Xizeng Feng

Fabrication of mesoporous silica-coated CNTs and application in size-selective protein separation

In this study, we report a simple method to coat mesoporous silica onto carbon nanotubes (CNTs) via a two-step procedure. Mesoporous CNTs@SiO2 composites have been obtained by extracting cetyltrimethylammonium bromide (CTAB) via an ion-exchange procedure after silica-coated carbon nanotubes were synthesized with the aid of the cationic surfactant CTAB. The coating process was explicitly investigated, and a possible formation mechanism of the mesoporous CNTs@SiO2 was proposed, which reveals that the ratio of CTAB/CNTs plays a critical role in the coating process. Furthermore, the pore size of the as-prepared mesoporous silica could be exactly controlled by using different amounts of the bromide surfactant CTAB. The obtained mesoporous CNTs@SiO2 composite nanomaterial was evaluated with three typical proteins, cytochrome c (Cyt c), bovine serum albumin (BSA) and lysozyme (Lyz), with different molecular sizes. The adsorption and desorption of binary mixtures of Cyt c and BSA, Cyt c and Lyz, and a ternary mixture of Cyt c, BSA and Lyz showed that the mesoporous CNTs@SiO2 are effective and highly selective adsorbents for Cyt c. The as-prepared mesoporous CNTs@SiO2 composites have shown effective performance in size-selective adsorption of biomacromolecules, demonstrating great potential in biomacromolecular separation.

Reduced Carbon Dots versus Oxidized Carbon Dots: Photo- and Electrochemiluminescence Investigations for Selected Applications

The study of the composition, morphology, and surface structure of carbon dots (Cdots) is critical to understanding their effect on the photo- and electrochemiluminescence (PL and ECL) of Cdots in selected applications. Herein, two kinds of Cdots were prepared with 3-(3,4-dihydroxyphenyl)-L-alanine (L-DOPA) as precursor. The Cdots prepared by using a carbonization-extraction strategy have a low oxidation level and are denoted as reduced Cdots (r-Cdots). The Cdots obtained with a carbonization-oxidation process are highly oxidized and are denoted as oxidized Cdots (o-Cdots). The o-Cdots have a carbon core and oxygen-containing loose shell, but the r-Cdots consist mainly of the carbon core. Whereas r-Cdots have a strong blue PL but no apparent ECL response, o-Cdots exhibit a relatively weak PL and strong ECL emission. These properties allow for selected applications of the Cdots. The r-Cdots were used in cell imaging with their high PL emission. The o-Cdots, with their high ECL efficiencies, were selected to sense Cu(2+) with Cu(2+) -inducing ECL quenching in the o-Cdots/K2 S2 O8 system. This work provides the possibility to control the composition of Cdots for selected applications and shows a good way to characterize surface traps of Cdots because ECL is characterized by the surface-state and PL is mainly related to the core-state in Cdots.

A new hydrothermal refluxing route to strong fluorescent carbon dots and its application as fluorescent imaging agent.

Due to their unique optical and biochemical properties, the water-soluble fluorescent carbon dots (CDs) have attracted a lot of attention recently. Here, strong fluorescent carbon dots with excellent quality have been synthesized by the hydrothermal refluxing method using lactose as carbon source and tris(hydroxymethyl) aminomethane (i.e. Tris) as surface passivation reagent. This facile approach was simple, efficient, economical, green without pollution, and allows large-scale production of CDs without any post-treatment. TEM measurements showed that the resulting particles exhibited an average diameter of 1.5 nm. The obtained CDs possess small particle sizes, good stability in a wide range of pH values (pH 3.5-9.5), high tolerance of salt concentration, strong resistibility to photobleaching, and a fluorescent quantum yield up to 12.5%. The CDs were applied to optical bioimaging of HeLa cells, showing low cytotoxicity and excellent biocompatibility.

Patterning of cells on functionalized poly(dimethylsiloxane) surface prepared by hydrophobin and collagen modification

Controllable cell growth on poly(dimethylsiloxzne) (PDMS) surface is important for its potential applications in biodevices. Herein, we developed a fully biocompatible approach for patterning of cells on the PDMS surface by hydrophobin (HFBI) and collagen modification. HFBI and collagen were immobilized on the PDMS surface one after another by using copper grids as a mask. HFBI self-assembly on PDMS surface converted the PDMS surface from hydrophobic to hydrophilic, which facilitated the following immobilization of collagen. Collagen had admirable ability to support cell adhesion and growth. Consequently, the HFBI/collagen-modified PDMS surface could promote cell adhesion and growth. What is more, the native PDMS surface did not support cell adhesion and growth. Patterning of cells was achieved by directly culturing 293T cells (the human embryonic kidney cell line) on the PDMS surface patterned with HFBI/collagen. Further studies by means of gene transfection experiment in vitro showed that the patterned cells were of good bioactivities. Herein, the biocompatible preparation of cell patterns on the PDMS surface could be of many applications in biosensor device fabrication.

SiO2 nanoparticles change colour preference and cause Parkinson's-like behaviour in zebrafish

With advances in the development of various disciplines, there is a need to decipher bio-behavioural mechanisms via interdisciplinary means. Here, we present an interdisciplinary study of the role of silica nanoparticles (SiO2-NPs) in disturbing the neural behaviours of zebrafish and a possible physiological mechanism for this phenomenon. We used adult zebrafish as an animal model to evaluate the roles of size (15-nm and 50-nm) and concentration (300 μg/mL and 1000 μg/mL) in SiO2-NP neurotoxicity via behavioural and physiological analyses. With the aid of video tracking and data mining, we detected changes in behavioural phenotypes. We found that compared with 50-nm nanosilica, 15-nm SiO2-NPs produced greater significant changes in advanced cognitive neurobehavioural patterns (colour preference) and caused potentially Parkinsons disease-like behaviour. Analyses at the tissue, cell and molecular levels corroborated the behavioural results, demonstrating that nanosilica acted on the retina and dopaminergic (DA) neurons to change colour preference and to cause potentially Parkinsons disease-like behaviour.

Patterning of neural stem cells on poly(lactic-co-glycolic acid) film modified by hydrophobin

Patterning of neural stem cells (NSCs) is of great importance for its potential applications in the therapy of nerve injuries. Due to the critical requirements and the great difficulty in NSCs cultivation, developing new methods for NSCs patterning is very challenging and has progressed slowly in recent years. In this study, we reported a new method for patterning NSCs on a hydrophobin II (HFBI) modified poly(lactic-co-glycolic acid) (PLGA) film by using microcontact printing (microCP) technique. HFBI modification converted the PLGA surface from hydrophobic to hydrophilic, which should facilitate the absorption of serum on it. Serum was transferred onto the modified PLGA film by microcontact printing (microCP) to promote NSCs adhesion on the PLGA surface. Since the serum-coated PLGA surface promoted NSCs adhesion and the serum-free PLGA surface inhibited NSCs adhesion, micro-patterns of NSCs were obtained by directly culturing NSCs on the PLGA surface patterned with serum. This method allows the precise control of NSCs adhesion on the PLGA film without using the conventional cell-repellent species, which is anticipated to make great contribution in the fields of therapy of nerve injuries.

Surface modification using a novel type I hydrophobin HGFI

AbstractSurface wettability conversion with hydrophobins is important for its applications in biodevices. In this work, the application of a type I hydrophobin HGFI in surface wettability conversion on mica, glass, and poly(dimethylsiloxane) (PDMS) was investigated. X-ray photoelectron spectroscopy (XPS) and water-contact-angle (WCA) measurements indicated that HGFI modification could efficiently change the surface wettability. Data also showed that self-assembled HGFI had better stability than type II hydrophobin HFBI. Protein patterning and the following immunoassay illustrated that surface modification with HGFI should be a feasible strategy for biosensor device fabrication. FigureA hydrophobin HGFI has been applied into surface wettability conversion for protein immobilization

NHS-ester functionalized poly(PEGMA) brushes on silicon surface for covalent protein immobilization.

Poly(PEGMA) homopolymer brushes were developed by atom transfer radical polymerization (ATRP) on the initiator-modified silicon surface (Si-initiator). Through covalent binding, protein immobilization on the poly(PEGMA) films was enabled by further NHS-ester functionalization of the poly(PEGMA) chain ends. The formation of polymer brushes was confirmed by assessing the surface composition (XPS) and morphology (atomic force microscopy (AFM), scanning electronic microscopy (SEM)) of the modified silicon wafer. The binding performance of the NHS-ester functionalized surfaces with two proteins horseradish peroxidase (HRP) and chicken immunoglobulin (IgG) was monitored by direct observation. These results suggest that this method which incorporates the properties of polymer brush onto the binding surfaces may be a good strategy suitable for covalent protein immobilization.

A Novel Temperature-Responsive Polymer as a Gene Vector

A temperature-responsive polymer poly{2-(dimethylamino)ethyl methacrylate-co-[cis-butenedioic anhydride-poly[(N-isopropylacrylamide)-co-(butyl methacrylate)]]} (PDMNIB) was synthesized by free radical polymerization. The polymer had a significant temperature-responsive behavior with a lower critical solution temperature (LCST) at 20 degrees C. Gel retardation assay showed that PDMNIB could efficiently interact with DNA. Dynamic light scattering (DLS) and zeta potential measurement indicated that the average sizes and the surface electric charges of the PDMNIB/DNA complexes could be changed by temperature. Due to the thermosensitive interaction between PDMNIB and DNA, the gene transfection efficiency of PDMNIB could be improved by temperature.

Adsorption behavior of hydrophobin proteins on polydimethylsiloxane substrates.

The design of a bioactive surface with appropriate wettability for effective protein immobilization has attracted much attention. Previous experiments showed that the adsorption of hydrophobic protein HFBI onto a polydimethylsiloxane (PDMS) substrate surface can reverse the inherent hydrophobicity of the surface, hence making it suitable for immobilization of a secondary protein. In this study, atomistic molecular dynamics simulations have been conducted to elucidate the adsorption mechanism of HFBI on the PDMS substrate in an aqueous environment. Nine independent simulations starting from three representative initial orientations of HFBI toward the solid surface were performed, resulting in different adsorption modes. The main secondary structures of the protein in each mode are found to be preserved in the entire course of adsorption due to the four disulfide bonds. The relative binding free energies of the different adsorption modes were calculated, showing that the mode, in which the binding residues of HFBI fully come from its hydrophobic patch, is most energetically favored. In this favorable binding mode, the hydrophilic region of HFBI is fully exposed to water, leading to a high hydrophilicity of the modified PDMS surface, consistent with experiments. Furthermore, a set of residues consisting of Leu12, Leu24, Leu26, Ile27, Ala66, and Leu68 were found to play an important role in the adsorption of HFBI on different hydrophobic substrates, irrespective of the structural features of the substrates.