Magnetic single-enzyme nanoparticles with high activity and stability

Magnetic single-enzyme nanoparticles (SENs) encapsulated within a composite inorganic/organic polymer network were fabricated via the surface modification and in situ aqueous polymerization of separate enzyme molecule. The resultant nanoparticles were characterized by transmission electron microscope (TEM), Fourier transform infrared (FTIR) spectrometer and X-ray diffraction (XRD). These particles are almost spherical in shape and have a unique size of about 50 nm in diameter. Electrical and magnetic measurements reveal that the magnetic SENs have a conductivity of 2.7 x 10(-3) S cm(-1), and are superparamagnetic with a saturation magnetization of 14.5 emu g(-1) and a coercive force of 60 Oe. Compared with free enzyme, encapsulated enzyme exhibits a strong tolerance to the variation of solution pH, high temperature, organic solvent and long-term storage, thus showing significantly enhanced enzyme performance and stability. (C) 2007 Published by Elsevier Inc.