Shenghua Ma

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.

Palladium Nanotubes Formed by Lipid Tubule Templating and Their Application in Ethanol Electrocatalysis

Palladium nanotubes were fabricated by using lipid tubules as templates for the first time in a controlled manner. The positively charged lipid 1,2-dioleoyl-3-trimethylammoniumpropane (DOTAP) was doped into lipid tubules to adsorb PdCl4 (2-) on the tubule surfaces for further reduction. The lipid tubule formation was optimized by studying the growing dynamics and ethanol/water ratio. The DOTAP-doped tubules showed pH stability from 0 to 14, which makes them ideal templates for metal plating. The Pd nanotubes are open-ended with a tunable wall thickness. They exhibited good electrocatalytic performance in ethanol. Their electrochemically active surface areas were 6.5, 10.6, and 83.2 m(2)  g(-1) for Pd nanotubes with 77, 101, and 150 nm wall thickness, respectively. These Pd nanotubes have great potential in fuel cells. The method demonstrated also opens up a way to synthesize hollow metal nanotubes.

High impedance droplet-solid interface lipid bilayer membranes.

A droplet-solid interface lipid bilayer membrane (DSLM) with high impedance was developed through controlling the contact area between an aqueous droplet and electrode. The electrode size can be easily controlled from millimeter to micrometer level. The droplet-solid interface lipid bilayer membranes were characterized by cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS), and fluorescence microscopy. The fluorescence recovery after photobleaching (FRAP) was applied to determine the diffusion coefficient of egg PC DSLM to be 2.58 μm(2) s(-1). The DSLM resistance can reach up to 26.3 GΩ, which was then used to study the ion channel behavior of melittin. The resistivity of the bilayer membrane decreased linearly with the increase of melittin concentration in the membrane. The high impedance and fluidity of DSLM makes it an ideal model cell membrane system for ion channel study and high-throughput drug screening.

Magnetically triggered drug release from biocompatible microcapsules for potential cancer therapeutics

This paper demonstrates that magnetic field triggered drug release from magnetic lipid microcapsules (MLMs) in a controlled manner. Two types of MLMs were fabricated, i.e., MLMs with negatively charged magnetic nanoparticles (MNPs) inside and MLMs with positively charged MNPs on their surfaces. The release of carboxyfluorescein (CF) and the chemotherapy drug doxorubicin (Dox) induced by the AC magnetic field (AMF) was investigated in detail both experimentally and theoretically. Although the drug release of these two types of MLMs synchronizes the switch of the AMF, they exhibited different mechanisms. The magnetic heating effect dominates the release of MLMs with MNPs inside, while both magnetic heating and oscillation effects play important roles in the release of MLMs with MNPs on the surfaces. The in vitro cytotoxicity experiments of Dox loaded microcapsules toward HeLa cells were further performed, which confirmed that these magnetic responsive drug carriers had obvious effects on cell death triggered by the external non-invasive AMF.

Fabrication of pH sensitive microcapsules using soft templates and their application to drug release

A method based on soft templates for pH sensitive microcapsule fabrication was developed using a layer-by-layer assembly technique. Toluene-in-water emulsion droplets were first stabilized by a surfactant sodium dodecyl benzene sulfonate (SDBS). Poly(diallyldimethyl ammonium chloride) modified latex beads were then adsorbed onto the droplet surfaces to make the emulsion more rigid. PSS (poly(sodium 4-styrenesulfonate))/PDDA (poly(diallyldimethyl ammonium chloride)) was assembled alternately onto the emulsion surface to form the microcapsules. Zeta potential analyzer, scanning electron microscopy (SEM), transmission electron microscopy (TEM), FT-IR, and fluorescence microscopy were used to characterize the samples. The toluene droplet templates were removed by ethanol upon heating. Fluorescein, as the water-soluble model drug, was loaded into the microcapsules. Its release behaviors were investigated as a function of wall thickness and pH. The maximum release percentage 61% was obtained after 36 hours at 37 °C at pH 7 with one double layer capsule. The capsule itself is nontoxic, while 5-fluorouracil (5-FU) loaded capsules killed 64.18% SK-RC-2 cells at a concentration of 17 μM at pH 7, which shows the great potential of this type of microcapsule in cancer chemotherapy. Olive oil and liquid paraffin were used to replace the toluene for forming soft templates in order to obtain microcapsules which are suitable for loading hydrophobic drugs. Sudan-1 was chosen as a hydrophobic model drug and 25% release was obtained after 36 hours at 37 °C.

Inorganic microcapsules mineralized at the interface of water droplets in ethanol solution and their application as drug carriers

This paper reported a crystallization – dissolution – interface mineralization (CDIM) method on synthesizing calcium carbonate (CaC) and calcium phosphate (CaP) inorganic microcapsules with good biocompatibility and good pH sensitivity. The method is based on mineralization at the ethanol/water interface. The microcapsules were formed in a few seconds and did not need post treatment for removing the templates. The diameters of the microcapsules can be controlled by the size of the crystal clusters regulated by stirring time. Carboxyfluorescein (CF) molecules as model drugs were encapsulated inside the capsules after coating with FeIII–polyphenol tannic acid (TA) films. The pH sensitive carboxyfluorescein molecule releasing behavior was investigated. The lower pH caused faster and thorough release of CF. The CDIM method can be applied for fabricating other inorganic microcapsules, which holds great potential for drug delivery.

A Universal Approach for the Reversible Phase Transfer of Hydrophilic Nanoparticles

The ability to engineer the surface properties of magnetic nanoparticles is important for their various applications, as numerous physical and chemical properties of nanoscale materials are seriously affected by the chemical constitution of their surfaces. For some specific applications, nanoparticles need to be transferred from a polar to a nonpolar environment (or vice versa) after synthesis. In this work we have developed a universal method for the phase transfer of magnetic nanoparticles that preserves their shape and size. Octadecyltrimethoxysilane was used to cap the surfaces of the aqueous magnetic nanoparticles, thereby allowing their transfer into nonpolar solution. The resulting hydrophobic magnetic nanoparticles were transferred back into aqueous solution by subsequently covering them with an egg-PC lipid monolayer. The superparamagnetic properties of the particles were retained after the phase transfer. The maximum transfer yields are dependent on their particle size with a maximum value of 93.16 ± 4.75% for magnetic nanoparticles with a diameter of 100 nm. The lipid-modified magnetic particles were stable over 1 week, and thus they have potential applications in the field of biomedicine. This work also provides a facile strategy for the controllable engineering of the surface properties of nanoparticles.

Lipid membrane formation on chemical gradient modified surfaces

The relationship between surface wetting properties and lipid membrane status formed via giant unilamellar vesicle rupture was investigated using chemical gradient surfaces. Fluorescence microscopy and AFM analysis confirmed that GUVs could form uniform monolayers, monolayer patches and bilayer patches on surface regions with contact angles ranging from 108° to ∼61°, ∼60° to ∼55° and less than 5°, respectively. The intact GUVs stand in the area with contact angle between ∼54° and ∼28°.

Fabrication of Thickness-Controllable Micropatterned Polyelectrolyte-Film/Nanoparticle Surfaces by Using the Plasma Oxidation Method.

We have demonstrated a novel way to form thickness-controllable polyelectrolyte-film/nanoparticle patterns by using a plasma etching technique to form, first, a patterned self-assembled monolayer surface, followed by layer-by-layer assembly of polyelectrolyte-films/nanoparticles. Octadecyltrimethoxysilane (ODS) and (3-aminopropyl)triethoxysilane (APTES) self-assembled monolayers (SAMs) were used for polyelectrolyte-film and nanoparticle patterning, respectively. The resolution of the proposed patterning method can easily reach approximately 2.5 μm. The height of the groove structure was tunable from approximately 2.5 to 150 nm. The suspended lipid membrane across the grooves was fabricated by incubating the patterned polyelectrolyte groove arrays in solutions of 1,2-dioleoyl-sn-glycero-3-phosphocholine (DOPC) giant unilamellar vesicles (GUVs). The method demonstrated here reveals a new path to create patterned 2D or 3D structures.