Liang-Hong Guo

Synthesis and characterization of multi-functional nanoparticles possessing magnetic, up-conversion fluorescence and bio-affinity properties

Multi-functional nanoparticles possessing magnetic, up-conversion fluorescence and bio-affinity properties were synthesized and characterized. The particles have a core/shell structure. Iron oxide nanoparticles of 5–15 nm diameter were synthesized as the magnetic core. The core was covered with ytterbium and erbium co-doped sodium yttrium fluoride (NaYF4:Yb,Er), an efficient infrared-to-visible up-conversion phosphor. The phosphor shell was prepared by co-precipitation of the rare-earth metal salts with fluoride in the presence of EDTA and the magnetic nanoparticle. After the magnetic/fluorescent hybrid particle was coated with SiO2 and activated with glutaraldehyde, streptavidin was immobilized on the particle. The magnetic/fluorescent nanoparticles were found by transmission electron microscopy to be well-dispersed spherical particles with an average diameter of 68 nm. Both energy dispersive X-ray microanalysis and X-ray fluorescence spectra revealed the existence of iron in the particle. Measurements performed on a vibrating sample magnetometer obtained a strong magnetic response for the particle and fluorescence measurements demonstrated its up-conversion property. X-Ray diffraction analysis suggests the phosphor shell has the same structure as the pure NaYF4:Yb,Er nanoparticles we prepared in a previous study (G. S. Yi, H. C. Lu, S. Y. Zhao, Y. Ge, W. J. Yang, L. H. Guo, D. P. Chen and J. Cheng, submitted). Streptavidin-coated magnetic/fluorescent particles were found to bind specifically to a glass slide spotted with biotinylated IgG and emit up-conversion fluorescence, confirming the successful coating of the protein and retention of its optical activity and bio-affinity.

Direct electrochemistry of proteins and enzymes

Publisher Summary This chapter discusses direct electrochemistry of metalloproteins and redox enzymes. The electron transport chain is composed of a number of electron transfer complexes firmly bound to the biological membrane, and electron-carrying groups in these complexes are flavins, iron–sulfur clusters, heme groups, and copper ions. Therefore, electron transfer reactions within and between proteins play an important role in biological energy transduction, and, not surprisingly, there is a continuing interest in the studies of electron transfer processes in biology. More recently, direct electron transfer between redox enzymes and electrodes has been achieved because of more careful control of electrode surfaces. The need for biocompatible surfaces in bioelectrochemistry has stimulated the development of electrode surface engineering techniques, and protein electrochemistry has been reported at conducting polymer electrodes and in membranes. The combination of direct protein electrochemistry with spectroscopic methods may offer a novel way of investigating structure-function relationships in electron transport proteins.

Two-Dimensional Interface Engineering of a Titania−Graphene Nanosheet Composite for Improved Photocatalytic Activity

A graphene-based two-dimensional (2D) nanoplatform provides new opportunities for fabricating 2D heterojunction interfaces to fortify charge transfer in semiconductor assemblies. In this report, TiO2 nanosheet/graphene composite based 2D-2D heterojunctions were fabricated by a solvothermal process. Microscopic and spectroscopic characterization revealed a homogeneous sheetlike morphology with intimate interfacial contact between the TiO2 nanosheet and graphene due to chemical interactions. Compared with 0D-2D Degussa P25 (TiO2)/graphene and 1D-2D TiO2 nanotube/graphene composites, the 2D-2D TiO2 nanosheet/graphene hybrid demonstrated higher photocatalytic activity toward the degradation of rhodamine B and 2,4-dichlorophenol under UV irradiation. Radical trapping and ESR experiments revealed the enhanced generation of ·OH and O2(•-) in the 2D-2D heterojunction system. By analyzing TiO2 excited state deactivation lifetime, the interfacial electron transfer rates determined for 0D-2D, 1D-2D, and 2D-2D TiO2/graphene composites were 1.15 × 10(8) s(-1), 3.47 × 10(8) s(-1), and 1.06 × 10(9) s(-1), respectively. It was therefore proposed that the fast charge separation in the TiO2 nanosheet/graphene photocatalyst promoted the generation of reactive oxygen species and enhanced the photodegradation reactions. The results underscore the key role of nanomaterial dimensionality in interfacial charge transfer processes.

Single-walled carbon nanotubes and graphene oxides induce autophagosome accumulation and lysosome impairment in primarily cultured murine peritoneal macrophages.

The wide application of carbon nanomaterials in various fields urges in-depth understanding of the toxic effects and underlying mechanisms of these materials on biological systems. Cell autophagy was recently recognized as an important lysosome-based pathway of cell death, and autophagosome accumulation has been found to be associated with the exposure of various nanoparticles, but the underlying mechanisms are still uncertain due to the fact that autophagosome accumulation can result from autophagy induction and/or autophagy blockade. In this study, we first evaluated the toxicity of acid-functionalized single-walled carbon nanotubes and graphene oxides, and found that both carbon nanomaterials induced adverse effects in murine peritoneal macrophages, and GOs were more potent than AF-SWCNTs. Both carbon nanomaterials induced autophagosome accumulation and the conversion of LC3-I to LC3-II. However, degradation of the autophagic substrate p62 protein was also inhibited by both nanomaterials. Further analyses on lysosomes revealed that both carbon nanomaterials accumulated in macrophage lysosomes, leading to lysosome membrane destabilization, which indicates reduced autophagic degradation. The effects of AF-SWCNTs and GOs on cell autophagy revealed by this study may shed light on the potential toxic mechanism and suggest caution on their utilization.

Structure-based investigation on the binding interaction of hydroxylated polybrominated diphenyl ethers with thyroxine transport proteins

Polybrominated diphenyl ethers (PBDEs) have been shown to alter thyroid hormone level in experimental animals. One of the possible mechanisms for hormone disruption is the competitive binding of hydroxylated PBDEs (OH-PBDEs) with hormone transport proteins. In this study, binding interaction of 14 diversely structured OH-PBDEs with two thyroxine transport proteins was investigated by fluorescence displacement assay, circular dichroism, and molecular docking. Binding affinity of the 14 OH-PBDEs with transthyretin (TTR) and thyroxine-binding globulin (TBG) was measured by competitive fluorescence displacement assay. The binding constant was found to fall in the range of 1.4 x 10⁷ M and 6.9 x 10⁸ M⁻¹ for TTR, and between 6.5 x 10⁶ M⁻¹ and 2.2 x 10⁸ M⁻¹ for TBG. Binding affinity increased significantly with bromination number from 1 to 4, whereas 5- and 6-brominated diphenyl ethers did not show any further increase. Protein secondary structural change of TTR and TBG upon binding with 5-OH-BDE-047 was investigated by circular dichroism. The spectral change displayed a pattern similar to the one with thyroxine, suggesting that the environmental chemical binds to the two proteins at the same sites as the hormone. In molecular docking analysis, a ligand-binding channel in TTR was revealed for OH-PBDEs binding, which appeared to be mostly hydrophobic inside but guarded by positively charged residue Lys15 at the entrance. Binding affinity of the 14 OH-PBDEs with TTR could be rationalized reasonably well by their pocket binding mode and hydrophobic characteristics. Based on the binding constant obtained in this work, possibility of in vitro competitive displacement of thyroid hormones from the transport proteins by OH-PBDEs was evaluated.

Switching Oxygen Reduction Pathway by Exfoliating Graphitic Carbon Nitride for Enhanced Photocatalytic Phenol Degradation

The selectivity of molecular oxygen activation on the exfoliated graphitic carbon nitride (g-C3N4) and its influence on the photocatalytic phenol degradation process were demonstrated. Compared with bulk g-C3N4, the exfoliated nanosheet yielded a 3-fold enhancement in photocatalytic phenol degradation. ROS trapping experiments demonstrated that although the direct hole oxidation was mainly responsible for phenol photodegradation on both g-C3N4 catalysts, molecular oxygen activation processes on their surface greatly influenced the whole phenol degradation efficiency. Reactive oxygen species and Raman spectroscopy measurements revealed that oxygen was preferentially reduced to ·O2(-) by one-electron transfer on bulk g-C3N4, while on g-C3N4 nanosheet the production of H2O2 via a two-electron transfer process was favored due to the rapid formation of surface-stabilized 1,4-endoperoxide. The latter process not only promotes the separation of photogenerated electron-hole pairs but also greatly facilitates reactive oxygen species formation and subsequently enhances phenol degradation.

Light-Induced Efficient Molecular Oxygen Activation on a Cu(II)- Grafted TiO2/Graphene Photocatalyst for Phenol Degradation

An efficient photocatalytic process involves two closely related steps: charge separation and the subsequent surface redox reaction. Herein, a ternary hybrid photocatalytic system was designed and fabricated by anchoring Cu(II) clusters onto a TiO2/reduced graphene oxide (RGO) composite. Microscopic and spectroscopic characterization revealed that both TiO2 nanoparticles and Cu(II) clusters were highly dispersed on a graphene sheet with intimate interfacial contact. Compared with pristine TiO2, the TiO2/RGO/Cu(II) composite yielded an almost 3-fold enhancement in the photodegradation rate toward phenol degradation under UV irradiation. Electron spin resonance (ESR) spectra and electrochemical measurements demonstrated that the improved photocatalytic activity of this ternary system benefitted from the synergetic effect between RGO and Cu(II), which facilitates the interfacial charge transfer and simultaneously achieves in situ generation of H2O2 via two-electron reduction of O2. These results highlight the importance to harmonize the charge separation and surface reaction process in achieving high photocatalytic efficiency for practical application.

Photoelectrochemical detection of oxidative DNA damage induced by Fenton reaction with low concentration and DNA-associated Fe2+.

The metal ion dependent decomposition of hydrogen peroxide, the so-called Fenton Reaction, yields hydroxyl radicals that can cause oxidative DNA damage both in vitro and in vivo. We have previously reported a photoelectrochemical sensor for the detection of oxidative DNA damage induced by an Fe(2+)-mediated Fenton Reaction, using a DNA intercalator as a photoelectrochemical signal reporter (Liang, M.; Guo, L.-H. Environ. Sci. Technol. 2007, 41, 658). The intercalator binds less to the damaged DNA in the sensor film than the native form, resulting in a reduction in the measured photocurrent. In this report, some mechanistic aspects of the sensor were investigated. It was found that Fe(2+) alone (without the coexistence of H(2)O(2)) suppressed the photocurrent of the intercalator bound to the DNA film in a pH-dependent manner. Similar pH dependence was observed for the zeta potential of the tin oxide nanoparticle colloid used in the preparation of the semiconductor electrode, leading to the hypothesis that the metal ion binds to the surface oxide groups on the electrode and quenches the photoelectrochemical response. At pH 3, the quenching effect was reduced substantially to permit the detection of DNA damage by as low as 10 muM Fe(2+) and 40 microM H(2)O(2), a concentration that is within the physiologically relevant range. It was also found that Fe2+ ions associated with the DNA in the sensor film and participated in the DNA damage reaction, a mechanism that has been implicated in previous studies on metal carcinogenesis.

Molecular toxicology of polybrominated diphenyl ethers: nuclear hormone receptor mediated pathways

Polybrominated diphenyl ethers (PBDEs) are used in large quantities as flame retardant additives in commercial products. Bio-monitoring data show that PBDE concentrations have increased rapidly in the bodies of wildlife and human over the last few decades. Based on the studies on experimental animals, the toxicological endpoints of exposure to PBDEs are likely to be thyroid homeostasis disruption, neuro-developmental deficits, reproductive ineffectiveness and even cancer. Unfortunately, the available molecular toxicological evidence for these endpoints is still very limited. This review focuses on the recent studies on the molecular mechanisms of PBDE toxicities carried out through the hormone receptor pathways, including thyroid hormone receptor, estrogen receptor, androgen receptor, progesterone receptor and aryl hydrocarbon receptor pathways. The general approach in the mechanistic investigation is to examine the in vitro direct binding of a PBDE with a receptor, the in vitro recruitment of a co-activator or co-repressor by the ligand-bound receptor, and the participation of the ligand in the receptor-mediated transcription pathways in cells. It is hoped that further studies in this area would provide more insights into the potential risks of PBDEs to human health.

Development of redox-labeled electrochemical immunoassay for polycyclic aromatic hydrocarbons with controlled surface modification and catalytic voltammetric detection

A redox-labeled direct competitive electrochemical immunoassay for polycyclic aromatic hydrocarbons (PAHs) was developed. A ruthenium tris(bipyridine)-pyrenebutyric acid conjugate was synthesized as the redox-labeled tracer. Its recognition by an anti-PAH monoclonal antibody was confirmed by surface plasmon resonance. In the immunoassay, the antibody was immobilized on (3-glycidoxypropyl)-trimethoxysilane (GPTMS)-modified indium tin oxide (ITO) electrodes. The assay was quantified by measuring the electro-catalytic current of the redox label in an oxalate-containing electrolyte which served as a sacrificial electron donor to amplify the current signal. Formation of GPTMS film on ITO and subsequent antibody immobilization were characterized by X-ray photoelectron spectroscopy (XPS) and electrochemistry. Using a ruthenium tris(bipyridine)-conjugated IgG (IgG-Ru) as the surface-bound redox probe, the highest electrochemical signal was obtained on GPTMS electrodes with 1 h modification. Under the optimized conditions for ITO modification, antibody immobilization and tracer concentration, competition curves for benzo[a]pyrene and pyrenebutyric acid were obtained with a detection limit of 2.4 and 10 ng mL(-1), respectively. The redox-labeled electrochemical immunoassay with signal amplification mechanism offers a potential analytical method for the simultaneous detection of multiple environmental organic pollutants on antibody biochips.