Zhenxin Wang

Nonenzymatic amperometric determination of glucose by CuO nanocubes-graphene nanocomposite modified electrode

Here, we report a nonenzymatic amperometric glucose sensor based on copper oxide (CuO) nanocubes-graphene nanocomposite modified glassy carbon electrode (CuO-G-GCE). In this case, the graphene sheets were cast on the GCE directly. CuO nanocubes were obtained by oxidizing electrochemically deposited Cu on the graphene. The morphology of CuO-G nanocomposite was characterized by scanning electron microscopy. The CuO-G-GCE-based sensor exhibited excellent electrocatalytic activity and high stability for glucose oxidation. Under optimized conditions, the linearity between the current response and the glucose concentration was obtained in the range of 2μM to 4mM with a detection limit of 0.7μM (S/N=3), and a high sensitivity of 1360μAmM(-1)cm(-2). The proposed electrode showed a fast response time (less than 5s) and a good reproducibility. The as-made sensor was applied to determine the glucose levels in clinic human serum samples with satisfactory results. In addition, the effects of common interfering species, including ascorbic acid, uric acid, dopamine and other carbohydrates, on the amperometric response of the sensor were investigated and discussed in detail.

Fluorescence resonance energy transfer quenching at the surface of graphene quantum dots for ultrasensitive detection of TNT

This paper for the first time reports a chemical method to prepare graphene quantum dots (GQDs) from GO. Water soluble and surface unmodified GQDs, serving as a novel, effective and simple fluorescent sensing platform for ultrasensitive detection of 2,4,6-trinitrotoluene (TNT) in solution by fluorescence resonance energy transfer (FRET) quenching. The fluorescent GQDs can specifically bind TNT species by the π-π stacking interaction between GQDs and aromatic rings. The resultant TNT bound at the GQDs surface can strongly suppress the fluorescence emission by the FRET from GQDs donor to the irradiative TNT acceptor through intermolecular polar-polar interactions at spatial proximity. The unmodified GQDs can sensitively detect down to ~0.495 ppm (2.2 μM) TNT with the use of only 1 mL of GQDs solution. The simple FRET-based GQDs reported here exhibit high and stable fluorescence. Eliminating further treatment or modification, this method simplifies and shortens the experimental process. It possesses good assembly flexibility and can thus find many applications in the detection of ultratrace analytes.

Layer-by-layer assembly of multilayer films composed of avidin and biotin-labeled antibody for immunosensing

Protein multilayers composed of avidin and biotin-labeled antibody (bio-Ab) were prepared on gold surface by layer-by-layer assembly technology using the high specific binding constant (K(a): approximately 10(15) M(-1)) between avidin and biotin. The assembly process of the multilayer films was monitored by using real-time BIA technique based on surface plasmon resonance (SPR). The multilayer films were also characterized by electrochemical impedance spectroscopy (EIS) and reflection absorption Fourier transform infrared spectroscopy (FTIR). The results indicate that the growth of the multilayer is uniform. From response of SPR for each layer, the stoichiometry S for the interaction between avidin and bio-Ab is calculated to be 0.37 in the multilayer whereas 0.82 in the first layer. The protein mass concentration for each layer was also obtained. The schematic figure for the multilayer assembly was proposed according to the layer mass concentration and S value. The utility of the mutilayer films for immunosensing has been investigated via their subsequent interaction with hIgG. The binding ability of the multilayer increased for one to three layers of antibody, and then reach saturation after the fourth layer. These layer-by-layer constructed antibody multilayers enhance the binding ability than covalently immobilized monolayer antibody. This technology can be also used for construction of other thin films for immunosensing and biosensor.

DNA electrochemical biosensor based on thionine-graphene nanocomposite

A novel protocol for development of DNA electrochemical biosensor based on thionine-graphene nanocomposite modified gold electrode was presented. The thionine-graphene nanocomposite layer with highly conductive property was characterized by scanning electron microscopy, transmission electron microscopy, cyclic voltammetry and electrochemical impedance spectroscopy. An amino-substituted oligonucleotide probe was covalently grafted onto the surface of the thionine-graphene nanocomposite by the cross-linker glutaraldehyde. The hybridization reaction on the modified electrode was monitored by differential pulse voltammetry analysis using an electroactive intercalator daunomycin as the indicator. Under optimum conditions, the proposed biosensor exhibited high sensitivity and low detection limit for detecting complementary oligonucleotide. The complementary oligonucleotide could be quantified in a wide range of 1.0 × 10(-12) to 1.0 × 10(-7)M with a good linearity (R(2)=0.9976) and a low detection limit of 1.26 × 10(-13)M (S/N=3). In addition, the biosensor was highly selective to discriminate one-base or two-base mismatched sequences.

Functional gold nanoparticle-peptide complexes as cell-targeting agents.

In this paper, we report a novel approach using peptide CALNN and its derivative CALNNGGRRRRRRRR (CALNNR(8)) to functionalize gold nanoparticles for intracellular component targeting. The translocation is effected by the nanoparticle diameter and CALNNR(8) surface coverage. The intracellular distributions of the complexes are change from the cellular nucleus to the endoplasmic reticulum by increasing the density of CALNNR(8) at a constant nanoparticle diameter. Additionally, increasing the nanoparticle diameter at a constant density of CALNNR(8) leads to less cellular internalization. These translocations of the complexes cause unique colorimetric expressions of the cell structure. The cell viability is affected by the internalized gold nanoparticle-peptide complexes in terms of quantities of particles per cell. In addition, the intracellular distribution of the fluorescence quenching is investigated by a fluorescent confocal scanning laser microscopy, which also gives further evidence of intracellular distribution of the gold nanoparticle-peptide complexes.

Conjugation of NaGdF4 upconverting nanoparticles on silica nanospheres as contrast agents for multi-modality imaging

Here, we report the covalently conjugation of lanthanide doped NaGdF4:Yb(3+), Er(3+)@NaGdF4 upconverting nanoparticles (UCNPs) on methylphosphonate functionalized silica nanospheres (pSi NPs) for in vivo upconversion luminescence (UCL), T1-weighted magnetic resonance (MR), and X-ray computed tomography (CT) multi-modality imaging. The nanocomposites (pSi@UCNPs) were synthesized by a facile ligand exchange strategy. The hydrophobic pSi@UCNPs were transferred into aqueous solution by surface coating Pluronic F127. The Pluronic F127 coated pSi@UCNPs (pSi@UCNPs@F127) exhibit excellent stability in biological medium, inappreciable cytotoxicity and negligible organ toxicity. The pSi@UCNPs@F127 also shows brighter UCL, and higher CT/MR enhancements than that of Pluronic F127 coated NaGdF4:Yb(3+), Er(3+)@NaGdF4 UCNP. In detail, the capability of pSi@UCNPs@F127 as high performance contrast agents for in vivo multi-modality (UCL/MR/CT) imaging is evaluated successfully through small-animal experiments.

Electrochemical synthesis of polyaniline nanoparticles

Polyaniline nanoparticles were prepared on a highly oriented pyrolytic graphite (HOPG) surface from dilute polyaniline acidic solution (1 mM aniline + 1 M HClO4) using a pulsed potentiostatic method. Electrochemistry, Fourier transform infrared external reflection spectroscopy (FT-IR-ERS), X-ray photoelectron spectroscopy (XPS) and tapping-mode atomic force microscopy (TMAFM) were: used to characterize the composition and structure of the polyaniline nanoparticles. FT-IR-ERS and XPS results revealed that the polyaniline was in its emeraldine form. TMAFM measurement showed that the electropolymerized polyaniline nanoparticles dispersed on the:HOPG surface with a coverage of about 10(10) cm(-2). These nanoparticles were disk-shaped having a height of 10(-30) Angstrom and an apparent diameter varying from 200 to 600 Angstrom. The particle dimensions increased with the electropolymerization charge (Q) over the interval from 5.7 to 19.3 mu C cm(-2) (C) 2000 Elsevier Science S.A. All rights reserved.

Functionalized inorganic-organic composite material derivated by sol-gel for construction of mediated amperometric hydrogen peroxide biosensor

A novel functionalized inorganic-organic hybrid material with cation exchange property was prepared by sol-gel method. The H2O2 biosensor was fabricated by simply dipping the horseradish peroxidase-containing functionalized membrane modified electrode into Meldolas blue (MDB) solution. MDB was adsorbed and firmly immobilized within the membrane. The electrochemical behavior of MDB incorporated in the membrane was more reversible compared with that of the solution species and suitable as mediator for the horseradish peroxidase. The response time was less than 25 s. Linear range is up to 0.6 mM (COH. coeff. 0.9998) with detection Limit of 9 x 10(-7) M. High sensitivity of 75 nA mu M cm(-2) was obtained due to high MDB-loading. The biosensor exhibited a good stability

Microarray-Based Study of Carbohydrate-Protein Binding by Gold Nanoparticle Probes

In order to develop a novel high-throughput tool for monitoring carbohydrate-protein interactions, we prepared carbohydrate or glycoprotein microarrays by immobilizing amino modified carbohydrates on aldehyde-derivatized glass slides or glycoprotein on epoxide-derivatized glass slides and carried out lectin binding experiments by using these microarrays, respectively. The interaction events are marked by attachment of gold nanoparticles followed by silver deposition for signal enhancement. The attachment of the gold nanoparticles is achieved by standard avidin-biotin chemistry. The detection principle is resonance light scattering (RLS). The well-defined recognition systems, namely, three monosaccharides (Man-alpha, Glc-beta and Gal-beta) or three glycoproteins (Asf, RNase A and RNase B) with two lectins (ConA and RCA120), were chosen here to establish the RLS assay, respectively. Highly selective recognition of carbohydrate-protein down to 25.6 pg/mL for RCA120 in solution and 8 microM for Gal-beta and 32 ng/mL for Asf on the microarray spots is demonstrated.

A generic approach to monofunctionalized protein-like gold nanoparticles based on immobilized metal ion affinity chromatography

Due to their chemical, optical and electronic properties, metal nanoparticles (NPs) are essential components of new biosensors and self-assembled nanodevices. The ability to vary and control the surface composition of NPs with molecular accuracy is crucial for many envisioned applications and has been a major focus of research. The average composition can be varied through synthesis or ligand exchange by using different capping-ligand mixtures. Pioneering work by Alivisatos’ group led to the separation of NPs with a defined number of DNA strands by gel electrophoresis. The drawback of gel electrophoresis is that it is not easily scalable and is limited to DNA. Monofunctionalization based on solid-phase coupling and solid-phase ligand-exchange reactions has recently been reported for small amphiphilic NPs. We have recently developed a route to protein-like metal NPs based on self-assembled monolayers of peptides. The protein-like behaviour of NPs enables a wide range of biochemistry techniques to be applied. Separation of proteins has been a major challenge in the past decades, and powerful tools have been created to achieve this task. In this communication, we report the power of immobilized metal ion affinity chromatography (IMAC), a method developed and optimized for the purification of recombinant proteins, to separate peptide-capped NPs with a given number of molecular labels. This simple, scalable and analytical strategy is applicable to the preparation of NPs bearing a predefined number of virtually any water-soluble chemical moieties. Peptide-capped NPs were prepared by mixing 6 nm gold NPs with peptide solutions. The excess peptide was removed by size-exclusion chromatography. The peptide solutions comprised different proportions of the peptide CALNN (“matrix” peptide) and of an extended peptide, namely CALNNGHHHHHHGKbiotinG (“functional” peptide). The extension of the functional peptide is composed of two independent entities: the His-tag (a sequence of 6 histidines), which is used for its ability to bind to immobilized chelated transition metal ions such as nickel, followed by a label (Figure 1). Because