Zhonghua Xue

Highly dispersive Ag nanoparticles on functionalized graphene for an excellent electrochemical sensor of nitroaromatic compounds

A facile carbon radical reaction procedure and a chemical reduction method were proposed to synthesize Ag nanoparticles on functionalized graphene with uniform, high dispersion and excellent stability. The resultant material showed excellent electrocatalytic activity to nitroaromatic compounds and high sensitivity to the detection of nitroaromatic compounds.

Acetylsalicylic acid electrochemical sensor based on PATP–AuNPs modified molecularly imprinted polymer film

A novel electrochemical sensor based on molecularly imprinted polymer film has been developed for aspirin detection. The sensitive film was prepared by co-polymerization of p-aminothiophenol (p-ATP) and HAuCl(4) on the Au electrode surface. First, p-ATP was self-assembled on the Au electrode surface by the formation of Au-S bonds. Then, the acetylsalicylic acid (ASA) template was assembled onto the monolayer of p-ATP through the hydrogen-bonding interaction between amino group (p-ATP) and oxygen (ASA). Finally, a conductive hybrid membrane was fabricated at the surface of Au electrode by the co-polymerization in the mixing solution containing additional p-ATP, HAuCl(4) and ASA template. Meanwhile, the ASA was spontaneously imprinted into the poly-aminothiophenol gold nanoparticles (PATP-AuNPs) complex film. The amount of imprinted sites at the PATP-AuNPs film significantly increases due to the additional replenishment of ASA templates. With the significant increasing of imprinted sites and doped gold nanoparticles, the sensitivity of the molecular imprinted polymer (MIP) electrode gradually increased. The molecularly imprinted sensor was characterized by electrochemical impedance spectroscopy (EIS), differential pulse voltammetry (DPV), and cyclic voltammetry (CV). The linear relationships between current and logarithmic concentration were obtained in the range from 1 nmol L(-1) to 0.1 μmol L(-1) and 0.7 μmol L(-1) to 0.1 mmol L(-1). The detection limit of 0.3 nmol L(-1) was achieved. This molecularly imprinted sensor for the determination of ASA has high sensitivity, good selectivity and reproducibility, with the testing in some biological fluids also has good selectivity and recovery.

A amperometric biosensor for hydrogen peroxide by adsorption of horseradish peroxidase onto single-walled carbon nanotubes

Development of a highly sensitive nanostructured electrochemical biosensor based on the integrated assembly of horseradish peroxidase (HRP) and single-walled carbon nanotubes (SWNTs) is described. In this study, we describe the use of a sodium cholate suspension-dialysis method to adsorb the horseradish peroxidase (HRP) onto single-walled carbon nanotubes (SWNTs). We demonstrate that HRP-SWNTs conjugates can be assembled into amperometric biosensors which L-cysteine were assembled on a gold electrode through the covalent bond of S-Au and was used as a substrate for the immobilization of enzymes. Direct electron transfer of HRP is realized at SWNTs, and both anodic and cathodic currents of the redox reaction at the l-cysteine-HRP-SWNTs-modified gold film upon electrocatalysis are amplified. Meanwhile, experimental results reveal that HRP is stably immobilized onto the SWNTs and maintains inherent enzymatic activity toward H(2)O(2). The modified electrode shows high sensitivity toward H(2)O(2). A linear response to hydrogen peroxide measurement is obtained over the range from 1.0×10(-12) to 1.0×10(-11)M and an amperometric detection limit of 2.1×10(-13)M due to its bioelectrocatalytic reduction based on direct electron transfer between gold electrode and the active site of the HRP. The biosensor displays excellent operational, storage stability and highly sensitive. The excellent performance validates the integrated assembly as an attractive sensing element for the development of a new hydrogen peroxide amperometric biosensor.

Horseradish peroxidase supported on porous graphene as a novel sensing platform for detection of hydrogen peroxide in living cells sensitively

A viable and simple method for preparing porous graphene network using silver nanoparticles (AgNPs) etching was proposed, and a sensitive biosensor was constructed based on the porous graphene (PGN) and horseradish peroxidase (HRP) to measure the release of H2O2 from living cells. Owing to the large surface area and versatile porous structure, the use of nanoporous materials can significantly improve the analysis performance of the biosensor by loading large amounts of enzyme and accelerating diffusion rate. Meanwhile, the constructed electrode exhibited excellent electrochemical performance toward H2O2 with a determination limit as low as 0.0267nM and wide linear range of 7 orders of magnitude, which was superior to other H2O2 electrochemical sensors. Thus, this novel biosensor can detect the H2O2 release from living cells not only under normal physiological conditions (10-8-10-7M) but also in emergency state with the increased concentration (~10-4M). This work provides tremendous potential for real-time tracking of the secretion of H2O2 in different types of physiological and pathological investigations.

A simple and an efficient strategy to synthesize multi-component nanocomposites for biosensor applications.

We demonstrate that core-shell multi-component nanocomposites can be grown in situ at room temperature by a novel one-step approach without adding any reductant and stabilizer. We have presented a one-step method for the synthesis of multi-component nanocomposites in water solution, the multi-component nanocomposites could be produced directly and quickly in an in situ wet-chemical reaction. Here, Au-polypyrrole (PPy)/Prussian blue (PB) nanocomposites have been synthesized successfully under the same circumstance. With the addition of pyrrole monomers into mixture solutions, the autopolymerization of pyrrole into PPy and AuCl(4)(-) was reduced to elemental Au instantaneously as well as simultaneously. At the same time, PB produced along with elemental Au serving as a catalyst. Furthermore, we investigated the performance of Au-PPy/PB nanocomposites as amperometric sensor toward the reduction of H(2)O(2), which displayed high sensitivity, fast response and good stability. The peak current of H(2)O(2) increased linearly with the concentration of H(2)O(2) in the range from 2.5×10(-9) to 1.2×10(-6)M, and the low detection limit of 8.3×10(-10)M (S/N=3) was obtained. Therefore, this work provides a new pathway to design and fabricate novel multi-component nanocomposites, which have unique characteristics and hold great applications in the fields of sensors, electrocatalysis and others.

A novel electrochemical sensor for capsaicin based on mesoporous cellular foams

A novel electrochemical sensor for capsaicin using mesoporous cellular foams (MCFs) as the sensitive material is reported. The surface morphology and electrochemical properties of the prepared MCFs modified carbon paste electrode (CPE) were investigated by scanning electron microscopy (SEM), transmission electron microscopy (TEM), cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS). The proposed modified electrode shows high sensitivity towards the oxidation of capsaicin in 0.1 M perchloric acid solutions (pH 1.0). Under optimized conditions, the electrochemical oxidation current of capsaicin was found to be linearly related to the concentration over the range 0.76 to 11.65 μM with a correlation coefficient of 0.9990, and the detection limit was found to be 0.08 μM at a signal-to-noise ratio of 3. The proposed electrochemical sensor was successfully applied to the determination of capsaicin by using standard addition method with satisfactory results.

Quenching of the electrochemiluminescence of Ru(bpy)32+/TPA by malachite green and crystal violet

Efficient and stable quenching of electrochemiluminescence of Ru(bpy)3(2+)/TPA by malachite green(MG) and crystal violet(CV) at the glass carbon (GC) electrode is reported. A novel quenching mechanism has been proposed. Resonance energy transfer from the excited-state luminophore Ru(bpy)3(2+*) to MG/CV and dynamic quenching are suggested as the mechanism for quenching ECL. The quenching mechanism is discussed in detail based on UV-visible absorption spectra, cyclic voltammograms, ECL curves and fluorescence methods. MG shows more efficient quenching than CV. Moreover, the quenched ECL intensity versus the concentration of MG and CV are linear over the concentration ranges of 8 × 10(-10)-8 × 10(-7)M and 3.46 × 10(-9)-5.5 × 10(-7)M, respectively. The corresponding limit of detection (LOD) was 1.0 × 10(-10)M for MG and 1.1 × 10(-10)M for CV (S/N=3).

Mini Review: Electroanalytical Sensors of Mesoporous Silica Materials

Mesoporous silica materials are promising substrates for electroanalytical sensors and electrocatalysis. Their characteristics include uniform pore sizes, surface areas in excess of 1000 m2 g−1, and long-range ordering of the packing of pores. The size scale, aspect ratio, and properties of mesoporous silica provide advantages in a variety of sensor applications. To improve performance, miniaturize platforms, and expand applications for trace analysis, novel materials with high sensitivity and rapid response have been developed and employed in recent years. These materials include pure mesoporous silica, mesoporous silica functionalized with organic groups, and composite or hybrid mesoporous silica. In this review, recent advances are outlined involving the application of mesoporous silica-based materials in electroanalytical sensors.

An electrochemical glutathione biosensor: Ubiquinone as a transducer

In this paper, coenzyme Q10 (Ubiquinone, CoQ10) was used for the first time as a transducer to construct electrochemical biosensor for effectively detecting γ-L-glutamyl-L-cysteinyl-glycine (glutathione, GSH). CoQ10 modified electrode was fabricated by attaching its gel mixed with multi-walled carbon nanotubes (MWNTs)/ionic liquid (IL). In the optimum conditions, based on the increasing of reduction peak current of CoQ10 caused by GSH through voltammetric technology, it was found that the peak current of CoQ10 was linear with the concentration of GSH in the range from 4.0×10(-9) to 2.0×10(-7)mol L(-1) at the pH 7.00, and the limit of detection was 3.2×10(-10)mol L(-1) (S/N=3). The results revealed that this method could be used to determine GSH in actual blood samples with the superiority of excellent selectivity, high stability and sensitivity. The strategy explored here might provide a new pathway to design novel multi-function transducers for detecting GSH, which has unique characteristic and potential application in the fields of sensor and medical diagnosis.

Heterogeneous Consecutive Electron Transfer at Graphite Electrodes under Steady State

In this report, the theory based on thin-layer cyclic voltammetry (TLCV) for consecutive electron transfer (ET) across the interface between two immiscible electrolyte solutions (ITIES) is well developed and experimentally verified. The voltammetric responses to multistep electron transfer at the ITIES are predicted by numerical simulations. Moreover, the impact of empirical parameters on the shape of the multistep current-voltage curve has been examined. The results obtained not only give information regarding the effect of the concentration ratio of the reactants in two phases and the thin-layer thickness on multistep electron transfer, but also prove the excellent agreement between simulations and experiments. The model system of two-step electron transfer of ZnTPP/[Fe(CN)₆]⁴⁻ was studied, indicating that the Bulter-Volmer (B-V) theory is suitable for the consecutive electron transfer. Thus, TLCV is demonstrated to be a useful means for investigating the kinetics of heterogeneous consecutive ET.