Hanqiang Zhang

A sensitive and reliable dopamine biosensor was developed based on the Au@carbon dots-chitosan composite film

A novel composite film of Au@carbon dots (Au@CDs)-chitosan (CS) modified glassy carbon electrode (Au@CDs-CS/GCE) was prepared in a simple manner and applied in the sensitive and reliable determination of dopamine (DA). The CDs had carboxyl groups with negative charge, which not only gave it have good stability but also enabled interaction with amine functional groups in DA through electrostatic interaction to multiply recognize DA with high specificity, and the Au nanoparticle could make the surface of the electrode more conductive. Compared with the bare GCE, CS/GCE, and CDs-CS/GCE electrodes, the Au@CDs-CS/GCE had higher catalytic activity toward the oxidation of DA. Furthermore, Au@CDs-CS/GCE exhibited good ability to suppress the background current from large excess ascorbic acid (AA) and uric acid (UA). Under the optimal conditions, selective detection of DA in a linear concentration range of 0.01-100.0 μM was obtained with the limit of 0.001 μM (3S/N). At the same time, the Au@CDs-CS/GCE was also applied to the detection of DA content in DAs injection with satisfactory results, and the biosensor could keep its activity for at least 2 weeks.

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.

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.

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.

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.