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.

Transport of hydrated nitrate and nitrite ions through graphene nanopores in aqueous medium.

Nitrate ( NO 3 - ) and nitrite ( NO 2 - ) ions are naturally occurring inorganic ions that are part of the nitrogen cycle. High doses of these ions in drinking water impose a potential risk to public health. In this work, molecular dynamics simulations are carried out to study the passage of nitrate and nitrite ions from water through graphene nanosheets (GNS) with hydrogen-functionalized narrow pores in presence of an external electric field. The passage of ions through the pores is investigated through calculations of ion flux, and the results are analyzed through calculations of various structural and thermodynamic properties such as the density of ions and water, ion-water radial distribution functions, two-dimensional density distribution functions, and the potentials of mean force of the ions. Current simulations show that the nitrite ions can pass more in numbers than the nitrate ions in a given time through GNS hydrogen-functionalized pore of different geometry. It is found that the nitrite ions can permeate faster than the nitrate ions despite the former having higher hydration energy in the bulk. This can be explained in terms of the competition between the number density of the ions along the pore axis and the free energy barrier calculated from the potential of mean force. Also, an externally applied electric field is found to be important for faster permeation of the nitrite over the nitrate ions. The current study suggests that graphene nanosheets with carefully created pores can be effective in achieving selective passage of ions from aqueous solutions.

Evaluation of human macrophage functional state by voltammetric monitoring of nitrite ions.

The method for assessing the level of nitric oxide (II) (NO) by voltammetric monitoring of nitrite ions was carried out on models M1 and M2 of polarized macrophages induced from monocytes of human peripheral blood with the addition of lipopolysaccharide (LPS) and interleukin-4 (IL-4), respectively. The model of induction of M1 and M2 macrophages was used in the work to achieve the corresponding shifts in the functional status of studied cells. Ethyl nitrite (EtONO) was used as a standard compound of nitrite ions for electrochemical measurements. Electrochemical determination of nitrite ions was performed by anodic linear sweep voltammetry in the first-order derivative mode (ALSV FOD) in Britton-Robinson (BR) buffer with pH 4.02 on carbon ink modified graphite electrode. EtONO calibrations were linear over a concentration range from 2 to 9 µmol L-1 with corresponding regression equation y = 0.768c - 0.048. Limit of detection (LOD) (S/N = 3) was 0.38 µmol L-1. The results of the study showed the fundamental possibility of using voltammetry to assess indirectly the production of nitric oxide by cells in supernatants of the monocytic macrophage lineage. The level of nitric oxide metabolites (nitrite ions) in supernatants was associated with the functional state of macrophages.

The Trace Detection of Nitrite Ions Using Neutral Red Functionalized SH-ß-Cyclodextrin @Au Nanoparticles.

A novel fluorescence sensor of NR-ß-CD@AuNPs was prepared for the trace detection of nitrite in quantities as low as 4.25 × 10-3 µg∙mL-1 in an aqueous medium. The fluorescence was due to the host-guest inclusion complexes between neutral red (NR) molecules and gold nanoparticles (AuNPs), which were modified by per-6-mercapto-beta-cyclodextrins (SH-ß-CDs) as both a reducing agent and a stabilizer under microwave radiation. The color of the NR-ß-CD@AuNPs changed in the presence of nitrite ions. A sensor was applied to the determination of trace nitrites in environmental water samples with satisfactory results.

Solid olive waste in environmental cleanup: enhanced nitrite ion removal by ZnCl2-activated carbon.

This communication describes how olive solid wastes can be used to prepare activated carbon (AC), with soundly high surface areas, suitable to remove nitrite ions from water. Solid olive wastes, so called Jeft, separated as unwanted bi-products from olive oil mills, have been converted into charcoal. The charcoal was then physically and/or chemically activated using different compounds namely conc. H3PO4 or ZnCl2. Charcoal carbonization was performed under inert atmosphere to avoid loss of heated carbon by oxidation with air. Surface area measurements and SEM micrographs showed that activation using ZnCl2 yields AC with highest surface area and more porous surfaces. The ZnCl2-activated carbon was then used to remove nitrite ions from water by adsorption. Effects of different parameters on value of surface area and adsorption capacity of the AC were investigated. Commercial AC materials were used as reference for comparison. The AC showed higher adsorption capacity toward nitrite than other reported adsorbents. The results suggest that using 5 g of the ZnCl2-activated carbon per liter of heavily nitrite-contaminated water (50 ppm) may bring the contaminant concentration down to the WHO accepted concentration limits within 60 min. This work highlights the future feasibility of using olive waste as feed stocks to produce useful renewable materials while keeping in mind the wisdom "make wastes work in environmental protection".

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.

Machine learning trained poly (3,4-ethylenedioxythiophene) functionalized carbon matrix suspended Cu nanoparticles for precise monitoring of nitrite from pickled vegetables.

Precise monitoring of nitrite from real samples has gained significant attention due to its detrimental impact on human health. Herein, we have fabricated poly(3,4-ethylenedioxythiophene) functionalized carbon matrix suspended Cu nanoparticles (PEDOT-C@Cu-NPs) through a facile green synthesis approach. Additionally, we have used machine learning (ML) to optimize experimental parameters such as pH, drying time, and concentrations to predict current of the designed electrochemical sensor. The ML optimized concentration of fabricated C@Cu-NPs was further functionalized by PEDOT (π-electron mediator). The designed PEDOT functionalized C@Cu-NPs (PEDOT-C@Cu-NPs) electrode has shown excellent electro-oxidation capability towards NO2- ions due to highly exposed Cu facets, defects rich graphitic C and high π-electron density. Additionally, the designed material has shown low detection limit (3.91 µM), high sensitivity (0.6372 µA/µM/cm2), and wide linear range (5-580 µM). Additionally, the designed electrode has shown higher electrochemical sensing efficacy against real time monitoring from pickled vegetables extract.

Variation of nitrate and nitrite in condensable particulate matter from coal-fired power plants under the simulated rapid condensing conditions.

In this work, condensation temperature, H2O vapor, SO2, SO3 and NH3 were studied to explore the formation mechanism of nitrate ions (NO3-) and nitrite ions (NO2-) in condensable particulate matter (CPM) discharged by ultra-low emission coal-fired power plants. Some important results were obtained: (i) The concentration of NO3- and NO2- increased with the decrease of condensation temperature, and H2O vapor could also promote the formation of NO3- and NO2-. (ii) The effects of SO2 and SO3 varied at different saturated states of flue gas, which was caused by the redox reaction of SO2 and NOX or the formation of H2SO4. (iii) NH3 could promote the nucleation of NO3- and NO2-, and the promotion effect also existed in the existence of SO2 or SO3. It is worth mentioning that SO3 and SO2 might synergistically inhibit the formation of NO3- and NO2-, regardless of the presence of NH3. The research results would enrich peoples understanding of the chemical and physical characteristics of NO3- and NO2- in CPM and provide a basic reference for the control of CPM emitted from coal-fired power plants.

Synthesis of fluorescent terbium-based metal-organic framework for quantitative detection of nitrite and ferric ions in water samples.

Through a solvothermal reaction between the corresponding lanthanide(III) nitrate, 1,10 o-phenanthroline and pyridine 3,5-dicarboxylic acid ligands, a novel two-dimensional terbium-based metal-organic framework (Tb-MOF), named {Tb2O0.5(C12H8N2)2(C7H3NO4)3(H2O)2.75}n (1) with strong fluorescence was synthesized by hydrothermal method. The single crystal structure and phase purity of the as-synthesized Tb-MOF were verified by single crystal X-ray diffraction. Subsequently, some studies on the morphology, structure, and optical properties of the compound were carried out. The results show that the synthesized Tb-MOF (1) can be used for the fluorescence sensing of nitrite and ferric ions. Simultaneously, the as-synthesized crystal structure offers good chemical stability in different environments, such as common organic solvents, solutions with a wide pH range, and aqueous solutions of metal ions. Besides, it has good chemical stability in a certain temperature range. In addition, a detection method for nitrite and iron ions was established based on the principle of fluorescence quenching of Tb-MOF by the analytical target, showing good recovery and precision. The proposed method provides a reliable new method for detecting nitrite and ferric ions concentrations in actual water samples.

New application for TiO2 P25 photocatalyst: A case study of photoelectrochemical sensing of nitrite ions.

Developing photoelectrochemical (PEC) sensors based on photocatalytic materials has recently attracted great interest as an emerging technology for environmental monitoring. TiO2 P25 is a well-known highly active photocatalyst, cheap, and produced commercially on a large scale. In the current work, a practical and durable TiO2-based PEC sensor has been fabricated by immobilizing TiO2 P25 nanoparticles at disposable screen-printed carbon substrates using drop-casting method. The fabricated PEC sensor has been applied for the anodic-detection and determination of nitrite (NO2-) ions under UV(A) light (LED, 365 nm) using chronoamperometry (CA) and differential pulse voltammetry (DPV). Linear calibration curves were obtained between the photocurrent responses and the concentrations of NO2- ions in the ranges of 0.1-5.0 and 0.5-10 mg L-1 for CA and DPV, respectively. Surprisingly, the detection limits (sensitivities) of the fabricated sensor towards NO2- ions under light were enhanced by a factor of 4.75 (4.1) and 8.3 (37.4) for CA and DPV, respectively, in comparsion with those measured in the dark. It is found that the photo-excitation of TiO2 facilitates the photooxidation of NO2- ions via the photo-generated holes whereas the photogenerated electrons contribute to the enhanced photocurrent and consequently the enhanced detection limit and sensitivity. The fabricated TiO2-based PEC sensor exhibits a good stability, durability, and satisfying selectivity for NO2- ions determination. These results indicate that the TiO2-based PEC sensor fabricated by utilizing cheap and commercially available components has great potential for being transferred from lab-to-factory.

4-Aminothiophenol capped halloysite nanotubes/silver nanoparticles as surface-enhanced Raman scattering probe for in-situ derivatization and selective determination of nitrite ions in meat product.

Halloysite nanotubes loaded with 4-aminothiophenol capped silver nanoparticles (mHNTs-AgNPs4-ATP) composite was synthesized as a sensitive surface-enhanced Raman scattering (SERS) probe for the determination of nitrite ions in sausage and pork luncheon meat. The as-prepared composite was characterized by transmission electron microscope, X-ray diffraction spectroscopy and Fourier transform infrared spectroscopy. The as-synthesized mHNTs-AgNPs4-ATP composite with evenly distribution of AgNPs can provide in-situ derivatization site for sensitive and selective SERS detection of nitrite ions. Under acid condition, the 4-ATP capped on the AgNPs can be transformed into p,p'-dimercaptoazobenzene (DMAB) through nitrite-triggered diazo reaction. This efficient nitrite-triggered reaction can be used to detect nitrite via the characteristic peaks of DMAB at 1143 cm-1, 1392 cm-1, and 1434 cm-1. This SERS method has a wide logarithmic range of 0.0069-6.9 mg L-1, with detection limit of 0.78, 3.4, 0.51 µg L-1 at the peak of 1143 cm-1, 1392 cm-1, and 1434 cm-1, respectively. Besides, this method can be applied to detect nitrite ions in sausage and pork luncheon meat with relative standard deviation less than 10.3%, and the results were consistent with that analyzed by UV-Vis method. This method has good potential in efficient detection of meat product in food safety.

Hyperpolarized [15N]nitrate as a potential long lived hyperpolarized contrast agent for MRI.

Reports on gadolinium deposits in the body and brains of adults and children who underwent contrast-enhanced MRI examinations warrant development of new, metal free, contrast agents for MRI. Nitrate is an abundant ion in mammalian biochemistry and sodium nitrate can be safely injected intravenously. We show that hyperpolarized [15N]nitrate can potentially be used as an MR tracer. The 15N site of hyperpolarized [15N]nitrate showed a T1 of more than 100 s in aqueous solutions, which was prolonged to more than 170 s below 20 °C. Capitalizing on this effect for polarization storage we obtained a visibility window of 9 min in blood. Conversion to [15N]nitrite, the bioactive reduced form of nitrate, was not observed in human blood and human saliva in this time frame. Thus, [15N]nitrate may serve as a long-lived hyperpolarized tracer for MR. Due to its ionic nature, the immediate applications appear to be perfusion and tissue retention imaging.

Highly fluorescent N-doped carbon nanodots as an effective multi-probe quenching system for the determination of nitrite, nitrate and ferric ions in food matrices.

Tris-(hydroxymethyl)-aminomethane and urea were used as low-cost precursor compounds to synthesize highly fluorescent N-doped carbon nanodots (CNDs), in an environmentally-friendly, inexpensive process. The as-prepared CNDs exhibit blue fluorescence, excellent photostability under various conditions, water dispersibility and stability over several parameters, such as a wide range of pH. The N-doped CNDs were applied as a multi-probe fluorescence quenching system to the sensitive detection of nitrite (NO2-), nitrate (NO3-) and ferric (Fe3+) ions in food matrices. The recoveries from spiked food samples were fairly acceptable without significant interferences despite the complexity of the tested matrices. The decrease in fluorescence intensity is in linear relationship with the concentrations of NO2-, NO3- and Fe3+, in the ranges of 0.015-1.11 mM, 0.072-0.60 mM and 2.9-176 µΜ, respectively. The as-synthesized carbon dots were used for the detection of NO2-, NO3- and Fe3+ in food matrices after proper pretreatment, concluding that the multi-probe fluorescence system may potentially be implemented in food control. The FRET mechanism is able to describe the quenching of the CNDs-NO2- system, while the proportional temperature-dependent relationship with the slopes of calibration plots hint at a dynamic quenching mechanism. In the case of the CNDs-Fe3+ system, the slopes exhibit an inverse temperature dependence, indicating a static mechanism while there is no indication of a FRET mechanism.

Gold dendrites Co-deposited with M13 virus as a biosensor platform for nitrite ions.

We developed a biosensor for nitrite ion on an electrode surface modified with M13 viruses and gold nanostructures. Gold dendritic nanostructures (Au-DNs) are electrochemically co-deposited from 4E peptides engineered M13 virus (M134E) mixed electrolyte on to the ITO electrode. The M134E could specifically nucleate Au precursor (Gold (III) chloride), which enable the efficient growth of dendritic nanostructures, whereas such dendritic structures were not obtained in the presence of wild-type and Y3E peptides engineered M13 viruses. The structural features of the Au-DNs and their interfacing mechanism with ITO electrode are characterized by SEM, EDX and XRD analyses. The growth of Au-DNs at ITO electrode has been monitored by time dependent SEM study. The M134E induces the formation and plays a crucial role in shaping the dendritic morphology for Au. Biosensor electrode was constructed using Au-DNs modified electrode for nitrite ions and found improved sensitivity relative to the sensor electrode prepared from wild-type M13, Y3E peptides engineered M13 and without M13. Sensor electrode exhibited good selectivity toward target analyte from the possible interferences. Furthermore, 4E native peptides were used as additive to deposit Au nanostructures and it is compared with the structure and reactivity of the Au nanostructures prepared in the presence of M134E. Our novel biosensor fabrication can be extended to other metal and metal oxide nanostructures and its application might be useful to develop novel biosensor electrode for variety of biomolecules.

Composite of Cu metal nanoparticles-multiwall carbon nanotubes-reduced graphene oxide as a novel and high performance platform of the electrochemical sensor for simultaneous determination of nitrite and nitrate.

In the present research, we aimed to fabricate a novel electrochemical sensor based on Cu metal nanoparticles on the multiwall carbon nanotubes-reduced graphene oxide nanosheets (Cu/MWCNT/RGO) for individual and simultaneous determination of nitrite and nitrate ions. The morphology of the prepared nanocomposite on the surface of glassy carbon electrode (GCE) was characterized using various methods including scanning electron microscopy (SEM), atomic force microscopy (AFM), and electrochemical impedance spectroscopy. Under optimal experimental conditions, the modified GCE showed excellent catalytic activity toward the electro-reduction of nitrite and nitrate ions (pH=3.0) with a significant increase in cathodic peak currents in comparison with the unmodified GCE. By square wave voltammetry (SWV) the fabricated sensor demonstrated wide dynamic concentration ranges from 0.1 to 75µM with detection limits (3Sb/m) of 30nM and 20nM method for nitrite and nitrate ions, respectively. Furthermore, the applicability of the proposed modified electrode was demonstrated by measuring the concentration of nitrite and nitrate ions in the tap and mineral waters, sausages, salami, and cheese samples.