Humphrey Hak Ping Yiu

Magnetic nanoparticles for gene and drug delivery

Investigations of magnetic micro- and nanoparticles for targeted drug delivery began over 30 years ago. Since that time, major progress has been made in particle design and synthesis techniques, however, very few clinical trials have taken place. Here we review advances in magnetic nanoparticle design, in vitro and animal experiments with magnetic nanoparticle-based drug and gene delivery, and clinical trials of drug targeting.

Enzymes supported on ordered mesoporous solids: a special case of an inorganic-organic hybrid

The discovery in the late 1990s of ordered, high surface area silicas with pore sizes of 5 nm and above opened the way to the study of well-defined biomolecule–mesoporous silica hybrids. In particular, it has been possible to immobilize a range of small to medium size enzymes, such as proteases, lipases and peroxidases, via physisorption, encapsulation and tethering on the internal surfaces of the solids. Use has also been made of silicas functionalized for this purpose. In many cases the immobilized enzymes are both active and re-usable. Here we review the studies on enzymes immobilized on ordered mesoporous solids and assess the need for careful studies in real applications. Furthermore, we note the emerging applications of related biomolecule–mesoporous solid hybrids in other applications, such as intracellular drug delivery and transfection technology.

Enzyme immobilisation using siliceous mesoporous molecular sieves

Abstract The use of mesoporous molecular sieves in enzyme immobilisation has been studied. Three different types of mesoporous sieves (MCM-41, MCM-48 and SBA-15) were selected because of the differences in their pore dimensions and structures. Commercially available porous silica gel was chosen for comparison. The model enzyme chosen in this study was trypsin. The samples of immobilised trypsin were active for the hydrolysis of N-α-benzoyl- dl -arginine-4-nitroanilide (BAPNA). The amount of enzyme adsorbed on the supports was found to be related to the pore size of the molecular sieves. Moreover, the pore size and the structure of the support also affected the activity of the supported enzymes.

Size selective protein adsorption on thiol-functionalised SBA-15 mesoporous molecular sieve

The mesoporous silica SBA-15, functionalised with propylthiol groups during synthesis and rendered porous (mean pore diameter 51 A) by extraction of surfactant template molecules, shows strong and size selective adsorption of proteins, selectively excluding those with molecular weights of ca. 40000 u and above. A model for the adsorption process is proposed, in which reversible physisorption is followed by irreversible chemisorption. Adsorption of proteins on an unfunctionalised SBA-15 from which the template has been removed by calcination, (mean pore diameter 56 A) shows shape selective and reversible adsorption of proteins with molecular weights of ca. 43000 u and below.

Preparation and characterization of polyethylenimine-coated Fe3O4-MCM-48 nanocomposite particles as a novel agent for magnet-assisted transfection.

A new type of magnetic nanoparticle was synthesized using mesoporous silica MCM-48 as a template. Magnetite (Fe(3)O(4)) nanocrystals were incorporated onto the MCM-48 silica structure by thermal decomposition of iron(III) acetylacetonate. The particle size of these Fe(3)O(4)-MCM-48 composite particles is around 300 nm with an iron oxide content of ca. 20% w/w. Measurements from SQUID magnetometry suggest that these nanoparticles possess superparamagnetic properties similar to those of Fe(3)O(4) nanoparticles. By coating positively charged polyethylenimine on to the surface, DNA can be bound onto the Fe(3)O(4)-MCM-48 nanoparticles. Transfection studies showed that these PEI-Fe(3)O(4)-MCM-48 particles were highly effective as a transfection reagent, and a 400% increase of transfection efficiency compared with the commercial products was recorded.

Differences in magnetic particle uptake by CNS neuroglial subclasses: implications for neural tissue engineering

AIM To analyze magnetic particle uptake and intracellular processing by the four main non-neuronal subclasses of the CNS: oligodendrocyte precursor cells; oligodendrocytes; astrocytes; and microglia. MATERIALS & METHODS Magnetic particle uptake and processing were studied in rat oligodendrocyte precursor cells and oligodendrocytes using fluorescence and transmission electron microscopy, and the results collated with previous data from rat microglia and astrocyte studies. All cells were derived from primary mixed glial cultures. RESULTS Significant intercellular differences were observed between glial subtypes: microglia demonstrate the most rapid/extensive particle uptake, followed by astrocytes, with oligodendrocyte precursor cells and oligodendrocytes showing significantly lower uptake. Ultrastructural analyses suggest that magnetic particles are extensively degraded in microglia, but relatively stable in other cells. CONCLUSION Intercellular differences in particle uptake and handling exist between the major neuroglial subtypes. This has important implications for the utility of the magnetic particle platform for neurobiological applications including genetic modification, transplant cell labeling and biomolecule delivery to mixed CNS cell populations.

Multifunctional Fe3O4 nanoparticles for targeted bi-modal imaging of pancreatic cancer

Amine and carboxylic acid-bifunctionalized iron oxide nanoparticles with robust silane linkages to the nanoparticle surface were prepared with a versatile direct grafting protocol. The contrast in chemistry of these two groups was highlighted by attaching a fluorophore, Rhodamine B isothiocyanate (RITC) onto the amine group and an antibody (EPCAM – epithelial cell adhesion molecule) onto the carboxylic acid groups. The iron oxide core and the RITC tags provide the MRI-fluorescent bi-modal imaging capability. The EPCAM antibody is specific to a protein ubiquitously expressed on the epithelial cell surface. These bifunctionalized nanoparticles target and then undergo facilitated uptake into pancreatic cancer cells (Panc-1) in a time course-monitored controlled study. The integrated optical imaging properties of these magnetic nanoparticles were utilized to monitor the interaction of the nanoparticles with the EPCAM receptors on the cell membrane of the Panc-1 cells. The time-course of the uptake for the targeted and the control particles by the cells was followed allowing the localization within the cell and the impact of particle functionalization to be identified. This system is a candidate for further development as a multi-modular imaging, diagnostic and delivery tool.

A triple-layer design for polyethyleneimine-coated, nanostructured magnetic particles and their use in DNA binding and transfection

Nanostructured iron oxide–silica particles have been prepared using SBA-15 mesoporous silica particles as a template. Iron oxide nanoparticles were impregnated inside the mesopores of the silica particles via a wet impregnation method. The resultant material exhibited superparamagnetic properties with an unsaturated magnetic moment due to the formation of iron (III) oxide nanoparticles inside the mesopores. The surface of these iron oxide–silica particles has also been coated with polyethyleneimine (PEI) to enable attachment of DNA. The PEI-coated particles showed a high DNA binding capacity and have great potential for development as a new vehicle for gene delivery.

Lewis and Brønsted acid catalysis with AlMCM-41 and AlMMS: dependence on exchange cation

Mesoporous solid acid catalysts based on AlMCM-41 and AlMMS have been prepared. The two catalysts exhibit similar unidimensional pore structures with hexagonal symmetries. AlMMS shows less long-range order than AlMCM-41 but is considerably easier to synthesise. The catalytic activities have been measured and compared in the Lewis-acid-catalysed alkylation of toluene with benzyl chloride, and the Brønsted-acid-catalysed alkylation of toluene with benzyl alcohol. Activities have been measured for catalysts ion-exchanged with H+, Fe3+, Al3+ and Na+, and following thermal activation at temperatures of 150–350°C. They have also been compared with K10, a mesoporous acid-treated clay catalyst. Results show that the acid-treated clay is the most active of the three catalysts in both reactions. For all catalysts, the Fe3+ forms exhibit the highest Lewis acid catalytic activities, and the Al3+ and H+ forms show higher Brønsted acid activities. Infrared spectra of adsorbed pyridine show relative concentrations of Lewis and Brønsted acid sites consistent with this. Differences in the dependence of catalytic activities on thermal activation temperature are interpreted in terms of the hydration properties of the catalysts.

Chemical Grafting of a DNA Intercalator Probe onto Functional Iron Oxide Nanoparticles: A Physicochemical Study

Spherical magnetite nanoparticles (MNPs, ∼ 24 nm in diameter) were sequentially functionalized with trimethoxysilylpropyldiethylenetriamine (TMSPDT) and a synthetic DNA intercalator, namely, 9-chloro-4H-pyrido[4,3,2-kl]acridin-4-one (PyAcr), in order to promote DNA interaction. The designed synthetic pathway allowed control of the chemical grafting efficiency to access MNPs either partially or fully functionalized with the intercalator moiety. The newly prepared nanomaterials were characterized by a range of physicochemical techniques: FTIR, TEM, PXRD, and TGA. The data were consistent with a full surface coverage by immobilized silylpropyldiethylenetriamine (SPDT) molecules, which corresponds to ∼22,300 SPDT molecules per MNP and a subsequent (4740-2940) PyAcr after the chemical grafting step (i.e., ∼ 2.4 PyAcr/nm(2)). A greater amount of PyAcr (30,600) was immobilized by the alternative strategy of binding a fully prefunctionalized shell to the MNPs with up to 16.1 PyAcr/nm(2). We found that the extent of PyAcr functionalization strongly affects the resulting properties and, particularly, the colloidal stability as well as the surface charge estimated by ζ-potential measurement. The intercalator grafting generates a negative charge contribution which counterbalances the positive charge of the single SPDT shell. The DNA binding capability was measured by titration assay and increases from 15 to 21.5 μg of DNA per mg of MNPs after PyAcr grafting (14-20% yield) but then drops to only ∼2 μg for the fully functionalized MNPs. This highlights that even if the size of the MNPs is obviously a determining factor to promote surface DNA interaction, it is not the only limiting parameter, as the mode of binding and the interfacial charge density are essential to improve loading capability.