Xiaoyuan Zhang

Fabrication, characterization and sensor application of electrospun polyurethane nanofibers filled with carbon nanotubes and silver nanoparticles

We reported here the electrospinning preparation of polyurethane nanofibers filled with carbon nanotubes and silver nanoparticles (PU-MWCNT-AgNP) and the subsequent fabrication of a novel non-enzymatic amperometric biosensor for analytical determination of hydrogen peroxide. The morphologies of the as-spun PU-MWCNT-AgNP hybrid nanofibers were observed by scanning and transmission electron microscopy. The interaction between MWCNTs and AgNPs in the electrospun nanofibers was studied by differential scanning calorimetry and dynamic mechanical analysis. The cyclic voltammetry experiments indicate that PU-MWCNT-AgNP nanofiber modified electrodes have high electrocatalytic activity on hydrogen peroxide, and the chronoamperometry measurements illustrate that this electrospun sensor has high sensitivity for detecting hydrogen peroxide. Our study further confirms the remarkable synergistic effect of MWCNTs and AgNPs on the significant improvement of the conductivity of electrospun nanofibers and the electrocatalytic activity, as well as the sensitivity of the fabricated non-enzymatic sensor. Under an optimal experimental condition, the created biosensor for detecting hydrogen peroxide has a sensitivity of 160.6 μA mM-1 cm-2, a wide linear range from 0.5 to 30 mM and a detection limit of 18.6 μM (S/N = 3), which indicates that this novel and simple strategy for fabricating electrochemical sensor by an electrospinning technique has wide potential applications in bio-analysis and detection.

Synthesis, characterization and drug release application of carbon nanotube-polymer nanosphere composites

We report here a successful in situ synthesis of block copolymer nanospheres (CPNS) on the side-walls of multi-walled carbon nanotubes (MWCNTs) to create functional nanomaterials. The thermo-sensitive CPNS with an average size of about 100 nm were created along MWCNTs by an one-pot atom transfer radical polymerization reaction with poly(ethylene oxide) macromonomer and N-isopropylacrylamide monomer. The synthesized MWCNT-CPNS nanocomposites were characterized and confirmed by FT-IR, 1H NMR, and Raman spectroscopy. The amount of grafted polymers on MWCNTs was measured by TGA. The formation of CPNS along the side-walls of MWCNTs was observed and identified by TEM. Furthermore, the newly-created MWCNT-CPNS nanocomposites were used as novel carriers for controlled anticancer drug (adriamycin) release. The obtained results indicate that the release amount of drugs varied greatly below and above the lower critical solution temperature (LCST) of the used thermo-sensitive polymer, and therefore the synthesized MWCNT-CPNS nanocomposites can be used as a kind of potential candidate for drug delivery and release. We expect the novel thermo-sensitive nanocomposites based on MWCNTs and CPNS will have wider applications in in vivo targeted drug delivery and release.

Pathway mediated microstructures and phase morphologies of asymmetric double crystalline co-oligomers

Various microstructures and phase morphologies of an amphiphilic poly(ethylene oxide)-block-polyethylene (PEO-b-PE) co-oligomer, controlled by topological restriction of PE segments on the tethered PEO chains, were characterized by differential scanning calorimetry (DSC), polarized optical microscopy (POM), scanning electron microscopy (SEM), and synchrotron radiation wide-angle/small-angle X-ray scattering (WAXS/SAXS) in drop-cast films. The crystallization processes were mediated by two pathways, a one-step crystallization process (I) and a sequential crystallization process (II). Results show that the thermal procedures have great influence on the microstructures and phase morphologies of PEO-b-PE co-oligomer, e.g., negative spherulites with radial stripes were detected in the one-step crystallization process (I), while crystalline texture, which contains a large number of crystals with reduced sizes, formed in the sequential crystallization process (II). Based on our experimental data, the topological restriction effect encountered by PEO chains depends on the hard confinement of PE crystals and the soft confinement of amorphous PE in the two crystallization procedures. The formation mechanisms of the long-range order structures within the co-oligomer were elucidated through morphology models. These nano-patterned structures make the double crystalline block copolymers outstanding candidates for surface modification, micromolding, and optoelectronic devices in nanotechnological and biomedical applications.

Nanoconfinement and Sansetsukon-like Nanocrawling Govern Fibrinogen Dynamics and Self-Assembly on Nanostructured Polymeric Surfaces

Surface nanostructures are increasingly more employed for controlled protein assembly on functional nanodevices, in nanobiotechnology, and in nanobiomaterials. However, the mechanism and dynamics of how nanostructures induce order in the adsorbed protein assemblies are still enigmatic. Here, we use single-molecule mapping by accumulated probe trajectories and complementary atomic force microscopy to shed light on the dynamic of in situ assembly of human plasma fibrinogen (HPF) adsorbed on nanostructured polybutene-1 (PB-1) and nanostructured polyethylene (PE) surfaces. We found a distinct lateral heterogeneity of HPF-polymer nanostructure interface (surface occupancy, residence time, and diffusion coefficient) that allow identifying the interplay between protein topographical nanoconfinement, protein diffusion mechanism, and ordered protein self-assembly. The protein diffusion analysis revealed high-diffusion polarization without correlation to the anisotropic friction characteristic of the polymer surfaces. This suggests that HPF molecules confined on the nanosized PB-1 needle crystals and PE shish-kebab crystals, respectively, undergo partial detachment and diffuse via a Sansetsukon-like nanocrawling mechanism. This mechanism is based on the intrinsic flexibility of HPF in the coiled-coil regions. We conclude that nanostructured surfaces that encourage this characteristic surface mobility are more likely to lead to the formation of ordered protein assemblies and may be useful for advanced nanobiomaterials.