Electrochemical sensor based on carbon nanotube decorated with manganese oxide nanoparticles for naphthalene determination.

In this work, an electrochemical sensor was developed for the determination of naphthalene (NaP) in well water samples, based on a glass carbon electrode (GCE) modified as a nanocomposite of manganese oxides (MnOx) and COOH-functionalized multi-walled carbon nanotubes (MWCNT). The synthesis of MnOx nanoparticles was performed by the sol-gel method. The nanocomposite was obtained by mixing MnOx and MWCNT with the aid of ultrasound, followed by stirring for 24 h. Surface modification facilitated the electron transfer process through the MnOx/MWCNT/GCE composite, which was used as an electrochemical sensor. The sensor and its material were characterized by cyclic voltammetry (CV), transmission electron microscopy (TEM), scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDS), X-ray diffraction (XRD) and Fourier transform infrared spectroscopy (FTIR). Important parameters influencing electrochemical sensor performance (pH, composite ratios) were investigated and optimized. The MnOx/MWCNT/GCE sensor showed a wide linear range of 2.0-16.0 µM, a detection limit of 0.5 µM and a quantification limit of 1.8 µM, in addition to satisfactory repeatability (RSD of 7.8%) and stability (900 s) in the determination of NaP. The determination of NaP in a sample of water from a gas station well using the proposed sensor showed results with recovery between 98.1 and 103.3%. The results obtained suggest that the MnOx/MWCNT/GCE electrode has great potential for application in the detection of NaP in well water.

Electrosynthesis of three-dimensional nanoporous nickel on screen-printed electrode used for the determination of narirutin in citrus wastewater.

In this study, an electrochemical sensor was designed for the detection of narirutin using three-dimensional nanostructured porous nickel on screen-printed electrode (3DnpNi/SPE). The modified electrode was successfully synthesized by the dynamic hydrogen bubble template method. The 3DnpNi/SPE was characterized by spectroscopic, microscopic, and electrochemical methods. The results showed that the 3DnpNi/SPE presents good electrocatalytic activity for the oxidation of narirutin. The quantification of narirutin was conducted by differential pulse voltammetry, which showed a wide concentration range (1.0 × 10-7 - 1.0 × 10-5 mol L-1), with low detection limit (3.9 × 10-8 mol L-1), and excellent sensitivity (0.31 A L mol-1). The proposed electrode was applied toward the determination of narirutin in yellow water sample from the citrus industry, where it presented a good degree of accuracy. The 3DnpNi/SPE showed repeatability, long-term stability, and selectivity. The results obtained showed agreement with those obtained by HPLC/DAD method. Chemical compounds studied in this article.

Non-enzymatic lactose molecularly imprinted sensor based on disposable graphite paper electrode.

Lactose (LAC) is a disaccharide - major sugar, present in milk and dairy products. LAC content is an important indicator of milk quality and abnormalities in food industries, as well as in human and animal health. The present study reports the development of an innovative imprinted voltammetric sensor for sensitive detection of LAC. The sensor was constructed using electropolymerized pyrrole (Py) molecularly imprinted polymer (MIP) on graphite paper electrode (PE). The MIP film was constructed through the electrosynthesis of polypyrrole (PPy) in the presence of LAC (template molecule) on PE (PPy/PE). To optimize the detection conditions, several factors affecting the PPy/PE sensor performance were assessed by multivariate methods (Plackett-Burman design and central composite design). Under optimized conditions, the proposed analytical method was applied for LAC detection in whole and LAC-free milks, where it demonstrated high sensitivity and selectivity, with two dynamic linear ranges of concentration (1.0-10 nmol L-1 and 25-125 nmol L-1) and a detection limit of 0.88 nmol L-1. The MIP sensor showed selective molecular recognition for LAC in the presence of structurally related molecules. The proposed PPy/PE sensor exhibited good stability, as well as excellent reproducibility and repeatability. Based on the results obtained, the PPy/PE is found to be highly promising for sensitive detection of LAC.

Amperometric determination of myo-inositol by using a glassy carbon electrode modified with molecularly imprinted polypyrrole, reduced graphene oxide and nickel nanoparticles.

This paper reports on the development of an amperometric method for the determination of myo-inositol. The method involves coating of a glassy carbon electrode (GCE) with a molecularly imprinted polymer (MIP) and reduced graphene oxide (RGO) that was modified with nickel nanoparticles (NiNPs). The MIP was prepared by electropolymerization of pyrrole on the surface of the GCE in the presence of myo-inositol molecules. The construction steps of the modified electrode were monitored via cyclic voltammetry, atomic force microscopy, scanning electron microscopy and X-ray Photoelectron Spectroscopy. The results were evaluated using differential pulse voltammetry, in which hexacyanoferrate was used as an electrochemically active probe. Under optimized experimental conditions, the imprint-modified GCE has a linear response in the 1.0 × 10-10 mol L-1 to 1.0 × 10-8 mol L-1 concentration range, with a 7.6 × 10-11 mol L-1 detection limit and an electrochemical sensitivity of 4.5 µA·cm-2 µmol-1. The method showed improved selectivity even in the presence of molecules with similar chemical structure. The GCE modified was successfully applied to the determination of myo-inositol in sugarcane vinasse where it yielded recoveries that ranged from 95 to 102%. Graphical abstract Schematic presentation of molecularly imprinted polymer (MIP) on a glassy carbon electrode (GCE) modified with nickel nanoparticles (NiNP) anchored in reduced graphene oxide (RGO). The resulting MIP/NiNP/RGO-GCE was used for indirect determination of myo-inositol.

D-mannitol sensor based on molecularly imprinted polymer on electrode modified with reduced graphene oxide decorated with gold nanoparticles.

An electrochemical sensor for D-mannitol based on molecularly imprinted polymer on electrode modified with reduced graphene oxide decorated with gold nanoparticles was developed in this present work. The sensor was constructed for the first time via the electropolymerization of o-phenylenediamine (o-PD) over a surface containing reduced graphene oxide (RGO) and gold nanoparticles (AuNP) in the presence of D-mannitol molecules. The surface modification with AuNP/RGO-GCE facilitated the charge transfer processes of [Fe(CN)6]3-/4-, which was used as an electrochemical probe. It also contributed meaningfully towards the increase in the surface/volume ratio, creating more locations for imprinting, and providing greater sensitivity to the sensor. The MIP/AuNP/RGO-GCE sensor was characterized by cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS), scanning electron microscope (SEM), atomic force microscope (AFM) and X-ray Photoelectron Spectroscopy (XPS). Important parameters that exert control over the performance of the molecularly imprinted sensor (such as number of cycles, pH, monomer and template concentration and extraction and rebinding conditions) were investigated and optimized. The imprinting factor was 4.9, showing greater response to the D-mannitol molecule compared to the interfering molecules. The limit of detection, limit of quantification and amperometric sensitivity were 7.7×10-13molL-1, 2.6×10-12molL-1 and 3.9×1010µALmol-1 (n=3) respectively. The MIP/AuNP/RGO-GCE sensor was successfully applied towards the selective determination of D-mannitol in sugarcane vinasse, thus making it, in essence, a valuable tool for the accurate and reliable determination of this molecule.

Determination of furanic aldehydes in sugarcane bagasse by high-performance liquid chromatography with pulsed amperometric detection using a modified electrode with nickel nanoparticles.

A glassy carbon electrode chemically modified with nickel nanoparticles coupled with reversed-phase chromatography with pulsed amperometric detection was used for the quantitative analysis of furanic aldehydes in a real sample of sugarcane bagasse hydrolysate. Chromatographic separation was carried out in isocratic conditions (acetonitrile/water, 1:9) with a flow rate of 1.0 mL/min, a detection potential of -50 mV vs. Pd, and the process was completed within 4 min. The analytical curves presented limits of detection of 4.0 × 10-7 mol/L and 4.3 × 10-7 mol/L, limits of quantification of 1.3 × 10-6 and 1.4 × 10-6 mol/L, amperometric sensitivities of 2.2 × 106 nA mol/L and 2.7 × 106 nA mol/L for furfural and 5-hydroxymethylfurfural, respectively. The values obtained in this sample by the standard addition method were 1.54 ± 0.02 g/kg for 5-hydroxymethylfurfural and 11.5 ± 0.2 g/kg for furfural. The results demonstrate that this new proposed method can be used for the quick detection of furanic aldehydes without the interference of other electroactive species, besides having other remarkable merits that include excellent peak resolution, analytical repeatability, sensitivity, and accuracy.