Chan Wei

Nafion covered core–shell structured Fe3O4@graphene nanospheres modified electrode for highly selective detection of dopamine

Nafion covered core-shell structured Fe3O4@graphene nanospheres (GNs) modified glassy carbon electrode (GCE) was successfully prepared and used for selective detection dopamine. Firstly, the characterizations of hydro-thermal synthesized Fe3O4@GNs were investigated by scanning electron microscopy (SEM), transmission electron microscopy (TEM) and Raman spectroscopy. Then Fe3O4@GNs/Nafion modified electrode exhibited excellent electrocatalytic activity toward the oxidations of dopamine (DA). The interference test showed that the coexisted ascorbic acid (AA) and uric acid (UA) had no electrochemical interference toward DA. Under the optimum conditions, the broad linear relationship was obtained in the experimental concentration from 0.020 μM to 130.0 μM with the detection limit (S/N=3) of 0.007 μM. Furthermore, the core-shell structured Fe3O4@GNs/Nafion/GCE was applied to the determination of DA in real samples and satisfactory results were got, which could provide a promising platform to develop excellent biosensor for detecting DA.

A high performance electrochemical biosensor based on Cu2O–carbon dots for selective and sensitive determination of dopamine in human serum

A green and facile method was developed by synthesizing a cuprous oxide–carbon dots/Nafion (Cu2O–CDs/NF) composite film for highly sensitive and reliable determination of dopamine (DA). The Cu2O nanoparticles could improve the conductivity of the electrode, while the CDs with carboxyl groups and the NF with sulfo groups could attract cations via the ion-exchange model and exclude anions by the electrostatic action. The proposed biosensor exhibited a low detection limit of 1.1 nM with a wide linear range of 0.05–45.0 μM and acquired excellent sensitivity and selectivity for DA. Furthermore, the Cu2O–CDs/NF/GCE also was applied to determine DA in human serum with satisfactory results and showed good activity for more than two months.

Fluorescent probes for “off–on” sensitive and selective detection of mercury ions and L-cysteine based on graphitic carbon nitride nanosheets

A novel approach for preparation of graphitic carbon nitride nanosheets (CNNS) from stripping graphitic carbon nitride by strong acid and ultrasonic technology was demonstrated in this study for the first time. Transmission electron microscopy (TEM) was employed to characterize the surface morphology. Atomic force microscope (AFM) was carried out to characterize the thickness of nanosheets. X-Ray diffraction (XRD) was performed to estimate the lattice structure. X-Ray photoelectron spectroscopy (XPS) was carried out to characterize the surface composition and element analysis. Fourier transform infrared spectroscopy (FT-IR) was allowed to identify the functional groups. The as-synthesized CNNS exhibited excellent emission property as well as excitation-independent emission behavior, and fluorescence quantum yields could reach approximately 12.53%. Mercury ion (Hg2+) can make a result of quenching the significant intensity of fluorescence of CNNS by formation of a covalent bond between empty orbital of Hg2+ and the π electrons of N (turn-off). Moreover, the addition of the L-cysteine (L-Cys) can enhance the intensity of fluorescence of the CNNS– Hg2+ system through the thiol group of L-Cys anchored with Hg2+ and drag it from the surface of CNNS (turn-on). The CNNS was consequently functioned as a fluorescence probe towards “off–on” detection of Hg2+ and L-Cys with high sensitivity and selectivity. Moreover, the fluorescent probe was applied to detect tap water and well water with satisfactory results.

Microwave synthesis of 3D rambutan-like CuO and CuO/reduced graphene oxide modified electrodes for non-enzymatic glucose detection

A novel type of cupric oxide (CuO) particles-reduced graphene oxide (r-GO) modified electrode has been fabricated through a facile, simple and fast microwave method. Scanning electron microscopy (SEM), transmission electron microscopy (TEM), Brunauer-Emmett-Teller (BET), and X-ray diffraction (XRD) were employed to characterize the morphologies and structures of the as-prepared samples. The results reveal that the CuO/r-GO composite was a porous 3D rambutan-like microstructure with high surface area. Then the CuO and CuO/r-GO electrodes were constructed for their use as non-enzymatic glucose biosensors owing to their high-performance and sensitivity under alkaline conditions. The proposed biosensor exhibits glucose concentrations in the range from 0.50 μM to 3.75 mM. Besides, chronoamperometry demonstrates a desirable sensitivity of 52.1 μA mM-1 at an applied potential of 0.50 V (vs. Ag/AgCl), with a detection limit of 0.10 μM (signal/noise = 3). Most importantly, this non-enzymatic glucose biosensor has highly stable characteristics and can be manufactured into a long-term stability electrode for its application in various complicated circumstances. All these results confirm that this CuO/r-GO biosensor is a promising active material with excellent analytical properties for non-enzymatic glucose detection.

One step synthesis cadmium sulphide/reduced graphene oxide sandwiched film modified electrode for simultaneous electrochemical determination of hydroquinone, catechol and resorcinol

In this work, a novel sandwiched film of cadmium sulphide/reduced graphene oxide (CdS/r-GO) was synthesized via one step hydro-thermal reaction and electrodes modified with this composite were successfully used to simultaneously determine hydroquinone (HQ), catechol (CC) and resorcinol (RC). Additionally, some kinetic parameters, such as the charge transfer coefficient (α) and the electron transfer rate constant (ks) were calculated. Differential pulse voltammetry (DPV) was used for the simultaneous determination of HQ, CC and RC in their ternary mixture. The calibration curves of HQ, CC and RC were obtained in the ranges of 0.2 to 2300 μM, 0.5 to 1350 μM and 1.0 to 500 μM, respectively. The detection limits for HQ, CC and RC were 0.054 μM, 0.09 μM and 0.23 μM, respectively (S/N = 3). The modified electrode was then used to analyse tap water, well water and river water and the results show its significance for practical applications in the aquatic environment.

Highly sensitive simultaneous electrochemical determination of hydroquinone, catechol and resorcinol based on carbon dot/reduced graphene oxide composite modified electrodes

In this work, a simple and highly sensitive electrochemical method was developed for the simultaneous detection of hydroquinone (HQ), catechol (CC) and resorcinol (RC) based on a carbon dot/reduced graphene oxide composite on a glassy carbon electrode (GCE). The electron communication between reduced graphene oxide (r-GO) and CDs can be further strengthened via hydrogen bonding and π–π stacking forces. The electrochemical behavior of the CD/r-GO/GCE sensor toward HQ, CC and RC was probed by cyclic voltammetry (CV) and differential pulse voltammetry (DPV). The results showed that the calibration curves were in the range of 0.5 to 1000 μM, 1.0 to 950 μM and 5.0 to 600 μM, respectively. The detection limits for HQ, CC and RC were 0.17 μM, 0.28 μM and 1.0 μM (S/N = 3), respectively. Moreover, the sensor has been successfully applied in detecting tap water, river water and industrial sewage.

A nitrogen-doped carbon dot/ferrocene@β-cyclodextrin composite as an enhanced material for sensitive and selective determination of uric acid

A simple and convenient method for the synthesis of nitrogen-doped carbon dots (N-CDs) was reported. Layers of the N-CDs and ferrocene@β-cyclodextrin (Fc@β-CD) host–guest complex were deposited on a glassy carbon electrode (GCE) which was used for highly selective and sensitive detection of uric acid (UA). Under the optimal conditions, compared to bare, N-CD and Fc@β-CD modified electrodes, the Fc@β-CD/N-CD/GCE had higher catalytic activity toward the oxidation of UA. Differential pulse voltammetry (DPV) was used as the analytical technique for detection of UA, the observed linear range for the determination of the UA concentration was from 5 μM to 120 μM with the detection limit estimated to be 0.08 μM (3S/N). Meanwhile, it was applied to determine uric acid in spiked samples with satisfactory results.

Ultrasensitive-electrochemical sensor for the detection of luteolin in Chrysanthemums and Peanut shells using an Au/Pd/reduced graphene oxide nanofilm

In this study, a rapid and ultrasensitive luteolin sensor has been developed based on an Au/Pd/reduced graphene oxide (Au/Pd/rGO) nanofilm modified glassy carbon electrode (GCE). A green and facile method was used for the synthesis of Au/Pd/rGO, in which the groups on GO, for example, hydroxyls, epoxides and carboxyls, are used for the in situ anchoring of Au/Pd bimetallic nanocrystal precursors, which are further reduced to form an Au/Pd/rGO nanofilm. Under optimized conditions, the Au/Pd/rGO/GCE demonstrated a more excellent electrochemical response for the determination of luteolin than GCE, Au/rGO/GCE and Pd/rGO/GCE. This luteolin sensor has a linear range from 0.01 to 80.0 μM and a detection limit of 0.98 nM. In addition, the sensor was also applied to determine luteolin in Chrysanthemums and Peanut shells with satisfactory results. The proposed sensor has good stability for three months.

Microwave-assisted synthesis of carbon dots–zinc oxide/multi-walled carbon nanotubes and their application in electrochemical sensors for the simultaneous determination of hydroquinone and catechol

A facile, efficient, and rapid microwave-assisted synthesis was developed to prepare carbon dots–zinc oxide/multi-walled carbon nanotubes (CDs–ZnO/MWCNTs) composite. The CDs–ZnO/MWCNT material was characterized by scanning electron microscopy (SEM), high-resolution transmission electron microscopy (HRTEM), Fourier transform infrared spectroscopy (FT-IR), and X-ray diffraction (XRD). The electrode modified with the CDs–ZnO/MWCNTs composite was applied for the simultaneous determination of hydroquinone (HQ) and catechol (CC) in 0.1 M phosphate buffer solution (PBS, pH = 4.5). The anodic potential difference (ΔEpa) between HQ and CC was 104 mV, which indicated that the modified electrode could simultaneously detect HQ and CC. The calibration curves for both HQ and CC were obtained in the range from 5.0 to 200 μM, and the detection limits (S/N = 3) were 0.02 μM and 0.04 μM, respectively. The modified electrode was applied to determine HQ and CC in tap water and the recovery rates were 99.3–105.4% for HQ and 104.3–110.1% for CC.