In situ formed zinc oxide/graphitic carbon nitride nanohybrid for the electrochemical determination of 4-nitrophenol.

The electrochemical determination of 4-nitrophenol using a nanohybrid consisting of glassy carbon (GC) and zinc oxide/graphitic carbon nitride (ZnO/g-CN nanosheet), is described. The ZnO/g-CN nanohybrid was in situ synthesized by chemical method and well characterized using absorption spectroscopy, X-ray diffraction, X-ray photoelectron spectroscopy and transmission electron microscopic analysis. It was observed that the nanosized ZnO particles were present inside the sheet-like g-CN nanostructure. The nanohybrid-modified electrode showed an enhanced electrocatalytic response for 4-nitrophenol reduction compared with the bare GC electrode. The assay exhibited linear ranges of 13.4-100 µM and 100-1000 µM for 4-NP determination. The limit of detection and limit of quantification were 4.0 and 13.4 µM, respectively, at the working potential of - 0.85 V. An appreciable precision was found towards the stability of the assay in the determination. It provides selectivity against inorganic and organic substances such as calcium chloride, potassium chloride, nitrobenzene, uric acid, 1-chloro,2,4-dinitrobenzene, 1-bromo,2-nitrobenzene and 1-iodo,2-nitrobenzene. The practical applicability of the assay was also checked in the analysis of real water samples and satisfactory recovery of 4-NP was found. Schematic representation of the synthesis of zinc oxide (ZnO) nanostructures incorporated graphitic carbon nitride nanosheets (g-C3N4 NSs) and its application in the voltammetric determination of 4-nitrophenol (4-NP) is presented. The nanohybrid assay showed selectivity among coexisting compounds and good recovery in real sample analysis.

Iron oxide nanoparticle core-shell magnetic microspheres: Applications toward targeted drug delivery.

This study describes a sensitive reactive oxygen species (ROS)-responsive lecithin (LEC) incorporated iron oxide nanoparticle (Fe3O4 NP) system with potent anti-inflammatory properties and even more so when the antioxidant drug curcumin (CUR) is encapsulated in the PLGA hybrid magnetic microsphere system (Fe3O4@LEC-CUR-PLGA-MMS). The delivery system is responsive to ROS including an H2O2 environment to release the payload (CUR) drug. Greater cytotoxicity properties were observed in the presence of Fe3O4@LEC-CUR-PLGA-MMS against A549 and HeLa S3 cells with IC50 values after 24 h of 10 and 12 µg/mL and 10 and 20 µg/mL, respectively. The present Fe3O4@LEC-CUR-PLGA-MMS system demonstrated much better in vitro cytotoxicity, cellular morphological changes and moreover an ability to limit colony formation for A549 and HeLa S3 cancer cell lines than non-cancerous cells, and thus, should be further studied for a wide range of medical applications.

Electrocatalytic Reduction of Hydrogen Peroxide and Its Non-Enzymatic Electrochemical Detection Using Silver Nanoparticles Anchored on Reduced Graphene Oxide.

Silver-reduced graphene oxide (Ag-rGO) nanohybrid was synthesized by applying a slight modification to the Turkevich method using trisodium citrate as a reducing and stabilizing agent to catalyze the non-enzymatic electrochemical detection of hydrogen peroxide (H2O2). Spherical silver nanoparticles (AgNPs) with an average particle size of 2.2 nm surfaced on reduced graphene oxide (rGO) sheets. Cyclic voltammograms (CV) obtained from glassy carbon (GC) electrode coated with Ag-rGO nanohybrid (4 mM) exhibited a peak at an overpotential of -0.52 V, with a larger faradaic current for the reduction of H2O2. Using the modified electrode for the linear sweep voltammetry (LSV) detection of H2O2, the detection limit and sensitivity were determined to be 4.8 µM (S/N ═ 3) and 0.0262 µA µM-1, respectively. The sensor appeared selective and stable towards H2O2 in the presence of possible interference, and it also demonstrated good recoveries of H2O2 concentration in real water samples.

A cobalt oxide nanocubes interleaved reduced graphene oxide nanocomposite modified glassy carbon electrode for amperometric detection of serotonin.

Cobalt oxide nanocubes incorporated with reduced graphene oxide (rGO-Co3O4) was prepared by using simple one-step hydrothermal route. Crystallinity and structural characteristics of the nanocomposite were analyzed and confirmed using X-ray diffraction (XRD) and Raman analysis, respectively. The cubical shape of the Co3O4 nanostructures and the distribution of Co3O4 nanocubes on the surface of rGO sheets were identified through field emission scanning electron microscopy (FESEM) and energy dispersive X-ray (EDX) mapping analysis, respectively. Raman spectra depicted the presence of D and G bands for GO and rGO with different ID/IG values and thus confirmed the reduction of GO into rGO. The electrochemical study reflects that the rGO-Co3O4 nanocomposite shows good electrocatalytic activity in oxidation of depression biomarker serotonin (5-HT) in phosphate buffer (pH 7.2). The detection of 5-HT was carried out by using rGO-Co3O4 nanocomposite modified glassy carbon electrode under dynamic condition using amperometry technique with a linear range of 1-10 µM. The limit of detection and limit of quantification were calculated and found to be 1.128 and 3.760 µM, respectively with a sensitivity value of 0.133 µΑ·µM-1. The sensor showed selectivity in the presence of different interferent species such as ascorbic acid, dopamine and uric acid.

Amperometric determination of L-cysteine using a glassy carbon electrode modified with palladium nanoparticles grown on reduced graphene oxide in a Nafion matrix.

An amperometric sensor for L-Cys is described which consists of a glassy carbon electrode (GCE) that was modified with reduced graphene oxide placed in a Nafion film and decorated with palladium nanoparticles (PdNPs). The film was synthesized by a hydrothermal method. The PdNPs have an average diameter of about 10 nm and a spherical shape. The modified GCE gives a linear electro-oxidative response to L-Cys (typically at +0.6 V vs. SCE) within the 0.5 to 10 µM concentration range. Other figures of merit include a response time of less than 2 s, a 0.15 µM lower detection limit (at signal to noise ratio of 3), and an analytical sensitivity of 1.30 µA·µM-1·cm-2. The sensor displays selectivity over ascorbic acid, uric acid, dopamine, hydrogen peroxide, urea, and glucose. The modified GCE was applied to the determination of L-Cys in human urine samples and gave excellent recoveries. Graphical abstract Spherical palladium nanoparticles (PdNPs) on reduced graphene oxide-Nafion (rGO-Nf) films were synthesized using a hydrothermal method. This nanohybrid was used for modifying a glassy carbon electrode to develop a sensor electrode for detecting L-cysteine that has fast response (less than 2 s), low detection limit (0.15 µM), and good sensitivity (0.092 µA µM-1 cm-2).

Ternary nanohybrid of reduced graphene oxide-nafion@silver nanoparticles for boosting the sensor performance in non-enzymatic amperometric detection of hydrogen peroxide.

A sensitive and novel electrochemical sensor was developed for the detection of hydrogen peroxide (H2O2) using a reduced graphene oxide-nafion@silver6 (rGO-Nf@Ag6) nanohybrid modified glassy carbon electrode (GC/rGO-Nf@Ag6). The GC/rGO-Nf@Ag6 electrode exhibited an excellent electrochemical sensing ability for determining H2O2 with high sensitivity and selectivity. The detection limit of the electrochemical sensor using the GC/rGO-Nf@Ag6 electrode for H2O2 determination was calculated to be 5.35×10-7M with sensitivity of 0.4508µAµM-1. The coupling between rGO-Nf with silver nanoparticles (AgNPs) significantly boosted the electroanalytical performance by providing more active area for analyte interaction, thereby allowing more rapid interfacial electron transfer process. The interfering effect on the current response of H2O2 was studied and the results revealed that the sensor electrode exhibited an excellent immunity from most common interferents. The proposed non-enzymatic electrochemical sensor was used for determining H2O2 in apple juice, and the sensor electrode provided satisfactory results with reliable recovery values. These studies revealed that the novel GC/rGO-Nf@Ag6 sensor electrode could be a potential candidate for the detection of H2O2.

Facile synthesis of graphene oxide-silver nanocomposite and its modified electrode for enhanced electrochemical detection of nitrite ions.

In this report, silver nanoparticles (Ag NPs) were successfully deposited on graphene oxide (GO) sheets to form GO-Ag nanocomposite using garlic extract and sunlight and the nanocomposite modified glassy carbon (GC) electrode was applied as an electrochemical sensor for the detection of nitrite ions. The formation of GO-Ag nanocomposite was confirmed by using UV-visible absorption spectroscopy, TEM, XRD and FTIR spectroscopy analyses. Further, TEM pictures showed a uniform distribution Ag on GO sheets with an average size of 19 nm. The nanocomposite modified electrode produced synergistic catalytic current in nitrite oxidation with a negative shift in overpotential. The limit of detection (LOD) values were found as 2.1 µM and 37 nM, respectively using linear sweep voltammetry (LSV) and amperometric i-t curve techniques. The proposed sensor was stable, reproducible, sensitive and selective toward the detection nitrite and could be applied for the detection of nitrite in real water sample.