Sonication-assisted preparation of a nanocomposite consisting of reduced graphene oxide and CdSe quantum dots, and its application to simultaneous voltammetric determination of ascorbic acid, dopamine and uric acid

A Facile Method to Synthesize CdSe-Reduced Graphene Oxide Composite with Good Dispersion and High Nonlinear Optical Properties

CdSe-reduced graphene oxide (CdSe/RGO) composites were synthesized by a hydrothermal method. CdSe/RGO composites with different mass ratios were prepared. The structure and morphology of CdSe/RGO composites were analyzed by X-ray diffraction (XRD), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The synthesis of CdSe/RGO complexes was successfully demonstrated by Fourier infrared (FT-IR) and Raman spectra. CdSe nanoparticles in the CdSe/RGO composite were uniformly dispersed on the graphene surface. The study found that oxygen-containing functional groups such as hydroxyl (-OH) and carboxyl (-COOH) groups in graphene played a decisive role in the dispersion of CdSe. The third-order nonlinear optical properties of CdSe/RGO composites were measured by a single beam Z-scan technique. The experimental results showed that composites exhibited two-photon absorption and self-focusing nonlinear refraction properties. Additionally, the third-order nonlinear susceptibility of the composite material was obviously enhanced, which was mainly due to the good dispersion of CdSe nanoparticles on graphene.

Copper Nanowires Modified with Graphene Oxide Nanosheets for Simultaneous Voltammetric Determination of Ascorbic Acid, Dopamine and Acetaminophen

Copper nanowires (Cu NWs) were modified with graphene oxide (GO) nanosheets to obtain a sensor for simultaneous voltammetric determination of ascorbic acid (AA), dopamine (DA) and acetaminophen (AC). The nanocomposite was obtained via sonication, and its structures were characterized by scanning electron microscopy (SEM), X-ray diffraction (XRD) and energy-dispersive X-ray spectroscopy (EDS). The electrochemical oxidation activity of the materials (placed on a glassy carbon electrode) was studied by cyclic voltammetry and differential pulse voltammetry. Due to the synergistic effect of Cu NWs and GO, the specific surface, electrochemical oxidation performance and conductivity are improved when compared to each individual component. The peaks for AA (-0.08 V), DA (+0.16 V), and AC (+0.38 V) are well separated. The sensor has wide linear ranges which are from 1-60 μM, 1-100 μM, and 1-100 μM for AA, DA, and AC, respectively, when operated in the differential pulse voltammetric mode. The detection limits are 50, 410 and 40 nM, respectively. Potential interferences by uric acid (20 μM), glucose (10 mM), NaCl (1 mM), and KCl (1 mM) were tested for AA (1 μΜ), DA (1 μΜ), and AC (1 μΜ) and were found to be insignificant. The method was successfully applied to the quantification of AA, DA, and AC in spiked serum samples.

Golf ball-like MoS2 nanosheet arrays anchored onto carbon nanofibers for electrochemical detection of dopamine

Arrays of molybdenum(IV) disulfide nanosheets resembling the shape of golf balls (MoS₂ NSBs) were deposited on carbon nanofibers (CNFs), which are shown to enable superior electrochemical detection of dopamine without any interference by uric acid. The MoS₂ NSBs have a diameter of ∼ 2 μm and are made up of numerous bent nanosheets. MoS₂ NSBs are connected by the CNFs through the center of the balls. Figures of merit for the resulting electrode include (a) a sensitivity of 6.24 μA·μM^-1·cm^-2, (b) a low working voltage (+0.17 V vs. Ag/AgCl), and (c) a low limit of detection (36 nM at S/N = 3). The electrode is selective over uric acid, reproducible and stable. It was applied to the determination of dopamine in spiked urine samples. The recoveries at levels of 10, 20 and 40 μM of DA are 101.6, 99.8 and 107.8%. Graphical abstract Schematic presentation of the golf ball-like MoS₂ nanosheet balls/carbon nanofibers (MoS₂ NSB/CNFs) by electrospining and hydrothermal process to detect dopamine (DA).

Electrochemical sensor based on a nanocomposite prepared from TmPO4 and graphene oxide for simultaneous voltammetric detection of ascorbic acid, dopamine and uric acid

A nanocomposite is described that consists of TmPO₄ and graphene oxide (GO) and is used to modify a glassy carbon electrode (GCE) to obtain a sensor for simultaneous determination of ascorbic acid (AA), dopamine (DA) and uric acid (UA). GO and TmPO₄ were synthesized via the Hummers method and by a hydrothermal method, respectively. The nanocomposite was characterized by transmission electron microscopy, energy dispersive X-ray spectroscopy, powder X-ray diffraction and Fourier transform infrared spectroscopy. The electrochemical properties of the modified GCE were studied by electrochemical impedance spectroscopy and cyclic voltammetry. The good performance of the modified GCE results from the synergistic effects between GO with its good electrical conductivity and of TmPO₄ as the electron mediator that accelerates the electron transfer rate. Compared to a bare GCE, a GO/GCE and a TmPO₄/GCE, the GO/TmPO₄/GCE exhibits three well-defined and separated oxidation peaks (at -0.05, +0.13 and + 0.26 V vs. SCE). Responses to AA, DA and UA are linear in the 0.1-1.0 mM, 2-20 μM and 10-100 μM concentration ranges, respectively. Graphical abstract Schematic presentation of a nanocomposite that consists TmPO₄ and graphene oxide (GO) and is used to modify a glassy carbon electrode (GCE) to obtain a sensor for simultaneous determination of ascorbic acid (AA), dopamine (DA) and uric acid (UA).

Superlattice stacking by hybridizing layered double hydroxide nanosheets with layers of reduced graphene oxide for electrochemical simultaneous determination of dopamine, uric acid and ascorbic acid

A self-assembled periodic superlattice material was obtained by integrating positively charged semiconductive sheets of a Zn-NiAl layered double hydroxide (LDH) and negatively charged layers of reduced graphene oxide (rGO). The material was used to modify a glassy carbon electrode which then is shown to be a viable sensor for the diagnostic parameters dopamine (DA), uric acid (UA) and ascorbic acid (AA). The modified GCE displays excellent electrocatalytic activity towards these biomolecules. This is assumed to be due to the synergistic effects of (a) excellent interfacial electrical conductivity that is imparted by direct neighboring of conductive rGO to semiconductive channels of LDHs, (b) the superb intercalation feature of LDHs, and (c) the enlarged surface with an enormous number of active sites. The biosensor revealed outstanding electrochemical performances in terms of selectivity, sensitivity, and wide linear ranges. Typically operated at working potentials of -0.10, +0.13 and + 0.27 V vs. saturated calomel electrode, the lower detection limits for AA, DA and UA are 13.5 nM, 0.1 nM, and 0.9 nM, respectively, at a signal-to-noise ratio of 3. The sensor was applied to real-time tracking of dopamine efflux from live human nerve cells. Graphical abstract Schematic of the preparation of a superlattice self-assembled material by integrating positively charged semiconductive sheets of Zn-NiAl layered double hydroxide (LDH) with negatively charged reduced graphene oxide (rGO) layers. It was applied to simultaneous electrochemical detection of dopamine (DA), uric acid and ascorbic acid.