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An effective nanocomposite sensor for selective electroanalytical dopamine (DA) determination using overoxidized conducting polymer of poly‐1,5‐diaminonaphthalene (OPoly‐1,5‐DAN) functionalized graphene nanosheets (GNS) was achieved. The OPoly‐1,5‐DAN/GNS nanocomposite polymer was prepared via an electropolymerization of 1,5‐DAN on GNS/GCE after 7 cycles of potential scan (−0.2 V to +0.9 V), followed by an electrooveroxidation of the nanocomposite Poly‐1,5‐DAN/GNS by the potential cycle (0.0 V to +1.8 V) for 2 scans. The OPoly‐1,5‐DAN was effectively designed by GNS as a uniformly distribution of nanocomposite that caused more accumulations of analyte due to large electrocatalytic active positions created on electrode surface. The high specific and sensitive performance of the OPoly‐1,5‐DAN/GNS nanocomposite polymer was conducted to greater effective electrons transferring behavior for DA with copresent of vitamin C (VC). The stable and suitable formation of OPoly‐1,5‐DAN/GNS nanocomposite polymer showed rapid charge transport voltammogram and obvious electrocatalytic activity to DA and eliminated VC response. Moreover, the OPoly‐1,5‐DAN/GNS displays an excellent responses to DA determination with wide linear range (LR) 1.0–150 μM and lower detection limit (DL) 8.82±0.1 nM as comparing with other studies. Additionally, the excellent reproducibility of OPoly‐1,5‐DAN/GNS as well as long‐term stability indicated that it is an excellent and effective electrochemical DA sensor. Finally, the electroanalytical application of the OPoly‐1,5‐DAN/GNS nanocomposite polymer was employed for the electroanalysis of DA in human urine. [ABSTRACT FROM AUTHOR]

Abstract: Active electrocatalytic electrode designs are needed for the sensitive and selective detection of a single or multi-active biomolecule among biological components. We report the design of hierarchical NiO catalyst (HNC) for one-step monitoring of bioactive molecules such as ascorbic acid (AA), dopamine (DA), and uric acid (UA). The novel mesostructured geometries, active surface sites, and multi-diffused spaces for easy electron movement through gaps provide highly active electrocatalytic electrode designing surface. Controlled HNC architecture along electrode-design surface domains having double-head branches spread out along both sides of the dipole-like rod may lead to the vital electron transfer and fast response signaling of multi-bioactive molecules in one-shot triggering individually or simultaneously. Electrochemical analyses showed evidence that the proposed electrode design can detect each component up to 0.02 µM. Sensitive detection up to 1.127, 0.02, and 0.978 µM and wide-range responses of 25-800, 2-60, and 10-000 µM for AA, DA, and UA, respectively, were observed. The simultaneous monitoring and selective signaling of AA, DA, and UA in real urine samples in one step under different potentials were realized. Thus, the HNC-modified electrode can monitor and evaluate the coexistence of biomolecules simultaneously in multi-components.Graphical Abstract: The electrochemical oxidation of AA, DA, and UA at the HNC-modified electrode and the corresponding DPV peaks with losing of 2e−/2H+. [ABSTRACT FROM AUTHOR]

An electrochemical sensor for the simultaneous determination of ascorbic acid (AA), dopamine (DA), uric acid (UA) and folic acid (FA) using gold nanoclusters (AuNCs)/activated graphene (AGR)/MWCNT nanocomposite was fabricated. The AGR/MWCNT nanocomposite was prepared via the electrochemical reduction of GR/MWCNT while AuNCs were formed onto the AGR/MWCNT film through the electrodeposition of Au. The AuNCs/AGR/MWCNT nanocomposite was characterized using different techniques, such as scanning electron microscopy (SEM), electrochemical impedance spectroscopy (EIS), X-ray photoelectron spectroscopy (XPS) and cyclic voltammetry (CV). The nanocomposite sensor exhibited sharp and obvious peaks for the oxidation of AA, DA, UA and FA as compared to a bare electrode. The AuNCs/AGR/MWCNT probe displays an efficient electron mediating behavior with well separated oxidation peak potentials between AA to DA, DA to UA and UA to FA were 0.21, 0.14 and 0.28 V, respectively. The linear calibration curves of AA, DA, UA and FA were observed from 10–150 μM, 1.0–210 μM, 5.0–100 μM and 10–170 μM with detection limits of 0.27 ± 0.1 μM, 0.08 ± 0.02 μM, 0.10 ± 0.03 μM and 0.09 ± 0.01 μM, respectively. In addition, the analytical application of the proposed sensor was successfully conducted for the determination of these species in human urine real samples. [ABSTRACT FROM AUTHOR]

• A novel nanocomposite based on the (Au/Ag/Pd)NPs/EPGr was fabricated. • The nanocomposite was applied for the simultaneous determination for AA, DA, AP and TP. • A high sensitive and large separation peak potentials for AA–DA, DA–AP, and AP–TP were observed. • The low limits of detection for AA, DA, AP and TP were estimated as compared to other reports. • The nanocomposite successfully applied for the determination of these species in real sample. A novel nanocomposite sensor based on trimetallic nanoparticles of (Au/Ag/Pd)NPs uniformly capped electropretreated graphene oxide (EPGrO) was fabricated. The investigation and characterization of the (Au/Ag/Pd)NPs/EPGrO nanocomposite were studied by X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD) and energy-dispersive X-ray spectroscopy (EDX) techniques. Cyclic voltammograms (CVs) of the nanocomposite electrode displayed obvious and sharp oxidation peaks for each ascorbic acid (AA), dopamine (DA), acetaminophen (AP) and tryptophan (TP) as compared to their responses at EPGrO and bare electrodes. An efficient electron mediating behavior of the nanocomposite electrode with large separation peak potentials for AA–DA, DA–AP, and AP–TP were estimated to be 0.16, 0.18 and 0.29 V, respectively. In addition, differential pulse voltammograms (DPVs) of the nanocompsite electrode showed simultaneous determination of AA, DA, AP and TP with linear calibration plots from 5–650 μM, 1–700 μM, 5–700 μM and 1–600 μM where their detection limits were calculated to be 0.24 ± 0.03, 0.02 ± 0.01, 0.12 ± 0.04 and 0.03 ± 0.01 μM, respectively. Finally, the practical application of the (Au/Ag/Pd)NPs/EPGrO nanocomposite electrode was successfully conducted for the analytical determination of AA, DA, AP and TP in real sample of human blood serum. [ABSTRACT FROM AUTHOR]