Cunlan Guo

Novel nonenzymatic hydrogen peroxide sensor based on iron oxide-silver hybrid submicrospheres.

Fe(3)O(4)-Ag hybrid submicrosphere was synthesized and developed as hydrogen peroxide sensor in this study. The hybrid sphere was fabricated via a two-step route, and proved by characterizations such as TEM, SEM, EDX, and XPS. Recent studies of hydrogen peroxide sensor based on silver nanoparticles inspired us to study the electrocatalytic property of the as-prepared submicrosphere. Though the Ag amount is quite little in the hybrid spheres, the electrochemical sensor constructed by the hybrid spheres exhibited fast, stable and well-defined electrocatalytic activity towards H(2)O(2) reduction, which should be the contribution of the combination of Fe(3)O(4) and Ag. The detection limit of H(2)O(2) was also found to be 1.2microM, which was lower than some enzyme-based biosensors.

Carbon nanotube/raspberry hollow Pd nanosphere hybrids for methanol, ethanol, and formic acid electro-oxidation in alkaline media

In this paper, raspberry hollow Pd nanospheres (HPNs)-decorated carbon nanotube (CNT) was developed for electro-oxidation of methanol, ethanol, and formic acid in alkaline media. The electrocatalyst was fabricated simply by attaching HPNs onto the surface of CNT which had been functionalized by polymer wrapping. The as-prepared HPN-CNTs (CHPNs) were characterized by transmission electron microscopy (TEM), scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDX), and X-ray photoelectron spectroscopy (XPS). The increasing interest and intensive research on fuel cell inspire us to investigate the electrocatalytic properties of the prepared nanostructures. Besides that, previous reports about alkaline other than acidic media could supply a more active environment guide us to examine the electrocatalytic properties in alkaline electrolyte. It is found that this novel hybrid electrocatalyst exhibits excellent electrocatalytic properties and can be further applied in fuel cells, catalysts, and sensors.

Facile synthesis of urchin-like gold submicrostructures for nonenzymatic glucose sensing

Urchin-like gold submicrostructures (UGS) were successfully synthesized by a seed-mediated method which is quite facile and does not need any template or surfactant agent. The effect of the added silver seeds on the morphology and size of final products were investigated, and a possible growth mechanism of crystals was proposed. Electrochemical characterization indicated that these UGS have better catalytic activity for the glucose oxidation compared with flower-like gold submicrostructures (FGS), which could be ascribed to its higher surface to volume ratio. An electrochemical nonenzymatic glucose sensor was fabricated simply by casting the UGS and Nafion solution onto glass carbon electrode. This sensor displays a wide linear range from 0.2 to 13.2mM with a high sensitivity of 16.8 μA mM(-1)cm(-2), and a detection limit of 10 μM. The unique properties of this sensor, such as fast response and well stability reveal the potential application of the UGS based materials in nonenzymatic detection of glucose.

Interaction between DNA and microcystin-LR studied by spectra analysis and atomic force microscopy.

Microcystin-LR (MC-LR) is one of the hepatotoxins produced by cyanobacteria in the eutrophicated fresh water. In this work, the minor groove binding mode of MC-LR to plasmid DNA was explored by using UV and fluorescence spectra, and the binding characteristics of MC-LR for plasmid DNA were calculated via the fluorescence quenching of ethidium bromide (EB) and mole ratio method. Furthermore, atomic force microscopy (AFM) was used to observe DNA morphology change in the presence of MC-LR. With the increasing concentration of MC-LR, circle DNA strands twined gradually to rod condensates. The possible reason for the condensation might be the masking of the electrostatic repulsion between DNA double strands by MC-LR. The present study might provide useful information for the pathopoiesis mechanism of MC-LR. More, because the condensation of DNA could affect the progresses of gene expression and protein transcription, it may implicate another trend to explore the nosogenesis of MC-LR.

Seed-Mediated Synthesis of Au Nanocages and Their Electrocatalytic Activity towards Glucose Oxidation

We report a modified seed-mediated approach for the synthesis of uniform Au nanocages (AuNCs). HAuCl(4) was reduced in an aqueous mixture of hexamethylenetetramine (HMT), poly(N-vinyl-2-pyrrolidone) (PVP), and AgNO(3). The nanocages were (54.6+/-13.3) nm in outer-edge length and about 12 nm in wall thickness. The structure of the AuNCs was characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray energy dispersive spectroscopy (EDS), X-ray diffraction (XRD), Fourier-transform infrared (FTIR) spectroscopy, and X-ray photoelectron spectroscopy (XPS). Morphological changes associated with the seed-mediated growth of Au nanoparticles (AuNPs) in the absence of HMT or PVP were examined. The results demonstrate that both PVP and HMT play important roles in the formation of the nanocage structure. The function of AgNO(3) was also studied. A possible formation mechanism for the AuNCs was investigated by monitoring TEM images of the Au nanostructures formed at various reaction times. The electrocatalytic activity of the AuNCs towards the oxidation of glucose was explored, and a nonenzymatic glucose sensor with high sensitivity and good stability was further fabricated. To the best of our knowledge, this is the first report of the preparation of AuNCs by a seed-mediated strategy and of the application of AuNCs in the electrocatalytic oxidation of glucose. Our results should facilitate the creation of novel nanomaterials with various morphologies and the exploration of their applications in nanotechnological, optical, catalytic, and materials science fields.

Fabrication, characterization, and application in surface-enhanced Raman spectrum of assembled type-I collagen-silver nanoparticle multilayered films.

In this paper, we report a facile method for the fabrication of type-I collagen-silver nanoparticles (Ag NPs) multilayered films by utilizing type-I collagen as a medium. These samples were characterized by UV-vis spectra photometer, atomic force microscopy, scanning electron microscopy, and Fourier transform IR spectrum. Experimental results show that collagen molecules serve as effective templates to assemble Ag NPs into multilayer films. These samples exhibit high surface-enhanced Raman scattering (SERS) enhancement abilities. For example, EF(nu(cc)) (EF means enhancement factor) at 1592 cm(-1) in the SERS spectrum of 4-aminothiophenol on seven-layered substrates was calculated to be 1.81 x 10(5), which is larger than that reported in several literatures. The EFs increased as the layer number of multilayer films increases.

Atomic force microscopy and surface-enhanced Raman scattering detection of DNA based on DNA-nanoparticle complexes

We report a simple method for the label-free detection of double-stranded DNA using surface-enhanced Raman scattering (SERS). We prepared cetyltrimethylammonium bromide (CTAB)-capped silver nanoparticles and a DNA-nanoparticle complex by adding silver nanoparticles to lambda-DNA solutions. In the present study, the utilization of CTAB-capped silver nanoparticles facilitates the electrostatic interaction between DNA molecules and silver nanoparticles; at the same time, the introduction of DNA avoids adding aggregating agent for the formation of nanoparticle aggregates to obtain large enhancement of DNA, because the DNA acts as both the probe molecules and aggregating agent of Ag nanoparticles. Atomic force microscopy (AFM) studies show that the morphology of DNA-Ag nanoparticle complexes seems to be determined by the concentrations of the DNA and the nanoparticles. Surface-enhanced Raman scattering (SERS) studies show that the morphology of the complexes plays a significant role in the intensity of SERS signals of DNA, and the best signal enhancement of DNA can be obtained by fine-tuning the experimental parameters. The SERS spectrum affords important structural information about the bases, phosphate backbone, and the conformation of DNA after mixing the DNA solutions with the Ag sol.

Type I collagen-mediated synthesis of noble metallic nanoparticles networks and the applications in Surface-Enhanced Raman Scattering and electrochemistry

In this paper, we demonstrated an effective environmentally friendly synthesis route to prepare noble metallic (Au, Ag, Pt and Pd) nanoparticles (NPs) networks mediated by type I collagen in the absence of any seeds or surfactants. In the reactions, type I collagen served as stabilizing agent and assembly template for the synthesized metallic NPs. The hydrophobic interaction between collagen and mica interface as well as the hydrogen bonds between inter- and intra-collagen molecules play important roles in the formation of collagen-metallic NPs networks. The noble metallic NPs networks have many advantages in the applications of Surface-Enhanced Raman Scattering (SERS) and electrochemistry detection. Typically, the as-prepared Ag NPs networks reveal great Raman enhancement activity for 4-ATP, and can even be used to detect low concentration of DNA base, adenine, without any label step. Furthermore, the cyclic voltammograms showed Pt NPs networks have good electrocatalytic ability for the reduction of O(2).

Surface-Relevant Regulable DNA Toroids Induced by Dopamine

Dopamine (2-(3,4-dihydroxyphenyl)ethylamine) is known as a natural chemical neurotransmitter and is also a cytotoxic and genotoxic molecule for cell apoptosis. In this work, the interaction of DNA with dopamine was investigated. Though the electrostatic interaction of DNA and dopamine was weak in aqueous solution, dopamine condensed circular pBR322 DNA into toroids on the mica surface cooperatively with ethanol. The formed DNA toroids came from the shrinking of DNA that was driven by ethanol-enhanced DNA-dopamine electrostatic interaction. The size of the DNA toroids could be modulated by varying the concentration of dopamine. This study offers useful information about the DNA condensation induced by monovalent cations and the sample preparation for AFM measurement and application. On the other hand, this work provides the potential strategies to prepare morphology and size controllable DNA condensates, which have valuable applications in gene transfection and nanotechnology.

Atomic Force Microscopic Study of Low Temperature Induced Disassembly of RecA−dsDNA Filaments

The assembly and disassembly of RecA-DNA nucleoprotein filaments on double-stranded DNA (dsDNA) or single-stranded DNA (ssDNA) are important steps for homologous recombination and DNA repair. The assembly and disassembly of the nucleoprotein filaments are sensitive to the reaction conditions. In this work, we investigated different morphologies of the formed nucleoprotein filaments at low temperature under different solution conditions by atomic force microscopy (AFM). We found that low temperature and long keeping time could induce the incomplete disassembly of the formed nucleoprotein filaments. In addition, when the formed filaments were kept at -20 degrees C for 20 h with 1,4-dithiothreitol (DTT), the integrated filaments disassembled. It was similar to the case under the same condition without anything added. However, when glycerol was used as a substitute for DTT, there was no obvious disassembly at the same condition. Oppositely, when the formed filaments were kept at 4 degrees C for 20 h, the disassembly with additional DTT was not as obvious as the case at -20 degrees C for 20 h, whereas the case with additional glycerol disassembled. The experiments indicated the effect of cold denaturation on the interaction of DNA and RecA. Meanwhile, the study of these phenomena can supply guidelines for the property and stability of RecA as well as the relevant roles of influencing factors to RecA and DNA in further theoretical studies.