Magnetic and structural properties of a DNA-maghemite nanocomposite

Starting with 7 nm γ Fe2 O3 nanoparticles, synthesis of DNA- γ Fe2 O3 nanocomposite and its structural/magnetic properties vis-a-vis the parent γ Fe2 O3 are reported. Analysis of the x-ray diffraction shows an increase in the particle strain and average particle size (to 9.7 nm) in DNA- γ Fe2 O3 nanocomposite. Transmission electron microscopy also shows an increase in size and a considerably wider size distribution. Temperature (5-300 K) variation of the magnetization (M) shows a wider distribution of the blocking temperatures (TB), as expected from the wider size distribution. Above TB, the data of M vs H fit the modified Langevin function with magnetic moment/particle μp ≈11 000 μB, somewhat larger than μp ≈8000 μB for the parent γ Fe2 O3. However, Mg (γ Fe2 O3) is not significantly affected. In electron magnetic-resonance spectroscopy at 9.28 GHz, only a single line is observed in DNA- γ Fe2 O3 nanocomposite compared to two lines in γ Fe2 O3. These effects are discussed in terms of the above structural differences.