Cooperative effect of Pt nanoparticles and Fe(III) in the electrocatalytic oxidation of nitrite

Development of electrochemical sensors for quick detection of environmental (soil and water) NPK ions

All over the world, technology is becoming more and more prevalent in agriculture. Different types of instruments are already being used in this sector. For the time being, every farmer is trying to produce more crops on a piece of land. Eventually, soil loses its nutrients; however, to grow more crops, farmers use more fertilizers without knowing the proper conditions of the soil in real time. To overcome this issue, many scientists have recently focused on developing electrochemical sensors to detect macronutrients, i.e., nitrogen (N), phosphorus (P), and potassium (K), in soil or water rapidly. In this review, we focus mainly on the recent developments in electrochemical sensors used for the detection of nutrients (NPK) in different types of samples. As it is outlined, the use of smart and portable electrochemical sensors can be helpful for the reduction of excess fertilizer and can play a vital role in maintaining suitable conditions in soils and water. We are optimistic that this review can guide researchers in the development of a portable and suitable NPK detection system for soil nutrients.

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.

Solid-State Heating Synthesis of Poly (3,4-Ethylenedioxythiophene)/Gold/Graphene Composite and Its Application for Amperometric Determination of Nitrite and Iodate

A ternary composite of poly (3,4-ethylenedioxythiophene)/gold/graphene (PEDOT/Au/GO) for promising electrochemical sensor was synthesized by solid-state heating method. The interaction between the PEDOT, Au, and GO explored for detection of nitrite and iodate. It was found that the PEDOT/Au/GO composite had shale-like morphology with a uniform distribution of gold nanoparticles. Electrochemical experiments showed that the PEDOT/Au/GO composite modified electrode exhibited good electrocatalytic activity toward determination of iodate. The amperometric experiments at the PEDOT/Au/GO/GCE revealed that a good linear relationship existed between peak current and the concentration in the range of 100-1000 μM with the detection of 0.53 and 0.62 μM (S/N = 3) for nitrite and iodate, respectively. Moreover, the current response of PEDOT/Au/GO/GCE for nitrite and iodate at 10 μM was up to 9.59 and 11.47 μA, respectively. Mechanisms of the direct electron transfer between ion(nitrite or iodate)and the PEDOT/Au/GO composite.

Methods for the detection and determination of nitrite and nitrate: A review

Various techniques for the determination of nitrite and/or nitrate developed during the past 15 years were reviewed in this article. 169 references were covered. The detection principles and analytical parameters such as matrix, detection limits and detection range of each method were tabulated. The advantages and disadvantages of various methods were evaluated. In comparison to other methods, spectrofluorimetric methods have become more attractive due to its facility availability, high sensitivity and selectivity, low limits of detection and low-cost.

Toward point-of-care management of chronic respiratory conditions: Electrochemical sensing of nitrite content in exhaled breath condensate using reduced graphene oxide

We present a portable non-invasive approach for measuring indicators of inflammation and oxidative stress in the respiratory tract by quantifying a biomarker in exhaled breath condensate (EBC). We discuss the fabrication and characterization of a miniaturized electrochemical sensor for detecting nitrite content in EBC using reduced graphene oxide. The nitrite content in EBC has been demonstrated to be a promising biomarker of inflammation in the respiratory tract, particularly in asthma. We utilized the unique properties of reduced graphene oxide (rGO); specifically, the material is resilient to corrosion while exhibiting rapid electron transfer with electrolytes, thus allowing for highly sensitive electrochemical detection with minimal fouling. Our rGO sensor was housed in an electrochemical cell fabricated from polydimethyl siloxane (PDMS), which was necessary to analyze small EBC sample volumes. The sensor is capable of detecting nitrite at a low over-potential of 0.7 V with respect to an Ag/AgCl reference electrode. We characterized the performance of the sensors using standard nitrite/buffer solutions, nitrite spiked into EBC, and clinical EBC samples. The sensor demonstrated a sensitivity of 0.21 μA μM^-1 cm^-2 in the range of 20-100 μM and of 0.1 μA μM^-1 cm^-2 in the range of 100-1000 μM nitrite concentration and exhibited a low detection limit of 830 nM in the EBC matrix. To benchmark our platform, we tested our sensors using seven pre-characterized clinical EBC samples with concentrations ranging between 0.14 and 6.5 μM. This enzyme-free and label-free method of detecting biomarkers in EBC can pave the way for the development of portable breath analyzers for diagnosing and managing changes in respiratory inflammation and disease.

Preparation of Free-Standing and Flexible Graphene/Ag Nanoparticles/Poly(pyronin Y) Hybrid Paper Electrode for Amperometric Determination of Nitrite

A flexible and free-standing graphene-based hybrid paper was successfully fabricated by successive applications of vacuum filtration and electropolymerization. First, a suspension including graphene oxide (GO) and silver nanoparticles (AgNPs) was prepared, and GO/AgNPs paper was obtained by vacuum-filtration of this suspension through a membrane. This GO/AgNPs paper was transformed to rGO/AgNPs paper by using both chemical reduction with HI and thermal annealing procedures. rGO/AgNPs/poly(PyY) hybrid paper electrode was formed by electropolymerization of Pyronin Y (PyY) on rGO/AgNPs paper electrode from a PyY monomer-containing (pH 1.0) solution. Structural, chemical, and morphological characterization of this hybrid paper was carried out by scanning electron microscopy, X-ray photoelectron spectroscopy, X-ray diffraction, Raman spectroscopy, infrared spectroscopy, UV-vis absorption spectroscopy, four-point probe conductivity measurement, and cyclic voltammetry techniques. Electrooxidation of nitrite on rGO/AgNPs/poly(PyY) hybrid paper electrode has been achieved at 860 mV with a linear range of 0.1-1000 μM, sensitivity of 13.5 μAμM(-1)cm(-2), and a detection limit of 0.012 μM. Amperometry studies have shown that the hybrid paper electrode is suitable for amperometric determination of nitrite in both standard laboratory samples and real samples. Moreover, this paper electrode selectively detects nitrite even in the presence of 100-fold common ions and exhibits an excellent operational stability and good flexibility.

Large mesoporous carbons decorated with silver and gold nanoparticles by a self-assembly method: enhanced electrocatalytic activity for H2O2 electroreduction and sodium nitrite electrooxidation

The silver, gold nanoparticles were grown onto poly (diallyldimethyl ammoniumchloride, PDDA)-functionalized large mesoporous carbon (LMC) by simple self-assembly method. AuNPs or AgNPs/PDDA–LMC show superior electrocatalytic activity.

Innovative solid-state microelectrode for nitrite determination in a nitrifying granule

Nitrite is an intermediate of both nitrification and denitrification in biological removal of nitrogen from wastewater, and in situ measurement of nitrite concentration in a biofilm or microbial granules is highly desirable. However, a solid-state microelectrode for nitrite determination is not available yet In this work, a solid-state microelectrode was manufactured through electrochemical codeposition of Pt--Fe nanoparticles on a gold microelectrode fabricated using photolithography for in situ nitrite determination. This gold-based microelectrode could be used as a more cost-effective, efficient, and reliable alternative to the liquid membrane microelectrode. Nanoparticles with an average diameter of 50 nm were observed on the surface of the chemically modified electrode. A sigmoid peak at ca. 0.7 V (vs Ag/AgCl) was found on the linear sweep voltammogram in nitrite solutions by using the fabricated microelectrode. The peak height of the first-order derivative of the sigmoid peak was proportional to the nitrite concentration of 0.001--0.05 M and could be used for quantitative determination of nitrite. The detection limits (S/N = 3) were approximately 3 x 10(-5) M. The nitrite microprofiles of aerobic granules from a nitrifying reactor were measured with the microelectrode to demonstrate its potential applications with high spatial resolution.