensing platform based on nanoflower-like Au/ZnO array on carbon cloth for the rapid detection of the nitrite residues in food samples

In this work, we constructed an enhanced electrochemical signal sensing platform using Au/ZnO nanoflake arrays coated on carbon cloth for the rapid detection of nitrite in food. Based on a stepwise synthesis strategy of electrodeposition and magnetron sputtering technique, AuNPs were sputtered onto ZnO nanoflower-like array sheets. Combining the high catalytic performance of AuNPs with the morphology of ZnO significantly increased the surface area and electrocatalytic activity of the electrodes. The prepared sensor showed a linear response range of 0.2-4986 μΜ, a limit of detection of 0.09 μM, and a high sensitivity of 5677 μA mM-1 cm-2. It is worth noting that the sensor can precisely detect nitrite in the presence of interfering substances and has excellent stability and reproducibility. In addition, the nitrite residues in several food samples were analyzed using this method and spectrophotometric method, and the results of the two methods were not significantly different.

Flower-like 3D MoS2 microsphere/2D C3N4 nanosheet composite for highly sensitive electrochemical sensing of nitrite

Nitrite pollution poses a serious threat to human health and the environment. In this study, a reliable and selective electrochemical (EC) sensor was developed for the quantitative determination of nitrite by combining flower-like three-dimensional (3D) MoS2 microspheres with two-dimensional (2D) C3N4 nanosheets. Benefiting from the synergistic effects of MoS2 and C3N4, the 3D MoS2/2D C3N4 nanocomposite displayed numerous active sites, a 3D mesoporous structure, high conductivity and excellent catalytic activity. The 3D MoS2/2D C3N4-modified glassy carbon electrode (GCE) exhibited a superior electrocatalytic activity toward nitrite oxidation, with a wider linear detection range (0.1-1100 μM), a lower detection limit (LOD) (0.065 μM, S/N = 3), outstanding stability, remarkable reproducibility and strong selectivity. Furthermore, the nitrite EC sensor was successfully applied to detect actual food and environmental samples involving sausage, pickled vegetables, river water and tap water, thus demonstrating the potential of the prepared 3D MoS2/2D C3N4/GCE for food analysis and environmental monitoring.

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.

Reduced graphene oxide-wrapped La0·8Sr0·2MnO3 microspheres sensing electrode for highly sensitive nitrite detection

An electrochemical nitrite sensor based on perovskite oxides La_0·8Sr_0·2MnO₃ (LSM) microspheres-decorated reduced graphene oxide (rGO) composite was presented to take the merit of the excellent electrocatalytic activity of the LSM and the large surface area of rGO. The content of rGO has been finely adjusted and the electrochemical sensor employing 15 wt% rGO has shown an ultralow nitrite detection limit of 0.016 μM and a high sensitivity of 0.041 μA μM^-1 cm^-2 and 0.039 μA μM^-1 cm^-2 in the range of 2-100 and 100-5000 μM, respectively. In addition, the proposed electrode shows good selectivity, reproducibility and stability, suitable for detection of nitrite at various pH values. The sensor was used to determine the nitrite level in environmental water samples with acceptable relative error, demonstrating its feasibility for practical environmental monitoring.

A novel electrochemical sensor based on nitrite-oxidizing bacteria for highly specific and sensitive detection of nitrites

Real-time nitrite control in water is necessary for environmental safety and human health, and has triggered the research and development of novel detection methods. Previous studies have made great progress on enzyme-free and enzyme electrochemical sensors. However, enzyme-free sensors have low selectivity and a complex preparation process, and enzyme sensors have short lifetimes, and these issues need to be addressed. In this work, we proposed for the first time a highly specific and sensitive biofilm sensor based on nitrite-oxidizing bacteria (NOB) for the bio-electrochemical detection of nitrite in water. The mechanism of nitrite detection was attributed to the competition of oxygen between aerobic respiration of the NOB and the cathode oxygen reduction on the carbon felt electrode, resulting in a decrease in current. This decrease in current (ΔI) had a linear relationship with the nitrite concentration in the range of 0.1 to 1 mg L^-1 and 1 to 10 mg L^-1, which was corresponding to the sensitivities of 48.62 and 2.24 μA mM^-1 cm^-2, respectively. And the limit of detection (LOD) was calculated to be 0.033 mg L^-1 (2.39 μM) with a signal-to-noise ratio of 3. Moreover, several common interfering ions had no effect on the nitrite detection owing to the functional microbial species (NOB) and weakly electrochemical behavior of electrode at the low potential of -0.1 V, showing high specificity for nitrite detection of biofilm sensor. Therefore, the actual nitrified wastewater was well detected by the biofilm sensor. In addition, allylthiourea (ATU) took good effect on the resistance of the influence of ammonia oxidizing bacteria (AOB) in the biofilm sensor, maintaining the high selectivity of biofilm sensor in case the biofilm sensor was fouled with AOB. The biofilm sensor in our work showed good selectivity, sensitivity and stability in long-term detection.

A high-sensitive and durable electrochemical sensor based on Geobacter-dominated biofilms for heavy metal toxicity detection

A highly sensitive electrochemical sensor for detecting low concentrations of heavy metals (Cd²⁺, Ni²⁺, Pb²⁺ and Cu²⁺) based on Geobacter-dominated biofilms was developed. The biosensor showed a high sensitivity for the determination of Cd²⁺ (109.7 μAμM^-1cm^-2) and the determination of Pb²⁺ (161.7 μAμM^-1cm^-2). The performance of three fitting models for biosensor response to heavy metal toxicity was investigated based on the relationship between total coulomb yield and heavy metal concentration. The full-area model (Equation a) provided the best fit, and the response times tended to be the fastest based on the peak current model (Equation c). Recovery methods were proposed to ensure the electrical activity of the biofilm for long-term monitoring. 16S rRNA gene sequence analysis showed that the most dominant genus in the anodic biofilm was Geobacter (44.1%-45.8%), indicating a stable community structure after continuous toxicity shock for 22 days. The confocal laser scanning microscope (CLSM) further proved the restorable and reusability of the biosensor. Thanks to the thin and electrically active Geobacter-dominated biofilms, it could be a good alternative biosensor for groundwater analysis etc. The results of this study contribute to the development of a highly sensitive and accurate biosensor with long-term usage towards on-site monitoring of heavy metals at low concentrations, improving the test performance of the biosensor for practical application.

Non-enzymatic nitrite amperometric sensor fabricated with near-spherical ZnO nanomaterial

A unique near-spherical ZnO nanostructure was synthesized by using mixed solvents composed of polyethylene glycol-400 (PEG-400) and water at the volume ratio of 12:1 via the solvo-thermal method, and it possessed an ideal morphology with higher uniformity, better dispersion and small particle size. Such ZnO was employed to modify glass carbon electrode (GCE) for the construction of electrochemical sensor, i.e. near-spherical ZnO/GCE, whose nitrite sensing performance was evaluated by Chronoamperometry (CA) and Linear Sweep Voltammetry (LSV). In order to emphasis the superior sensing property and extensive suitability for different electrochemical detection techniques, the excellent but not the same nitrite detection performance obtained from CA and LSV was individually given in detail. This sensor based on CA showed broad linearity range of 0.6 μM-0.22 mM and 0.46 mM-5.5 mM, improved sensitivity of 0.785 μA μM^-1 cm^-2 accompanied with low LOD of 0.39 μM. With regard to LSV, wide linearity response of 1.9 μM-0.8 mM and 1.08 mM-5.9 mM, high sensitivity of 0.646 μA μM^-1 cm^-2 with LOD of 0.89 μM were obtained. Meanwhile, this sensor displayed outstanding repeatability with RSD of 2.96% (n = 4), high reproducibility with low RSD (1.72%-2.35%, n = 4), strong selectivity towards nitrite with the concentration set at one-tenth of the interfering substances, ideal stability with the peak current intensity above 90% of its initial value after storage for one month and acceptable recovery of 1.72-2.35% to actual samples including ham sausage, pickle and tap water. The near-spherical ZnO nanomaterial may be a preferred candidate for the fabrication of nitrite electrochemical sensor, which may exhibit a fascinating application in terms of food analysis and environmental monitoring.

A Novel Highly Sensitive Electrochemical Nitrite Sensor Based on a AuNPs/CS/Ti3C2 Nanocomposite

Nitrite is common inorganic poison, which widely exists in various water bodies and seriously endangers human health. Therefore, it is very necessary to develop a fast and online method for the detection of nitrite. In this paper, we prepared an electrochemical sensor for highly sensitive and selective detection of nitrite, based on AuNPs/CS/MXene nanocomposite. The characterization of the nanocomposite was demonstrated by scanning electron microscopy (SEM), a transmission electron microscope (TEM), energy dispersive X-ray spectroscopy (EDX), X-ray diffraction (XRD), cyclic voltammetry (CV), and electrochemical impedance spectroscopy (EIS). Under the optimized conditions, the fabricated electrode showed good performance with the linear range of 0.5–335.5 μM and 335.5–3355 μM, the limit of detection is 69 nM, and the sensitivity is 517.8 and 403.2 μA mM⁻¹ cm⁻². The fabricated sensors also show good anti-interference ability, repeatability, and stability, and have the potential for application in real samples.