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).

Gold nanoparticles anchored onto three-dimensional graphene: simultaneous voltammetric determination of dopamine and uric acid.

An electrochemical sensor is described for simultaneous voltammetric determination of dopamine (DA) and uric acid (UA). It is based on the use of a nanomaterial composed of gold nanoparticles and 3-dimensional graphene (Au NP@3D GR). The 3D GR was prepared by chemical vapor deposition using nickel nanoparticles as the template at a temperature of around 900 °C. The surface of 3D GR contains oxygen-functional groups after treatment with acid. Carboxylated Au NP were self-assembled and anchored onto the surface of 3D GR. The nanomaterial was placed on a ITO electrode. The few-layer graphene on the ITO glass has a porous structure and the distribution of Au NP is uniform. The electrode shows a high sensitivity and a low detection limit for DA and UA. Figures of merit include detection limits of 0.1 M for DA and of 0.1 µM for UA, and well separated peaks at potentials of 0.18 and 0.30 V (vs. Ag/AgCl), respectively, at pH 7.0. The electrode has good repeatability and stability. Graphical abstract Carboxylated gold nanoparticles were self-assembled and immobilized on 3-dimensional graphene by chemical vapor deposition for simultaneous determination of dopamine (DA) and uric acid (UA).

Highly sensitive and selective uric acid biosensor based on a three-dimensional graphene foam/indium tin oxide glass electrode.

A three-dimensional (3D) continuous and interconnected network graphene foam (GF) was synthesized by chemical vapor deposition using nickel foam as a template. The morphologies of the GF were observed by scanning electron microscopy. X-ray diffraction and Raman spectroscopy were used to investigate the structure of GF. The graphene with few layers and defect free was closely coated on the backbone of the 3D nickel foam. After etching nickel, the GF was transferred onto indium tin oxide (ITO) glass, which acted as an electrode to detect uric acid using cyclic voltammetry (CV) and differential pulse voltammetry (DPV). The GF/ITO electrode showed a high sensitivity for the detection of uric acid: approximately 9.44 mA mM(-1) in the range of 25 nM-0.1 µM and 1.85 mA mM(-1) in the range of 0.1-60 µM. The limit of detection of GF/ITO electrode for uric acid is 3 nM. The GF/ITO electrode also showed a high selectivity for the detection of uric acid in the presence of ascorbic acid. This electrode will have a wide range of potential application prospects in electrochemical detection.

Highly sensitive and selective dopamine biosensor using Au nanoparticles-ZnO nanocone arrays/graphene foam electrode.

Based on the Au nanoparticles-ZnO nanocone arrays/graphene foam electrode, a novel dopamine biosensor was successfully developed. Graphene foam was synthesized by chemical vapor deposition, ZnO nanocone arrays were grown on its surface by a hydrothermal method and Au nanoparticles with carboxyl groups were self-assembled onto the ZnO nanocone arrays to obtain Au nanoparticles-ZnO nanocone arrays/graphene foam electrode. The result indicates that the prepared electrode has a high sensitivity (4.36 µA µM-1) and low limit of detection (0.04 µM, S/N = 3) for the detection of dopamine. The prepared electrode also exhibits an excellent selectivity under the interference of uric acid, good repeatability and stability. The prepared sensor has been successfully applied in real samples and has a great potential to be used in the field of medical and health.

Synthesis of ZnO nanowire arrays/3D graphene foam and application for determination of levodopa in the presence of uric acid.

Three-dimensional (3D) graphene foam (GF) was prepared by chemical vapor deposition (CVD) using nickel foam as the template. ZnO nanowire arrays (ZnO NWAs) were vertically grown on the 3D GF by hydrothermal synthesis to prepare ZnO NWAs/GF. This hybrid combines the properties of ZnO NWAs and 3D GF, which has favorable electrocatalysis and outstanding electrical conductivity. The vertically aligned ZnO NWAs grown on the GF enlarged the electroactive surface area, which was investigated from the Fe(CN)63-4+ redox kinetic study. The ZnO NWAs/GF was used as an electrochemical electrode for the determination of Levodopa (LD) in the presence of uric acid (UA). The electrochemical responses of the ZnO NWAs/GF electrode were investigated by cyclic voltammetry (CV) and differential pulse voltammetry (DPV). The results show that the sensitivity of the electrode for LD is 3.15µAµM-1 in the concentration range of 0.05-20µM and the measured detection limit of the electrode for LD is 50nM. The electrode also shows good selectivity, reproducibility and stability. The proposed electrode is succsefully used to determine LD in human plasma samples and it is potential for use in clinical research.

ZnO nanowire arrays on 3D hierachical graphene foam: biomarker detection of Parkinson's disease.

We report that vertically aligned ZnO nanowire arrays (ZnO NWAs) were fabricated on 3D graphene foam (GF) and used to selectively detect uric acid (UA), dopamine (DA), and ascorbic acid (AA) by a differential pulse voltammetry method. The optimized ZnO NWA/GF electrode provided a high surface area and high selectivity with a detection limit of 1 nM for UA and DA. The high selectivity in the oxidation potential was explained by the gap difference between the lowest unoccupied and highest occupied molecular orbitals of a biomolecule for a set of given electrodes. This method was further used to detect UA levels in the serum of patients with Parkinson's disease (PD). The UA level was 25% lower in PD patients than in healthy individuals. This finding strongly implies that UA can be used as a biomarker for PD.