Xiaojun Han

Hydrodynamically driven self-assembly of giant vesicles of metal nanoparticles for remote-controlled release.

The hydrodynamics of laminar flow in a microfluidic device has been used to control the continuous self-assembly of gold nanoparticles (NPs) tethered with amphiphilic block copolymers. Spherical micelles, giant vesicles (500 nm-2.0 μm), or disk-like micelles could be formed by varying the flow rates of fluids. Such vesicles can release encapsulated hydrophilic species by using near-IR light.

Electric field-induced synthesis of dendritic nanostructured α-Fe for electromagnetic absorption application

In this work, large-scale three-dimensional dendritic α-Fe which possesses two different faces with uniform width of about 3.0 μm and length of about 9.0 μm was directly synthesized using an electric field-induced and electrochemical reduction method in FeSO4 aqueous solution for the first time. This synthesis method shows great advantages including environment-friendliness, extremely low cost and high efficiency. The specific dendritic structure was induced to grow along three of six 〈110〉 crystallographically equivalent directions under a symmetrical electric field. The uniform length of the dendritic α-Fe is subject to Fe2+ concentration gradient. The investigation of the magnetic properties and electromagnetic absorbability indicates that this kind of dendritic α-Fe exhibits both high absorption efficiency with the minimum reflection loss value of −32.3 dB and a broad absorption band up to 12 GHz. The dendritic α-Fe could be an extremely promising electromagnetic absorption material.

Continuous Microfluidic Self-Assembly of Hybrid Janus-Like Vesicular Motors: Autonomous Propulsion and Controlled Release

A microfluidic strategy is developed for the continuous fabrication of hybrid Janus vesicular motors that uniquely combine the capability of autonomous propulsion and externally controlled delivery of encapsulated payload.

Vesicular self-assembly of colloidal amphiphiles in microfluidics.

Hydrodynamic flow in a microfluidic (MF) device offers a high-throughput platform for the continuous and controllable self-assembly of amphiphiles. However, the role of hydrodynamics on the assembly of colloidal amphiphiles (CAMs) is still not well understood. This Article reports a systematic study of the assembly of CAMs, which consist of Au nanoparticles (AuNPs) grafted with amphiphilic block copolymers, into vesicles with a monolayer of CAMs in the membranes using laminar flows in MF flow-focusing devices. Our experimental and simulation studies indicate that the transverse diffusion of solvents and colloids across the boundary of neighboring lamellar flows plays a critical role in the assembly of CAMs into vesicles. The dimension of the vesicles can be controlled in the range of 100-600 nm by tuning the hydrodynamic conditions of the flows. In addition, the diffusion coefficient of CAMs was also critical for their assembly. Under the same flow conditions, larger CAMs generated larger assemblies as a result of the reduced diffusion rate of large amphiphiles. This work could provide fundamental guidance for the preparation of nanoparticle vesicles with applications in bioimaging, drug delivery, and nano- and microreactors.

Electroformation of giant unilamellar vesicles using interdigitated ITO electrodes

A coplanar interdigitated electrode was used as a new electrode system to form giant unilamellar vesicles (GUVs). The formation of GUVs using interdigitated electrodes was investigated in detail with respect to various parameters, including solution height, electrode width, the amplitude and frequency of AC fields, and temperature. Interdigitated electrodes with smaller widths generated bigger GUVs under the same conditions. According to both experimental and 3D field simulation results, a solution height above 600 μm has no influence on the GUV formation. GUVs were obtained within a wide range of frequency from 1 Hz to 104 Hz and field amplitude from 1 V to 10 V. The diameters of the GUVs decreased with increasing frequency at a constant amplitude, and increased with increasing amplitude from 1 V to 5 V and then decreased from 5 V to 10 V at 10 Hz. A phase diagram based on varying the AC frequency and amplitude was obtained experimentally, which can be used to predict the electroformation of GUVs.

Lipid nanotube formation using space-regulated electric field above interdigitated electrodes.

Lipid nanotubes have great potential in biology and nanotechnology. Here we demonstrate a method to form lipid nanotubes using space-regulated AC electric fields above coplanar interdigitated electrodes. The AC electric field distribution can be regulated by solution height above the electrodes. The ratio of field component in x axis (Ex) to field component in z axis (Ez) increases dramatically at solution height below 50 μm; therefore, at lower solution height, the force from Ex predominantly drives lipids to form lipid nanotubes along with the electric field direction. The forces exerted on the lipid nanotube during its formation were analyzed in detail, and an equation was obtained to describe the relationship among nanotube length and field frequency, amplitude, and time. We believe that the presented approach opens a way to design and prepare nanoscale materials with unique structural and functional properties using space-regulated electric fields.

Polydopamine-coated liposomes as pH-sensitive anticancer drug carriers.

Abstract Stimuli-responsive drug carriers are considered to play important roles in chemotherapy. We fabricated pH-sensitive polydopamine-protected liposomes (liposome@PDA) drug delivery systems, which were characterised with microscope, scanning electron microscope (SEM), UV-vis spectrometer and Fourier transform infrared (FTIR) technieques. The typical chemotherapeutic agent, 5-fluorouracil (5-FU), was loaded into liposome@PDA capsules. The maximum release percentages of 5-FU are 3.2%, 29.5%, 52.7%, 76.7% in the solution with pH 7.42, 6.87, 4.11 and 3.16, respectively. The in vitro cell cytotoxity experiments were carried out using 5-FU-loaded capsules at pH 6.87 solution, which simulate the true pH around cancerous cells. At 1.5 μM concentration, the free 5-FU, 5-FU-loaded liposome capsules and 5-FU-loaded capsules showed the cell viability of 50.56%, 22.66% and 21.63%, respectively. It confirms that drug-loaded capsules performed better than free drug. The results demonstrate the great potential of liposome@PDA capsules as carriers in biomedical applications.

Interactions of the baicalin and baicalein with bilayer lipid membranes investigated by cyclic voltammetry and UV-Vis spectroscopy.

The baicalin and baicalein are the major flavonoids found in Radix Scutellariae, an essential herb in traditional Chinese medicine for thousands of years. The interactions of the baicalin and baicalein with lipid bilayer membranes were studied using cyclic voltammetry and UV-Vis spectroscopy. The thickness d of supported bilayer lipid membranes was calculated as d=4.59(±0.36) nm using AC impedance spectroscopy. The baicalein interacted with egg PC bilayer membranes in a dose-dependent manner. The responses of K3Fe(CN)6 on lipid bilayer membrane modified Pt electrode linearly increased in a concentration range of baicalein from 6.25μM to 25μM with a detection limit of 0.1μM and current-concentration sensitivity of 0.11(±0.01) μA/μM, and then reached a plateau from 25μM to 50μM. However the baicalin showed much weaker interactions with egg PC bilayer membranes. UV-Vis spectroscopy also confirmed that the baicalein could interact with egg PC membranes noticeably, but the interaction of baicalin with membranes was hard to be detected. The results provide useful information on understanding the mechanism of action of Radix Scutellariae in vivo.

Electrochemiluminescent TiO2/CdS nanocomposites for efficient immunosensing of HepG2 cells

An electrochemiluminescence (ECL) immunosensor for HepG2 cells (human liver hepatocellular carcinoma cells) was fabricated based on CdS-capped TiO2 hybrid nanoparticles. The CdS-capped TiO2 was obtained by immersing TiO2 nanoparticles into separate Cd2+ and S2- solutions successively 10 times. The hybrid nanoparticles have excellent ECL intensity after coating with 1-ethyl-3-methylimidazolium tetrafluoroborate ionic liquid (IL) and 3-aminopropyl-triethoxysilane (APTES). The viscous IL is helpful to immobilize the hybrid nanoparticles on the electrode as well as for the electron transfer from nanoparticles to the electrode, which is advantageous to the ECL immunosensor. APTES was used to attach gold nanoparticles onto the electrode surface. The HepG2 antibodies were then immobilized onto the electrode surface via the interaction between their amine groups and gold nanoparticles. A wide detection range from 400 to 10 000 cells per mL was achieved. The detection limit was determined to be 396 cells per mL. Using HeLa cells as interferences, the excellent selectivity of this sensor has been demonstrated using both confocal fluorescence microscopy and ECL techniques. Due to its good sensitivity, selectivity and stability, the sensor has great potential in medical diagnosis.

Electroformation of giant unilamellar vesicles in saline solution.

Giant unilamellar vesicle (GUV) formation on indium tin oxide (ITO) electrodes in saline solution and from charged lipids has proven to be difficult in the past. Yet the best cell membrane models contain charged lipids and require physiological conditions. We present a way to overcome this problem by using plasma cleaned ITO electrodes. GUVs from zwitterionic lipids, lipid mixtures and even pure charged lipids could be electroformed under physiological conditions and even higher concentrations of NaCl. The hydrophilic ITO surface may facilitate the hydration of the solid lipid film and the formation of lipid bilayers that subsequently bend and form vesicles. The formation of GUVs in saline solution is influenced by different parameters. The influences of the amplitude and frequency of the used AC field, the NaCl concentration, and the temperature were investigated. Finite element analysis simulating the effect of the electric field on GUV formation in saline solution could well explain the experimental results. Frequencies in the kHz-range favored for GUVs formation in saline solution, as they suppress the formation of electric double layer, while higher frequencies could again impair the effect of electric field and impede GUV formation. The diameters of the GUVs increased gradually with NaCl concentration from 0mM to 200mM and subsequently decreased from 200mM to 2M. High yields of GUVs were also formed in PBS solution and cell culture medium, which indicates this method is a promising way to prepare GUVs on a large scale in physiological relevant conditions.