Masahiro Muraoka

Ferritin as a bionano-particulate emulsifier

Stable Pickering-type emulsions were prepared using ferritin, a spherical protein, as a bionano-particulate emulsifier and n-dodecane, toluene, castor oil, olive oil or vegetable oil as an oil phase, in the absence of any surfactant molecules. All the emulsions prepared were of the oil-in-water type and an increase of ferritin concentration decreased the volume average droplet diameters. Transmission electron microscopy studies of the ferritin residues remaining after evaporation of oil and water from the emulsion revealed a broken capsule morphology, which is strong evidence for the attachment of ferritin at the oil-water interface thereby stabilizing the emulsion. The emulsion droplets could be elongated and made to pass through a glass capillary.

Electrostatic adsorption of ferritin, proteins and nanoparticle conjugate onto the surface of polyelectrolyte multilayers

In this study, we quantitatively and kinetically analyzed the electrostatic adsorption of ferritin and apoferritin onto the surface of precursor films by using QCM, SEM and AFM. The precursor films were successively prepared by the alternate adsorption of poly(diallyldimethylammonium chloride) (PDDA) and poly(sodium 4-styrenesulfonate) (PSS) in the presence of suitable NaCl concentrations onto the QCM substrate. We observed their formation processes by frequency shifts of QCM. Furthermore, we also observed the adsorption of (apo)ferritin by an electrostatic interaction onto the outermost layer surface by QCM. The adsorption behavior of (apo)ferritin revealed the specific adsorption that (apo)ferritin only recognizes the surface of a precursor film depending on its surface charges in order to adsorb onto it. We also studied the effects of (apo)ferritin solution concentration, pH and washing/drying process on their adsorption behavior. This study on the immobilization of protein supramolecules will provide a method to build more complex functional inorganic nanostructures.

Characterization of stable, electroactive protein cage/synthetic polymer multilayer thin films prepared by layer-by-layer assembly

We have fabricated electroactive multilayer thin films containing ferritin protein cages. The multilayer thin films were prepared on a solid substrate by the alternate electrostatic adsorption of (apo)ferritin and poly(N-isopropylacrylamide-co-2-carboxyisopropylacrylamide) (NIPAAm-co-CIPAAm) in pH 3.5 acetate buffer solution. The assembly process was monitored using a quartz crystal microbalance. The (apo)ferritin/poly(NIPAAm-co-CIPAAm) multilayer thin films were then cross-linked using a water-soluble carbodiimide, 1-[3-(dimethylamino)propyl]-3-ethylcarbodiimide. The cross-linked films were stable under a variety of conditions. The surface morphology and thickness of the multilayer thin films were characterized by atomic force microscopy, and the ferritin iron cores were observed by scanning electron microscopy to confirm the assembly mechanism. Cyclic voltammetry measurements showed different electrochemical properties for the cross-linked ferritin and apoferritin multilayer thin films, and the effect of stability of the multilayer film on its electrochemical properties was also examined. Our method for constructing multilayer films containing protein cages is expected to be useful in building more complex functional inorganic nanostructures.

Precise control of two-dimensional composition of proteins and nanoparticle conjugate for functional nanostructured material fabrication.

In this study, we quantitatively analyzed the electrostatic blend adsorption of ferritin and apoferritin onto the surface of the precursor films by using a quartz crystal microbalance (QCM), X-ray photoelectron spectroscopy (XPS), and scanning electron microscopy (SEM). The precursor films were successively prepared by the alternate adsorption of poly(diallyldimethylammonium chloride) (PDDA) and poly(sodium 4-styrenesulfonate) (PSS) in the presence of 150 mM NaCl concentration onto the QCM substrate. We observed a monolayer adsorption of both ferritin and apoferritin by means of electrostatic interaction onto the outermost PDDA surface at pH 10.0. Under this condition, the composition of ferritin and apoferritin within the monolayer is linearly dependent on their ratios in the blended solution, thus showed an ideal blend adsorption behavior. The perfectly identical structure of ferritin and apoferritin should be contributed to this ideal blend adsorption behavior. We also studied the effects of total concentrations of their solution on ferritin and apoferritin blend adsorption. This study on the blend adsorption of ferritin and apoferritin by electrostatic interaction will be applied to the fabrication of multi-components homogeneous NP array because apoferritin can accommodate a variety of nanometer size inorganic materials within their interior spaces.

Formation of a pseudorotaxane, capable of sensing cations via dethreading molecular motion, from a cryptand and bipyridinium salts

A new type of cryptand-based pseudorotaxane was prepared, utilizing a novel cryptand incorporating two aromatic rings as a wheel component, combined with various bipyridinium salts as the axle component. These pseudorotaxanes exhibited charge-transfer absorption at approximately 380xa0nm due to π-electron interactions between the cryptand and the bipyridinium salt. Upon addition of one equivalent of sodium ion to the pseudorotaxane, this absorption was observed to disappear as a result of displacement of the bipyridinium salt by the sodium.