Synthesis of Bioconjugated Magnetic Nanoparticles for Magneto-Raman Study

Guangjun Cheng, Danilo Romero, David Dunmire, Angela Hight Walker
Physics Laboratory, National Institute of Standards and Technology (NIST), Gaithersburg, MD, USA

We are investigating the effects of an externally applied magnetic field on the structure and magnetic properties of biomolecules (DNA and proteins). A newly constructed, magneto-Raman confocal microscope system couples a cryo-magnet to a triple grating spectrometer enabling the measurements of Raman scattering over a wide range of temperatures (4.2K to 300K) and magnetic field strengths (0T to 8T). Two synthetic strategies have been used to provide bioconjugated magnetic nanoparticles for study with this instrument.

The first strategy takes advantage of biomimetic synthesis. Apoferritin, a demetalated protein, can be used to prepare ferritins with ferrihydirte cores by feeding Fe(II) ions to the protein solution. The antiferromagentic ferrtins with ferrihydrite cores can be converted into magnetic ferritins (magneto-ferritins) by chemical reconstitution of the ferrihydrite cores with the ferromagnetic magnetite. Three different cores in three different ferritins, apoferritins, antiferromagentic ferritins and magneto-ferritins provide ideal samples for magneto-Raman study.

The second strategy applies the modification of pre-synthesized magnetic nanoparticles. Magnetic nanoparticles (Co, Ni, Fe) with a wide size range from 3nm to 20 nm can be synthesized by thermodecomposition, and then Au shells can be grown on these pre-synthesized magnetic nanoparticles. The magnetic-core-Au-shell nanoparticles can improve their biocompatibility and enhance the Raman scattering while maintaining their unique magnetic properties. DNA or protein can be assembled on these modified nanoparticles for study.

Guangjun Cheng

phone: (301) 975-5209

fax: (301) 869-5700

Optical Technology Division (844), Physics Laboratory (PL)

Physics Building (221), Room B354

100 Bureau Drive, Stop 8441

Gaithersburg, MD 20899-8441