Weifeng Li

Core-shell structured Ag@C for direct electrochemistry and hydrogen peroxide biosensor applications

Ag@C core-shell nano-composites have been prepared by a simple one-step hydrothermal method and are further explored for protein immobilization and bio-sensing. The electrochemical behavior of immobilized horseradish peroxidase (HRP) on Ag@C modified indium-tin-oxide (ITO) electrode and its application as H₂O₂ sensor are investigated. Electrochemical and UV-vis spectroscopic measurements demonstrated that Ag@C nano-composites provide excellent matrixes for the adsorption of HRP and the entrapped HRP retains its bioactivities. It is found that on the HRP-Ag@C/ITO electrode, HRP exhibited a fast electron transfer process and good electrocatalytic reduction toward H₂O₂. Under optimum experimental conditions the biosensor linearly responds to H₂O₂ concentration in the range of 5.0×10⁻⁷-1.4×10⁻⁴ M with a detection limit of 2.0×10⁻⁷ M (S/N=3). The apparent Michaelis-Menten constant (K(app)(M)) of the biosensor is calculated to be 3.75×10⁻⁵ M, suggesting high enzymatic activity and affinity toward H₂O₂. In addition, the HRP-Ag@C/ITO bio-electrode shows good reproducibility and long-term stability. Thus, the core-shell structured Ag@C is an attractive material for application in the fabrication of biosensors due to its direct electrochemistry and functionalized surface for efficient immobilization of bio-molecules.

Sensitive electrochemical sensor of tryptophan based on Ag@C core-shell nanocomposite modified glassy carbon electrode.

We here reported a simple electrochemical method for the detection of tryptophan (Trp) based on the Ag@C modified glassy carbon (Ag@C/GC) electrode. The Ag@C core-shell structured nanoparticles were synthesized using one-pot hydrothermal method and characterized by scanning electron microscope (SEM), transmission electron microscope (TEM), and Fourier transform-infrared spectroscopy (FTIR). The electrochemical behaviors of Trp on Ag@C/GC electrode were investigated and exhibited a direct electrochemical process. The favorable electrochemical properties of Ag@C/GC electrode were attributed to the synergistic effect of the Ag core and carbon shell. The carbon shell cannot only protect Ag core but also contribute to the enhanced substrate accessibility and Trp-substrate interactions, while nano-Ag core can display good electrocatalytic activity to Trp at the same time. Under the optimum experimental conditions the oxidation peak current was linearly dependent on the Trp concentration in the range of 1.0×10(-7) to 1.0×10(-4) M with a detection limit of 4.0×10(-8) M (S/N=3). In addition, the proposed electrode was applied for the determination of Trp concentration in real samples and satisfactory results were obtained. The technique offers enhanced sensitivity and may trigger the possibilities of the Ag@C nanocomposite towards diverse applications in biosensor and electroanalysis.

Electrochemical determination of tryptophan based on Si-doped nano-TiO2 modified glassy carbon electrode

An electrochemical sensor was prepared using a glassy carbon electrode modified with Si-doped nano-TiO2 (TS/GC) for the detection of tryptophan (Trp). The electrochemical behavior of Trp at the TS/GC electrode was investigated by cyclic voltammetry (CV). It was found that the anodic peak current of Trp oxidation at the TS/GC electrode was higher than that at the bare electrode or TiO2 nanoparticles modified GC (T/GC) electrode. This finding suggested the enhanced electrochemical properties of the TS/GC electrode, and the improvement of the electrochemical properties was attributed to the presence of oxygen functional groups on the surface of the TS and the easy transfer of electrons and holes. Thereby, the TS/GC electrode was employed to determine Trp and the effects of scan rate, pH and interferents on the response of Trp oxidation were examined. Under the optimum experimental conditions the TS/GC electrode displayed a good analytical performance. The oxidation peak current of Trp showed a linear relationship with concentration over the range of 1.0 × 10−6 to 4.0 × 10−4 M, and the detection limit was estimated to be 5.0 × 10−7 M (S/N = 3). The proposed method was simple and exhibited favorable resistance against interferences. Moreover, the electrochemical sensor was successfully employed to determine Trp in pharmaceutical samples.

A sensitive glucose biosensor based on Ag@C core–shell matrix

Nano-Ag particles were coated with colloidal carbon (Ag@C) to improve its biocompatibility and chemical stability for the preparation of biosensor. The core-shell structure was evidenced by transmission electron microscope (TEM) and the Fourier transfer infrared (FTIR) spectra revealed that the carbon shell is rich of function groups such as -OH and -COOH. The as-prepared Ag@C core-shell structure can offer favorable microenvironment for immobilizing glucose oxidase and the direct electrochemistry process of glucose oxidase (GOD) at Ag@C modified glassy carbon electrode (GCE) was realized. The modified electrode exhibited good response to glucose. Under optimum experimental conditions the biosensor linearly responded to glucose concentration in the range of 0.05-2.5mM, with a detection limit of 0.02mM (S/N=3). The apparent Michaelis-Menten constant (KM(app)) of the biosensor is calculated to be 1.7mM, suggesting high enzymatic activity and affinity toward glucose. In addition, the GOD-Ag@C/Nafion/GCE shows good reproducibility and long-term stability. These results suggested that core-shell structured Ag@C is an ideal matrix for the immobilization of the redox enzymes and further the construction of the sensitive enzyme biosensor.

Amino-functionalized mesoporous silica modified glassy carbon electrode for ultra-trace copper(II) determination.

This paper described a facile and direct electrochemical method for the determination of ultra-trace Cu(2+) by employing amino-functionalized mesoporous silica (NH2-MCM-41) as enhanced sensing platform. NH2-MCM-41 was prepared by using a post-grafting process and characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM) and fourier transform infrared (FTIR) spectroscopy. NH2-MCM-41 modified glassy carbon (GC) electrode showed higher sensitivity for anodic stripping voltammetric (ASV) detection of Cu(2+) than that of MCM-41 modified one. The high sensitivity was attributed to synergistic effect between MCM-41 and amino-group, in which the high surface area and special mesoporous morphology of MCM-41 can cause strong physical absorption, and amino-groups are able to chelate copper ions. Some important parameters influencing the sensor response were optimized. Under optimum experimental conditions the sensor linearly responded to Cu(2+) concentration in the range from 5 to 1000 ng L(-1) with a detection limit of 0.9 ng L(-1) (S/N=3). Moreover, the sensor possessed good stability and electrode renewability. In the end, the proposed sensor was applied for determining Cu(2+) in real samples and the accuracy of the results were comparable to those obtained by inductively coupled plasma optical emission spectrometry (ICP-OES) method.

Enhanced photocatalytic properties of α-SnWO4 nanosheets modified by Ag nanoparticles

Decoration of silver nanoparticles (Ag-NPs) on surface of α-SnWO4 nanosheets has been achieved by a microwave-assisted deposition method. The as-synthesized products are structurally characterized by X-ray diffraction (XRD) and transmission electron microscopy (TEM). The results illustrate that Ag-NPs are evenly anchored onto α-SnWO4 surface to form close heterojunction and the amount of Ag nanoparticles grown on α-SnWO4 nanosheets can be well controlled by tuning Ag+ concentration. The photocatalytic properties of Ag-NPs/α-SnWO4 composites are evaluated by degrading methyl orange (MO) under visible-light irradiation. Ag-NPs/α-SnWO4 composites exhibit better photocatalytic properties than that of pure α-SnWO4, and Ag-NPs/α-SnWO4 (5mol% Ag) presents the best photocatalytic activity, whose photodegradation efficiency of MO is about 97% within 70min. In addition, the obtained samples demonstrate good recyclability. The enhanced photocatalytic properties was attributed to synergistic effect between Ag-NPs and α-SnWO4 nanosheets, which can increase absorption of visible light enabled by surface plasma resonance (SPR) of Ag-NPs and facilitate the separation of photogenerated electron-hole pairs.

Graphene-like carbon nitride nanosheet as a novel sensing platform for electrochemical determination of tryptophan

In this paper, a new and facile strategy has been demonstrated for the electrochemical determination of tryptophan (Trp), based on graphite-like carbon nitride (g-C3N4) nanosheets modified glassy carbon (CNNS/GC) electrode. The g-C3N4 nanosheets were obtained via exfoliating bulk graphitic carbon nitride (bg-C3N4), which was synthesized using a thermal poly-condensation process. The obtained g-C3N4 nanosheets were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), Fourier transform infrared (FTIR) spectroscopy and atomic force microscopy (AFM). The results confirmed graphite-like structure with thickness of about 6-8nm. The as-synthesized g-C3N4 nanosheets were closely attached to the surface of GC electrode to construct electrochemical sensor without needing any film-forming agents. The CNNS/GC electrode exhibited good electrocatalytic activity towards Trp, and hereby some parameters, including scan rate and pH effect on Trp determination were investigated. Under the optimum experimental conditions, the oxidation peak currents had good linear relationship with Trp concentrations in the range of 0.1-110μM and a detection limit of 0.024μM (S/N=3) was achieved. In addition, the obtained sensor showed good sensitivity, favorable repeatability, and long-term stability. Finally, the proposed electrochemical sensor has been successfully applied for the determination of Trp concentration in real samples with satisfactory results.