Natural nanotube-based biomimetic porous microspheres for significantly enhanced biomolecule immobilization

Inorganic nanostructures and their assemblies play important roles in immobilizing biomolecules. Herein, we developed a facile and green methodology to assemble natural halloysite nanotubes (1D building blocks) into nest-like porous microspheres (3D architecture). We further modified the microspheres with dopamine to form a biomimetic entity. The interconnected and hierarchical pores within the microspheres provide larger pore volume to entrap biomolecules, and the abundant functional groups on the pore surface bond covalently with enzyme to enhance the immobilization ability. The porous microspheres showed excellent loading capacity for laccase immobilization as high as 311.2 mg/g, around 30 times higher than the individual halloysite nanotubes (11.3 mg/g). The specific activity above 80% was retained for the immobilized laccase compared to the free laccase. In addition, the immobilized enzyme exhibited remarkable thermal and recycle use stability. The biomimetic microspheres are expected to be biologically safe and chemically stable microcapsules for immobilizing a variety of biomolecules because of their natural and biofriendly characteristics. © 2013 American Chemical Society

Adsorption of Dopamine on Rutile TiO2(110): A Photoemission and Near-Edge X-ray Absorption Fine Structure Study

Synchrotron radiation photoelectron spectroscopy and near-edge X-ray absorption fine structure (NEXAFS) techniques have been used to study the adsorption of dopamine on a rutile TiO2 (110) single crystal. Photoemission results suggest that dopamine bonds through the oxygen molecules in a bidentate fashion. From the data, it is ambiguous whether the oxygens bond to the same 5-fold coordinated surface titanium atom or bridges across two, although based on the bonding of pyrocatechol on rutile TiO2 (110), it is likely that the dopamine bridges two titanium atoms. Using the searchlight effect, the carbon K-edge near-edge X-ray absorption fine structure NEXAFS spectra recorded for dopamine on rutile TiO2 (110) show the phenyl ring to be oriented at 78° ± 5° from the surface and twisted 11 ± 10° relative to the (001) direction