Linghao He

Modification of polymorphisms in polyvinylidene fluoride thin films via water and hydrated salt

In this study, the effects of solvent and magnesium chloride hexahydrate (MgCl2·6H2O) on the polymorphism of polyvinylidene fluoride (PVDF) thin films were systematically investigated. Wherein, N,N-dimethylformamide (DMF) and water with different volume ratio were used as mixed solvents to obtain the solution casting films, P series. In addition, MgCl2·6H2O was comparatively added to prepare PVDF/MgCl2·6H2O hybrid films, P-M series. Fourier transform infrared spectroscopy (FT-IR), X-ray diffraction (XRD), and differential scanning calorimeter (DSC) were utilized to study the influence of the water content in the mixed solvents and the hydrated salt on crystallization behavior of PVDF. Further, the morphologic images from scanning electronic microscopy (SEM) and polarized optical microscopy (POM), as well as the pizoelectirc d33 test also supplies the corresponding evidences. As indicated, the water in the mixed solvent shows different effect on main crystal forms of PVDF. At low water content, the solvents may favor the polar phase (β- and γ-phase) mainly by hydrogen bonds interactions between PVDF and water, together with dipolar interactions between PVDF and DMF. At high water content, the nonsolvent water will impose confinement effect on polymer chain diffusion and crystal growth which facilitate the formation of α-phase PVDF. Moreover, magnesium chloride hexahydrate mainly functioned as the nucleation sites for PVDF crystallization. The result of small-angle X-ray scattering (SAXS) implies the content of water or MgCl2·6H2O has little impact on the structure of the long period.

Modification of Carbon Nanotubes Using Poly(vinylidene fluoride) with Assistance of Supercritical Carbon Dioxide: The Impact of Solvent

We report herein a typical piezoelectric polymer, poly(vinylidene fluoride) (PVDF) to be successfully wrapped on single-walled carbon nanotubes (SWCNTs) using a simple supercritical carbon dioxide (SC CO(2)) antisolvent-induced polymer epitaxy method. Our study focused on the effect of different solvents on the morphology of PVDF wrapping on SWCNTs. Three organic solvents, dimethyl sulfoxide (DMSO), N,N-dimethylformamide (DMF), and N,N-dimethylacetamide (DMAc) were chosen for PVDF. When DMSO was used as solvent, the decorating degree of PVDF on the surface of SWCNTs increases significantly with the increase of SC CO(2) pressure, and nanocrystals wrapping on SWCNTs can be observed at high pressure. FTIR and Raman spectra indicated that there exist interactions between SWCNTs and PVDF chains. Whats more, FTIR results also show that there exists a transformation from the beta-phase to the alpha-phase of PVDF in DMSO with the assistance of SC CO(2), which is similar to the action of elongation/shear flow field. It indicated that the alpha-phase is the predominant form occurring on the surface of SWCNTs after treatment with SC CO(2). And the helical structure on SWCNTs observed from the TEM image reflected the alternate trans- and gauche-bond conformation of the alpha-form. When DMF or DMAc was used as the solvent, although nanocrystal wrapping and helical structure was not visible, the samples had more excellent dispersion than that in DMSO. Particularly, for DMF, a typical network structure was observed, which is similar to a spider web. Therefore, this work supplies a clue that the various morphologies of nanohybrid structure can be obtained just by changing the solvent during the treatment process of SC CO(2), and accordingly, the tailored nanohybrid structure are promising and important for functional design as a basic component in microfabrication and other fields.

Label-free aptamer biosensor for thrombin detection on a nanocomposite of graphene and plasma polymerized allylamine

A label-free and effective aptasensor based on an amino-functionalized nanocomposite of graphene and plasma-polymerized allylamine (G-PPAA) was developed for thrombin detection. Graphene was assembled on the substrate, followed by the self-assembly of octadecylamine (OTA) to protect the graphene from etching by subsequent plasma irradiation. Afterward, PPAA was deposited onto the graphene surface with the self-assembled OTA, and the nanocomposite with amino groups was fabricated. The label-free thrombin aptamer was immobilized onto the amino-functionalized nanocomposite matrix via electrostatic interaction between the phosphate groups of the aptamer and the amino groups in PPAA. The process was investigated using impedimetric detection and a quartz crystal microbalance (QCM). The chemical compositions, surface morphology, and electrochemical properties were found to be dependent on the plasma conditions used in the polymer deposition. The amounts and kinetics of aptamer immobilization and thrombin detection were determined using QCM measurements. A relatively high affinity constant of aptamer immobilization and low detection limit for thrombin were achieved by using the G-PPAA film as the biosensor matrix. Results suggest that G-PPAA films can be applied in gene therapy and protein detection.

Modification of Graphene Oxide with Amphiphilic Double-Crystalline Block Copolymer Polyethylene-b-poly(ethylene oxide) with Assistance of Supercritical CO2 and Its Further Functionalization

Graphene oxide (GO) sheets were noncovalently modified with an amphiphilic double-crystalline block copolymer, polyethylene-b-poly(ethylene oxide) (PE-b-PEO) with assistance of supercritical CO(2) (SC CO(2)) in this work. The resulting PE-b-PEO/GO nanohybrids were characterized by transmission electron microscopy (TEM), wide-angle X-ray diffraction (WAXD), Fourier transform infrared spectroscopy (FTIR), and Raman spectra. Distinct morphologies of PE-b-PEO decorating on the surface of GO were obtained in different solvent systems and at different SC CO(2) pressures. We found that the solvent system and the SC CO(2) have significant influence on the crystallization, aggregation, or assembly behaviors of PE-b-PEO molecular chains on the GO sheets. The formation mechanism of the distinct nanohybrid structures is attributed to a relevant easy heteronucleation and the limited crystal growth of the block polymer on the surface of GO. The resulting modified GO sheets could find a broad spectrum of applications not only in producing graphene-based nanocomposites but also being used as a template to fabricate multifunctional structures due to the unique properties of PE-b-PEO. As a proof-of-concept, we further decorated the GO sheets with the as-prepared Au nanoparticles (Au NPs) and CdTe nanoparticles (CdTe NPs) with PE-b-PEO as the interlinker. Using the thiol-terminated PE-b-PEO as an interlinker, Au NPs can be densely assembled on the surface of GO via robust Au-S bonds. Furthermore, the photoluminescence quenching of CdTe NPs was more notable for PE-b-PEO/GO-CdTe hybrid compared to the GO-CdTe hybrid, suggesting that the electron transfer from the CdTe NPs to the GO sheets was enhanced with the PE-b-PEO interlinker. The availability of these affordable graphene-based multifunctional structures and their fundamental properties will open up new opportunities for nanoscience and nanotechnology and accelerate their applications.

Enhancement of β-crystalline phase of poly(vinylidene fluoride) in the presence of hyperbranched copolymer wrapped multiwalled carbon nanotubes.

Many efforts have been performed on the poly(vinylidene fluoride), PVDF, due to its piezoelectric, pyroelectric and ferroelectric potentials. In this regard, how to fabricate the PVDF with high content of β-phase, which is also the direct contribution to PVDFs prominent property, becomes a critical issue. In this study, starting with the α-phase dominated sample, the PVDF with extremely high content of β-crystalline phase was obtained by the incorporation of multiwalled carbon nanotubes (MWCNTs) modified by hyperbranched copolymers (HBCs). We proved that, via XRD, DSC as well as the structural characterizations from the polarized optical microscopy and transmission electron microscopy (TEM), the success of this strategy was ascribed to the enhanced dispersibility and stability of MWCNTs endowed by the HBCs, which significantly favors the formation of the β-crystalline phase of PVDF.

THE STRUCTURE AND PROPERTIES OF CHITOSAN/POLYETHYLENE GLYCOL/SILICA TERNARY HYBRID ORGANIC-INORGANIC FILMS *

The ternary hybrid films consisting of chitosan (CS), polyethylene glycol (PEG) and nano-sized silica which was surface-modified by amino groups (RNSA) were prepared. The structures of the blend membranes were characterized by attenuation total reflection-infrared spectroscopy (ATR-IR), X-ray diffraction (XRD), optical microscopy (OM) and differential scanning calorimetry (DSC). The results showed that the addition of silica affected not only the distribution and crystallinity of PEG on the sample surface, but also the phase coarseness and the crystalline structure of chitosan in the blend system. Moreover, PEG changed the crystalline structure of chitosan. Upon annealing (at 100°C for 1 h), the blends would show the altered crystalline structure of chitosan, the reinforced phase coarseness, as well as the decreased miscibility and interaction between chitosan and PEG.

Fe(III)-based metal–organic framework-derived core–shell nanostructure: Sensitive electrochemical platform for high trace determination of heavy metal ions

A new core-shell nanostructured composite composed of Fe(III)-based metal-organic framework (Fe-MOF) and mesoporous Fe3O4@C nanocapsules (denoted as Fe-MOF@mFe3O4@mC) was synthesized and developed as a platform for determining trace heavy metal ions in aqueous solution. Herein, the mFe3O4@mC nanocapsules were prepared by calcining the hollow Fe3O4@C that was obtained using the SiO2 nanoparticles as the template, followed by composing the Fe-MOF. The Fe-MOF@mFe3O4@mC nanocomposite demonstrated excellent electrochemical activity, water stability and high specific surface area, consequently resulting in the strong biobinding with heavy-metal-ion-targeted aptamer strands. Furthermore, by combining the conformational transition interaction, which is caused by the formation of the G-quadruplex between a single-stranded aptamer and high adsorbed amounts of heavy metal ions, the developed aptasensor exhibited a good linear relationship with the logarithm of heavy metal ion (Pb2+ and As3+) concentration over the broad range from 0.01 to 10.0nM. The detection limits were estimated to be 2.27 and 6.73 pM toward detecting Pb2+ and As3+, respectively. The proposed aptasensor showed good regenerability, excellent selectivity, and acceptable reproducibility, suggesting promising applications in environment monitoring and biomedical fields.

Carbon-based nanocomposites with aptamer-templated silver nanoclusters for the highly sensitive and selective detection of platelet-derived growth factor

We synthesized two kinds of carbon-based nanocomposites of silver nanoclusters (AgNCs). An aptamer for targeted platelet-derived growth factor-BB (PDGF-BB) detection was used as the organic phase to produce AgNCs@Apt, three dimensional reduced graphene oxide@AgNCs@Aptamer (3D-rGO@AgNCs@Apt), and graphene quantum dots@AgNCs@Aptamer (GQD@AgNCs@Apt) nanocomposites. The formation mechanism of the developed nanocomposites was described by detailed characterizations of their chemical and crystal structures. Subsequently, the as-synthesized nanoclusters containing aptamer strands were applied as the sensitive layers to fabricate a novel electrochemical aptasensor for the detection of PDGF-BB, which may be directly used to determine the target protein. Electrochemical impedance spectra showed that the developed 3D-rGO@AgNCs@Apt-based biosensor exhibited the highest sensitivity for PDGF-BB detection among three kinds of fabricated aptasensors, with an extremely low detection limit of 0.82pgmL-1. In addition, the 3D-rGO@AgNCs@Apt-based biosensor showed high selectivity, stability, and applicability for the detection of PDGF-BB. This finding indicated that the AgNC-based nanocomposites prepared by a one-step method could be used as an electrochemical biosensor for various detection procedures in the biomedical field.

An electrochemical sensor based on rhodamine B hydrazide-immobilized graphene oxide for highly sensitive and selective detection of Cu(II)

A novel strategy for fabricating a Cu2+ sensor based on rhodamine B hydrazide (RBH)-immobilized graphene oxide (GO) was reported. The thiol-modified Au electrode was functionalized by carboxyl functionalized GO through intermolecular interactions, followed by chemical bonding with RBH. The developed nanocomposite was used as an electrochemical sensor for detecting Cu2+ in aqueous solution using electrochemical impedance spectroscopy analysis with a detection limit of 0.061 nM within the range from 0.1 to 50 nM. Furthermore, the interference from potentially interfering ions such as Hg2+, Ag+, Cr2+, Fe2+, Pb2+, Ba2+, Mn2+, Co2+, and Ni2+ associated with Cu2+ analysis could be effectively inhibited. In addition, the developed Cu2+ sensor could be reproduced up to 10 cycles. In this approach, the fluorescent probe RBH can be replaced by other fluorescein derivatives which could identify the corresponding ions, which makes the approach a widely applicable strategy for metal ion detection.

Feasible electrochemical biosensor based on plasma polymerization-assisted composite of polyacrylic acid and hollow TiO2 spheres for sensitively detecting lysozyme

A composite made of polyacrylic acid and hollow TiO2 spheres (TiO2@PPAA) was prepared by the plasma polymerization method and subsequently used as an electrode material for detecting lysozyme. The chemical structure, surface morphology, and electrochemical performance of the TiO2@PPAA composite were mainly affected by the plasma input power used during plasma polymerization. After optimizing plasma conditions, aptamer strands exhibited high adsorption affinity toward the surface of TiO2@PPAA composite via synergistic effects between TiO2 and PPAA. Electrochemical impedance spectroscopy results showed that the developed TiO2@PPAA aptasensor presents highly sensitive detection ability toward lysozyme; the limit of detection of the proposed aptasensor is 0.015 ng mL(-1) (1.04 pM) within the range of 0.05-100 ng mL(-1) in terms of 3σ value. The film further showed excellent selectivity toward lysozyme in the presence of interfering proteins, such as thrombin, bovine serum albumin, and immunoglobulin E. Thus, this aptasensing strategy might broaden the applications of plasma polymerized nanomaterials in the field of biomedical research and early clinical diagnosis.