Electrochemical detection of nitrite and ascorbic acid at glassy carbon electrodes modified with carbon nano-onions bearing electroactive moieties

Electrochemical determination of ascorbic acid using sensitive and disposable methylene blue modified pencil graphite electrode

In the present work, a convenient, efficient and disposable electrochemical sensor has been developed by electropolymerizing methylene blue (PMB) on the surface of a pencil graphite electrode (PGE), which facilitates the electrochemical analysis of an antioxidant l-Ascorbic Acid (AA). The structural characteristics of both the methylene blue modified pencil graphite electrode (PMB/PGE) and the bare pencil graphite electrode (BPGE) have been examined using scanning electron microscopy (SEM) in conjunction with energy-dispersive X-ray analysis (EDX). Additionally, the charge transfer behavior has been evaluated using the electron impedance spectroscopy (EIS). The voltammetric response of AA has been examined using different methods, such as differential pulse voltammetry (DPV) and linear sweep voltammetry (LSV). This exploration has been carried out in 0.1 M phosphate buffer solution (PBS) of physiological pH 7.0. The electrochemical sensor PMB/PGE proposed in this study exhibited an improved peak current and a slight negative shift in peak potential for AA compared to bare electrode. The enhancement in peak current at the modified electrode has been attributed to the electrocatalytic characteristics of the modifiers. The limit of detection (LOD) for AA has been determined using the differential pulse voltammetry (DPV), with concentrations ranging from 1.0 μM to 12.0 μM. The calculated LOD value has been found to be 0.15 μM. The selectivity and practicality of the modified electrode has been assessed through the real sample analysis and demonstrating its capability to detect AA in the presence of paracetamol (PA) resulting in satisfactory recovery results. Hence the proposed sensor could be successfully validated for the determination of AA in pharmaceutical sample.

Application of Chitosan@Fe3O4 Nanoparticle-Modified Screen-Printed Graphene-Based Electrode for Simultaneous Analysis of Nitrite and Ascorbic Acid in Hydroponics and Fruit Juice

In this work, the development of screen-printed electrodes modified with chitosan-coated magnetite nanoparticles (CTS@Fe3O4/SPGNE) for the simultaneous determination of nitrite (NO2-) and ascorbic acid (AA-) is presented. The study investigated various ratios of graphene to chitosan-coated magnetite nanoparticles (CTS@Fe3O4), as well as the optimal pH. These factors were examined due to their impact on the selectivity and sensitivity of the analysis. The results indicated that a graphene paste to CTS@Fe3O4 ratio of 16:1.0 g and a pH of 4 were optimal for the analysis of both NO2- and AA-. Additionally, the behavior of the proposed electrode, its analytical performance, and interference studies were thoroughly examined. Furthermore, the CTS@Fe3O4/SPGNE electrode shows potential for the simultaneous determination of NO2- and AA- in hydroponics and fruit juice samples.

Carbon Nano-Onion Peroxidase Composite Biosensor for Electrochemical Detection of 2,4-D and 2,4,5-T

Carbon nano-onions are emerging electrode materials in biosensing due to their high conductivity and biocompatibility. Phenoxy-based herbicides are a source of environmental contamination that can be detected using their property to inhibit the activity of some enzymes. Here we report a biosensor based on peroxidase immobilized on carbon nano-onions in a cyclodextrin polymer matrix for the amperometric detection of 2,4-D and 2,4,5-T. The inhibition mechanism of 2,4-D and 2,4,5-T on peroxidase activity was first elucidated by activity measurements and molecular docking. The biosensor was characterized by electrochemical and microscopy methods and applied to the amperometric detection of these herbicides. The incorporation of carbon nano-onions enhanced the sensitivity of the biosensor and improved its stability and repeatability. The application of the developed biosensor to the detection of 2,4-D in soil and 2,4,5-T in river water samples is also reported.

Tailoring the performance of electrochemical biosensors based on carbon nanomaterials via aryldiazonium electrografting

Carbon nanomaterials (CNs) offer some of the most valuable properties for electrochemical biosensing applications, such as good electrical conductivity, wide electrochemical stability, high specific surface area, and biocompatibility. Regardless the envisioned sensing application, endowing CNs with specific functions through controlled chemical functionalization is fundamental for promoting the specific binding of the analyte. As a versatile and straightforward method of surface functionalization, aryldiazonium chemistry have been successfully used to accommodate in a stable and reproducible way different functionalities, while the electrochemical route has become the favourite choice since the deposition conditions can be readily controlled and adapted to the substrate. In particular, the modification of CNs by electrochemical reduction of aryl diazonium salts is established as a powerful tool which allows tailoring the chemical and electronic properties of the sensing platform. By outlining the stimulating results disclosed in the last years, this article provides not only a comprehensively review, but also a rational assessment on contribution of aryldiazonium electrografting in developing CNs-based electrochemical biosensors. Furthermore, some of the emerging challenges to be surpassed to effectively implement this methodology for in vivo and point of care analysis are also highlighted.

Carbon Nano-onions: A Valuable Class of Carbon Nanomaterials in Biomedicine

The development of nanoscale materials is an important area of research as it provides access to materials with unique properties that can be applied to improve quality of life. Multi-layer fullerenes, also known as carbon nano-onions (CNOs) are an exciting class of nanostructures which show great versatility and applicability. They find applications in several fields of technology and biomedicine. This review highlights the potential advantages of CNOs for biomedical applications, which include but are not limited to bioimaging and sensing. Their good biocompatibility renders them promising platforms for the development of novel healthcare devices.

Application of Graphene-Based Materials for Detection of Nitrate and Nitrite in Water-A Review

Nitrite and nitrate are widely found in various water environments but the potential toxicity of nitrite and nitrate poses a great threat to human health. Recently, many methods have been developed to detect nitrate and nitrite in water. One of them is to use graphene-based materials. Graphene is a two-dimensional carbon nano-material with sp² hybrid orbital, which has a large surface area and excellent conductivity and electron transfer ability. It is widely used for modifying electrodes for electrochemical sensors. Graphene based electrochemical sensors have the advantages of being low cost, effective and efficient for nitrite and nitrate detection. This paper reviews the application of graphene-based nanomaterials for electrochemical detection of nitrate and nitrite in water. The properties and advantages of the electrodes were modified by graphene, graphene oxide and reduced graphene oxide nanocomposite in the development of nitrite sensors are discussed in detail. Based on the review, the paper summarizes the working conditions and performance of different sensors, including working potential, pH, detection range, detection limit, sensitivity, reproducibility, repeatability and long-term stability. Furthermore, the challenges and suggestions for future research on the application of graphene-based nanocomposite electrochemical sensors for nitrite detection are also highlighted.

Amperometric biosensor for glyphosate based on the inhibition of tyrosinase conjugated to carbon nano-onions in a chitosan matrix on a screen-printed electrode

Glyphosate [N-(phosphonomethyl)glycine] is the most frequently used herbicide to date. Due to its indiscriminate use, it has become a globally occurring pollutant of surface waters. A biosensor for glyphosate is described here that consists of a carbon nano-onion/tyrosinase conjugate immobilized in a chitosan matrix on a screen-printed electrode. The analytical principle is based on the inhibition of the enzyme tyrosinase by glyphosate. L-DOPA is used as the enzyme substrate. The presence of the carbon nano-onions has a beneficial effect on the sensitivity of the assay. Glyphosate can be amperometrically quantified in the 0.015 to 10 μM concentration range and with a 6.5 nM (1.1 μg L-1) detection limit. The biosensor is stable more than 2 months at 4 °C. It was applied to the detection of glyphosate in water and soil samples taken from irrigation of a rice field after aerial application. Results were in good agreement with data obtained by a commercial ELISA. Graphical abstract A highly sensitive amperometric biosensor for glyphosate is reported, based on the covalent immobilization of a carbon nano-onion/tyrosinase conjugate on a chitosan matrix.

A reversible and dual responsive sensing approach for determination of ascorbate ion in fruit juice, biological, and pharmaceutical samples by use of available triaryl methane dye and its application to constructing a molecular logic gate and a set/reset memorized device

Since dyes are available in huge quantities and have the well-established chemistry involved in their synthesis, their use in chemosensing could be continued. In the current study, a new and reversible colorimetric and fluorometric chemosensor based on available triaryl methane dye (brilliant green (BG)) - phosphotungstic acid (PTA) complex has been designed for determination of ascorbate (AscH^-1) ion in water/DMSO (90:10v/v, 1.0mmolL^-1 HEPES, pH7.0). The "ON-OFF" fluorescence and colorimetric responses of this ion association complex to AscH^-1 were based on a displacement mechanism. For the detection of AscH^-1, the linear ranges achieved for UV-Vis absorbance and fluorescence experiments were 3.9-62.6μmolL^-1 and 1.9-85.4μmolL^-1, respectively. The limits of detection for both of them were also calculated to be 0.4 and 0.2μmolL^-1. The proposed method was also successfully utilized for rapid recognition of ascorbate in juice samples, human serum, and the formulation of supplement products. Moreover, the proposed chemosensor capability of functioning as INHIBITION-type sensor with PTA and AscH^-1 as chemical inputs was indicated by the investigation of the molecular logic behavior of this chemosensor. Eventually, a sequential memory unit displaying "Write-Read-Erase-Read" function could be integrated based on the reversible and reproducible system.

Highly sensitive detection of nitrite by using gold nanoparticle-decorated α-Fe2O3 nanorod arrays as self-supporting photo-electrodes

Gold nanoparticle (Au NP)-decorated-Fe₂O₃ nanorod arrays (AuNPs-Fe₂O₃) as a photoelectrode are applied to the detection of nitrite solution with a low limit of detection and high sensitivity.

Onion-Like Carbon Nanostructures: An Overview of Bio-Applications

This article presents a brief review of the knowledge concerning onion-like carbons (OLCs). These nanostructures are some of the most fascinating carbon forms due to their unusual structure and physico-chemical properties. Generally, OLCs consist of a hollowspherical fullerene core surrounded by concentric graphitic layers with increasing diameter. Nevertheless, they can have different size, shape and type of core, which determine their physicochemical properties. In this article, we review the most important literature reports in this area and briefly describe these nanostructures, their physical and chemical properties and their potential uses with a focus on biomedicine.