Zhenfan Sun

Direct electrochemistry with enhanced electrocatalytic activity of hemoglobin in hybrid modified electrodes composed of graphene and multi-walled carbon nanotubes

A graphene (GR) and multi-walled carbon nanotubes (MWCNT) hybrid was prepared and modified on a 1-hexylpyridinium hexafluorophosphate based carbon ionic liquid electrode (CILE). Hemoglobin (Hb) was immobilized on GR-MWCNT/CILE surface with Nafion as the film forming material and the modified electrode was denoted as Nafion/Hb-GR-MWCNT/CILE. Spectroscopic results revealed that Hb molecules retained its native structure in the GR-MWCNT hybird. Electrochemical behaviors of Hb were carefully investigated by cyclic voltammetry with a pair of well-defined redox peaks obtained, which indicated that direct electron transfer of Hb was realized in the hybrid modified electrode. The result could be attributed to the synergistic effects of GR-MWCNT hybrid with enlarged surface area and improved conductivity through the formation of a three-dimensional network. Electrochemical parameters of the immobilized Hb on the electrode surface were further calculated with the results of the electron transfer number (n) as 1.03, the charge transfer coefficient (a) as 0.58 and the electron-transfer rate constant (ks) as 0.97 s(-1). The Hb modified electrode showed good electrocatalytic ability toward the reduction of different substrates such as trichloroacetic acid in the concentration range from 0.05 to 38.0 mmol L(-1) with a detection limit of 0.0153 mmol L(-1) (3σ), H2O2 in the concentration range from 0.1 to 516.0 mmol L(-1) with a detection limit of 34.9 nmol/L (3σ) and NaNO2 in the concentration range from 0.5 to 650.0 mmol L(-1) with a detection limit of 0.282 μmol L(-1) (3σ). So the proposed electrode had the potential application in the third-generation electrochemical biosensors without mediator.

Electrochemical deoxyribonucleic acid biosensor based on carboxyl functionalized graphene oxide and poly-l-lysine modified electrode for the detection of tlh gene sequence related to vibrio parahaemolyticus

A carboxyl functionalized graphene oxide (GO-COOH) and electropolymerized poly-l-lysine (PLLy) modified glassy carbon electrode (GCE) was fabricated and used for the construction of an electrochemical deoxyribonucleic acid (DNA) biosensor. The NH(2) modified probe ssDNA sequences were immobilized on the surface of GO-COOH/PLLy/GCE by covalent linking with the formation of amide bonds, which was stable and further hybridized with the target ssDNA sequence. Differential pulse voltammetry (DPV) was used to monitor the hybridization events with methylene blue as electrochemical indicator, which gave a sensitive reduction peak at -0.287 V (vs. SCE). Under the optimal conditions the reduction peak current was proportional to the concentration of tlh gene sequence in the range from 1.0×10(-12) to 1.0×10(-6) mol L(-1) with a detection limit as 1.69×10(-13) mol L(-1) (3σ). The polymerase chain reaction products of tlh gene from oyster samples were detected with satisfactory results, indicating the potential application of this electrochemical DNA sensor.

Direct electrochemistry of hemoglobin on graphene and titanium dioxide nanorods composite modified electrode and itselectrocatalysis

A biocompatible sensing platform based on graphene (GR) and titanium dioxide (TiO₂) nanorods for the immobilization of hemoglobin (Hb) was adopted in this paper. The GR-TiO₂-Hb composite-modified carbon ionic liquid electrode was constructed through a simple casting method with Nafion as the film forming material. UV-Vis and FT-IR spectra confirmed that Hb retained its native structure in the composite film. Direct electron transfer of Hb incorporated into the composite was realized with a pair of quasi-reversible redox waves appeared, indicating that the presence of GR-TiO₂ nanocomposite on the electrode surface could facilitate the electron transfer rate between the electroactive center of Hb and the substrate electrode. Hb modified electrode showed excellent electrocatalytic activity to the reduction of trichloroacetic acid in the concentration range from 0.6 to 21.0 mmol L⁻¹. These results indicated that GR-TiO₂ nanocomposite could be a friendly biocompatible interface for immobilizing biomolecules and keeping their native structure. The fabricated biosensor displayed the advantages such as high sensitivity, good reproducibility and long-term stability.

Poly(methylene blue) functionalized graphene modified carbon ionic liquid electrode for the electrochemical detection of dopamine.

An ionic liquid 1-butylpyridinium hexafluorophosphate based carbon ionic liquid electrode (CILE) was used as the substrate electrode and a poly(methylene blue) (PMB) functionalized graphene (GR) composite film was co-electrodeposited on CILE surface by cyclic voltammetry. The PMB-GR/CILE exhibited better electrochemical performances with higher conductivity and lower electron transfer resistance. Electrochemical behavior of dopamine (DA) was further investigated by cyclic voltammetry and a pair of well-defined redox peaks appeared with the peak-to-peak separation (ΔE(p)) as 0.058V in 0.1 mol L(-1) pH 6.0 phosphate buffer solution, which proved a fast quasi-reversible electron transfer process on the modified electrode. Electrochemical parameters of DA on PMB-GR/CILE were calculated with the electron transfer number as 1.83, the charge transfer coefficients as 0.70, the apparent heterogeneous electron transfer rate constant as 1.72 s(-1) and the diffusional coefficient (D) as 3.45×10(-4) cm(2) s(-1), respectively. Under the optimal conditions with differential pulse voltammetric measurement, the linear relationship between the oxidation peak current of DA and its concentration was obtained in the range from 0.02 to 800.0 μmol L(-1) with the detection limit as 5.6 nmol L(-1) (3σ). The coexisting substances exhibited no interference and PMB-GR/CILE was applied to the detection of DA injection samples and human urine samples with satisfactory results.

Fabrication of graphene-platinum nanocomposite for the direct electrochemistry and electrocatalysis of myoglobin

In this paper a platinum (Pt) nanoparticle decorated graphene (GR) nanosheet was synthesized and used for the investigation on direct electrochemistry of myoglobin (Mb). By integrating GR-Pt nanocomposite with Mb on the surface of carbon ionic liquid electrode (CILE), a new electrochemical biosensor was fabricated. UV-Vis absorption and FT-IR spectra indicated that Mb remained its native structure in the nanocomposite film. Electrochemical behaviors of Nafion/Mb-GR-Pt/CILE were investigated with a pair of well-defined redox peak appeared, which indicated that direct electron transfer of Mb was realized on the underlying electrode with the usage of the GR-Pt nanocomposite. The fabricated electrode showed good electrocatalytic activity to the reduction of trichloroacetic acid in the linear range from 0.9 to 9.0 mmol/L with the detection limit as 0.32 mmol/L (3σ), which showed potential application for fabricating novel electrochemical biosensors and bioelectronic devices.

Simultaneous electrochemical determination of guanosine and adenosine with graphene–ZrO2 nanocomposite modified carbon ionic liquid electrode

In this paper an ionic liquid 1-hexylpyridinium hexafluorophosphate based carbon ionic liquid electrode (CILE) was fabricated and used as the basal electrode, which was further modified by graphene (GR) and ZrO2 nanoparticle with chitosan (CTS) film to immobilize the nanocomposite. The modified electrode was denoted as CTS-GR-ZrO2/CILE and further used for the simultaneous detection of adenosine and guanosine. Electrochemical performances of the modified electrode were greatly enhanced due to the presence of GR-ZrO2 nanocomposite, and the direct electro-oxidation behaviors of adenosine and guanosine were carefully investigated. Both adenosine and guanosine exhibited an increase of the oxidation peak currents with the negative shift of the oxidation peak potentials on the modified electrode, which indicated the electrocatalytic activity of GR-ZrO2 nanocomposite on the electrode surface. Electrochemical parameters of adenosine and guanosine on CTS-GR-ZrO2/CILE were calculated respectively, and a new electroanalytical method for the simultaneous determination of adenosine and guanosine was further established with the peak-to-peak separation (ΔEp) as 0.225V. The proposed method was successfully applied to detect adenosine and guanosine in human urine samples with satisfactory results.

Molecular dynamics simulation of diffusion and structure of some n-alkanes in near critical and supercritical carbon dioxide at infinite dilution.

The diffusion coefficients of n-alkanes (from CH4 to C14H30) in near critical and supercritical carbon dioxide at infinite dilution have been studied by molecular dynamics simulation. The simulation results agree well with experiment, which suggests that the simulation method is a powerful tool to obtain diffusion coefficients of solutes in fluids at high pressures. The local structures of such fluids are further investigated by calculating radial distribution functions and coordination numbers. Meanwhile, the dihedral, end-to-end distance and radius of gyration, which are calculated to characterize the flexibility of n-alkanes, are used to reasonably explain the abnormal trends on radial distribution functions and coordination numbers. Moreover, it is found that the flexibility effects on diffusion in pure n-alkanes and infinitely dilute n-alkane/CO2 system are different. The differences in MD simulation results of molecular diffusion in such systems could be qualitatively explained by the flexibility.

Electrodeposited Graphene and Gold Nanoparticle Modified Carbon Ionic Liquid Electrode for Sensitive Detection of Rutin

Abstract A carbon ionic liquid electrode (CILE) was prepared by using ionic liquid 1-hexylpyridinium hexafluorophosphate (HPPF 6 ) as the binder and the modifier, which was further decorated with gold nanoparticles and graphene (GR) through step by step electrochemical method to get a modified electrode denoted as GR/Au/CILE. Electrochemical performance of GR/Au/CILE was greatly enhanced due to the presence of nano-gold and GR. Different electrochemical methods such as cyclic voltammetry, differential pulse voltammetry and chronocoulometry were used to investigate the electrochemical behaviors of rutin on GR/Au/CILE along with the electrochemical parameters calculated. Under the optimal conditions the oxidation peak current of rutin was proportional to its concentration in the range from 8.0 × 10 −8 M to 8.0 × 10 −5 M with the detection limit of 2.55 × 10 −8 M (3σ). The proposed method was further applied to the rutin tablet samples detection with satisfactory results.

The self-diffusion and hydrogen bond interaction in neat liquid alkanols: a molecular dynamic simulation study

Self-diffusion of methanol, ethanol, 1-propanol and 2-propanol has been studied by molecular dynamics simulation in the temperature range between the melting pressure curve and 478 K at pressures up to 300 MPa. The simulation results on self-diffusion of methanol, ethanol and 2-propanol (for 2-propanol, at high temperatures) agree well with experiment, which suggests that the simulation method is a powerful tool to obtain self-diffusion coefficients over wide range of temperature and pressure, under which it is rather difficult for experiments. The local structures of methanol, ethanol and 2-propanol are investigated by calculating the radial distribution functions, H-bond numbers, coordination numbers and the ratios of H-bond number divided by coordination number. The correlation between self-diffusion and structural properties, and the influence of temperature and pressure on them are discussed. The degree of forming H-bond space network in methanol, ethanol and water is higher than that in 2-propanol, and they are all higher than those in ammonia and methylamine. The simulation results demonstrate that the effect of hydrogen bonding on the translational dynamics in methanol and ethanol is more pronounced than that in 2-propanol.