Yonglan Feng

A graphene oxide-based electrochemical sensor for sensitive determination of 4-nitrophenol.

A graphene oxide (GO) film coated glassy carbon electrode (GCE) was fabricated for sensitive determination of 4-nitrophenol (4-NP). The GO-based sensor was characterized by scanning electron microscope, atomic force microscopy and electrochemical impedance spectroscopy. The electrochemical behaviors of 4-NP at the GO-film coated GCE were investigated in detail. In 0.1M acetate buffer with a pH of 4.8, 4-NP yields a very sensitive and well-defined reduction peak at the GO-modified GCE. It is found that the GO film exhibits obvious electrocatalytic activity toward the reduction of 4-NP since it not only increases the reduction peak current but also lowers the reduction overpotential. Based on this, an electrochemical method was proposed for the direct determination of 4-NP. Various kinetic parameters such as transfer electron number, transfer proton number and standard heterogeneous rate constant were calculated, and various experimental parameters were also optimized. Under the optimal conditions, the reduction peak current varies linearly with the concentration of 4-NP ranging from 0.1 to 120 μM, and the detection limit is 0.02 μM at the signal noise ratio of 3. Moreover, the fabricated sensor presented high selectivity and long-term stability. This electrochemical sensor was further applied to determine 4-NP in real water samples, and it showed great promise for simple, sensitive, and quantitative detection of 4-NP.

Green synthesis of silver nanoparticles–graphene oxide nanocomposite and its application in electrochemical sensing oftryptophan

A new kind of nanocomposite based on silver nanoparticles (AgNPs)/graphene oxide (GO) was conveniently achieved through a green and low-cost synthesis approach using glucose as a reducing and stabilizing agent, and the synthetic procedure can be easily used for the construction of a disposable electrochemical sensor on glassy carbon electrode (GCE). The nanocomposite was detailedly characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), energy dispersive X-ray spectroscopy (EDX), Fourier transform infrared spectroscopy (FTIR) and electrochemical impedance spectroscopy (EIS). The experimental results demonstrated that the nanocomposite possessed the specific features of both silver nanoparticles and graphene, and the intrinsic high specific area and the fast electron transfer rate ascribed to the nanohybrid structure could improve its electrocatalytic performance greatly. Cyclic voltammetry (CV) and differential pulse voltammetry (DPV) were employed to evaluate the electrochemical properties of AgNPs/GO/GCE towards tryptophan, and the AgNPs/GO film exhibited a distinctly higher activity for the electro-oxidation of tryptophan than GO film with tenfold enhancement of peak current. The oxidation mechanism and the kinetic parameters were investigated, and analysis operation conditions were optimized. Under the selected experimental conditions, the oxidation peak currents were proportional to tryptophan concentrations over the range of 0.01 μM to 50.0 μM and 50.0 μM to 800.0 μM, respectively. The detection limit was 2.0 nM (S/N=3). Moreover, the proposed method is free of interference from tyrosine and other coexisting species. The resulting sensor displays excellent repeatability and long-term stability; finally it was successfully applied to detect tryptophan in real samples with good recoveries, ranging from 99.0% to 103.0%.

High-sensitivity paracetamol sensor based on Pd/graphene oxide nanocomposite as an enhanced electrochemical sensing platform

Well-dispersed Pd nanoparticles were facilely anchored on graphene oxide (Pd/GO) via a one-pot chemical reduction of the Pd(2+) precursor without any surfactants and templates. The morphology and composition of the Pd/GO nanocomposite were characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), Fourier transform infrared spectroscopy (FTIR) and energy dispersive analysis of X-ray (EDX). The stepwise fabrication process of the Pd/GO modified electrode and its electrochemical sensing performance towards paracetamol was evaluated using electrochemical impedance spectroscopy (EIS), cyclic voltammetry (CV) and differential pulse voltammetry (DPV). The experimental results indicate that the as-synthesized Pd nanoparticles are relatively uniform in size (5-10 nm) without large aggregation and uniformly distributed in the carbon matrix with the overall Pd content of 28.77 wt% in Pd/GO. Compared with the GO modified electrode, the Pd/GO modified electrode shows a better electrocatalytic activity to the oxidation of paracetamol with lower oxidation potential and larger peak current, so the Pd/GO nanocomposite can be used as an enhanced sensing platform for the electrochemical determination of paracetamol. The kinetic parameters of the paracetamol electro-oxidation at Pd/GO electrode were studied in detail, and the determination conditions were optimized. Under the optimal conditions, the oxidation peak current is linear to the paracetamol concentration in the ranges of 0.005-0.5 μM and 0.5-80.0 μM with a detection limit of 2.2 nM. Based on the high sensitivity and good selectivity of the Pd/GO modified electrode, the proposed method was successfully applied to the determination of paracetamol in commercial tablets and human urines, and the satisfactory results confirm the applicability of this sensor in practical analysis.

Acetylene black paste electrode modified with graphene as the voltammetric sensor for selective determination of tryptophan in the presence of high concentrations of tyrosine

A reliable sensor was fabricated by modifying an acetylene black paste electrode with graphene (denoted as GR/ABPE) for sensitive and selective determination of tryptophan (Trp). Due to the high sorption ability, large surface area and numerous active sites, the GR/ABPE showed a strong enhancement effect on the oxidation of Trp, and greatly increased the peak current. The parameters affecting the Trp determination were investigated. In 1.0 M H2SO4 the voltammetric responses of Trp and tyrosine (Tyr) were well separated into two distinct peaks with peak potential difference (ΔE(pa)) of 115 mV. Under the optimized conditions, in the presence of 0.1 mM Tyr, the oxidation peak current of Trp was proportional to its concentration in the range between 0.1 μM and 0.1 mM, with the limit of detection of 60 nM (S/N=3). The GR/ABPE was applied to the direct detection of Trp in pharmaceutical and biological samples with satisfactory results. This work provides a simple and easy approach to selective detection of Trp in the presence of Tyr.

Sensitive determination of bisphenol A in plastic products by derivative voltammetry using an acetylene black paste electrode coated with salicylaldehyde-modified chitosan

A sensitive and reliable electrochemical method was developed for determination of bisphenol A (BPA) in plastic products using an acetylene black paste electrode coated with salicylaldehyde-modified chitosan (denoted as S-CHIT/ABPE). In the second-order derivative linear sweep voltammetry technique, BPA yielded a very sensitive and well-defined oxidation peak at 842 mV in 0.2 mol L−1 HCl solution. Owing to its unique structure and extraordinary properties, S-CHIT/ABPE showed higher accumulation efficiency toward BPA compared with bare ABPE, and significantly enhanced the oxidation peak current of BPA. Under the optimum conditions, the oxidation peak current was proportional to the concentration of BPA over the range of 4.0 × 10−8 mol L−1 ∼ 1.0 × 10−5 mol L−1. The detection limit (S/N = 3) was 2.0 × 10−8 mol L−1. The fabricated S-CHIT/ABPE not only exhibited strong adsorption capacity toward BPA, but also provided remarkable stable and quantitatively reproducible analytical performance. Additionally, this newly-developed method possesses some obvious advantages including high sensitivity, extreme simplicity, rapid response and low cost.

One-pot in situ synthesis of a CoFe2O4 nanoparticle-reduced graphene oxide nanocomposite with high performance for levodopa sensing

In this work, a simple and facile protocol for the synthesis of a cobalt-ferrite magnetic nanoparticle-reduced graphene oxide nanocomposite (CoFe2O4/RGO) was achieved using an in situ chemical co-precipitation method. The characteristics of the synthesized nanocomposite were carefully investigated by scanning electron microscopy, energy dispersive X-ray spectroscopy, X-ray powder diffraction, Fourier transform infrared spectroscopy and electrochemical technologies, respectively. The results reveal that the abundant CoFe2O4 nanoparticles are successfully formed with particle sizes in the range of 460–510 nm and uniformly anchored on the RGO nanosheets. Due to the imbedding of CoFe2O4 nanoparticles, the nanocomposite exhibits a larger surface area and superior electrocatalytic activity towards the oxidation of levodopa, which could be used as an efficient electrocatalyst for levodopa sensing. The parameters that influence the sensing property were investigated in detailed. Under the optimum conditions, the oxidation peak currents obtained by differential pulse voltammetry and chronoamperometry show linear responses for levodopa concentrations in the ranges of 0.02–45 μM and 10–420 μM respectively, and a low detection limit of 12 nM is achieved. Compared with those of the existing analogues reported for levodopa detection, the CoFe2O4/RGO-based sensor demonstrates outstanding properties such as high sensitivity, low detection limit and wide linear dynamic range. Finally, the practical analytical application of the developed sensor was assessed by the determination of levodopa in commercially available tablets and urine samples, and satisfactory recoveries were obtained in the range of 97.8–103.2%.

Syntheses, Crystal Structures and Biological Activity of the 1D Chain Benzyltin Complexes Based on 2-Oxo-Propionic Acid Benzoyl Hydrazone

Two new 1D Chain benzyltin complexes {[C6H4(O)C=N–N=C(Me)COO](CH3OH)(C6H5CH2)2Sn}n (1), {[C6H4(O)C–NH–N=C(Me)COO](C6H5CH2)3Sn}n (2) were synthesized by the reactions of 2-oxo-propionic acid benzoyl hydrazone with dibenzyltin dichloride or tribenzyltin chloride, respectively. The two complexes were characterized by FT-IR, 1H, 13C and 119Sn NMR spectra, elemental analysis, X-ray single crystal diffraction and TGA. In vitro antitumor activities of both complexes were evaluated by the 3-(4,5-dimethylthiazoly-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assay against three human cancer cell lines (NCI-H460, HepG2, MCF7) and human cell line (HL7702). The 1 exhibited strong antitumor activity than 2, then it was expected after further chemical optimization of candidate compounds as anti-cancer drugs. The interaction between complexes and calf thymus DNA were studied by EB fluorescent probe, the interaction of 1 and 2 with calf thymus DNA were intercalation and electrostatic attraction.

An enhanced electrochemical sensing platform integrated with graphene oxide and iron hydroxide colloid for sensitive determination of phloroglucinol

A novel electrochemical sensing platform was fabricated with nanohybrid consisting of graphene oxide and iron hydroxide colloid. With high surface area and excellent electrical conductivity of the nanohybrid, the prepared electrochemical sensor exhibited preeminent electrocatalytic activity towards the oxidation of phloroglucinol, resulting in the increase of the oxidation peak current and decrease of the oxidation overpotential. The nanohybrid was used as an enhanced electrochemical sensing platform for sensitive determination of phloroglucinol. The oxidation mechanism of phloroglucinol at this sensing platform was investigated in detail, the determination conditions were optimized, and the kinetic parameters were also calculated. Under the optimized conditions, the oxidation peak current was proportional to phloroglucinol concentration in the range from 5.00 to 100.00 nmol L-1 with limits of detection and of quantification of 3.45 and 11.51 nmol L-1, respectively. This sensing platform displayed long-term stability, high reproducibility and super anti-interference capability. It was employed to detect phloroglucinol in environmental water samples with good recoveries. The excellent performance, operational simplicity and low expense make the graphene-based hybrid attractive in the sensor construction.

Preparation of L-Tryptophan Electrochemical Sensor Based on Graphene Oxide/Carbon Nanotubes Nanocomposite Modified Electrode

A single-layer graphene oxide(GO) was prepared by Hummers method,and then mixed with multiwalled carbon nanotubes(MWCNT) in ultrasound bath to form stable GO/MWCNT nanocomposites.A novel L-tryptophan(L-Trp) electrochemical sensor was fabricated based on GO/MWCNT modified glassy carbon electrode.The modified electrode was characterized by transmission electron microscope(TEM),cyclic voltammetry(CV) and alternating current impedance(EIS),and the electrochemical behaviors and kinetic properties of L-Trp on the modified electrode were also investigated.The experimental results showed that a sensitive oxidation peak of L-Trp appeared at GO/MWCNT modified electrode(Epa=0.956 V),and the oxidation reaction was an irreversible process containing two electrons and two protons transfer.This electrode process controlled by the adsorption step,and the standard rate constant was 9.613×10-6 cm/s.Trace levels of L-Trp can be determined by this oxidation peak.In phosphate buffer of pH 6.0,the oxidation peak currents were linearly dependent on the L-Trp concentrations in the range of 1.00×10-6-1.00×10-4 mol/L with accumulation time of 25 s at 0.600 V and scan rate of 100 mV/s.The correlation coefficient was 0.995 and the detection limit was 3.50×10-7 mol/L.The prepared electrochemical sensor had favorable stability and could be applied to the quick determination of L-Trp in human serum,and the recovery of standard addition was from 97.8% to 104.2%.