Abstract

On account of the biological compatibility of magnetic nanoparticle, it is especially
common to use carbohydrates or polysaccharides as the coating materials. The dextran is the
most commonly used surfactant now because it contains no toxicity, has a longer in vivo
circulation and different molecular weight. This research aims at coating the magnetic
nano-particles with dextrans by the one-step preparation method, which is newly developed
by our laboratory, and tries to discuss its effect on the value of SAR through an inspection on
its synthesis condition, the size of the particle which is covered with dextran, and the coating
dextrans with different molecular weights.
Based on the experimental results, it may be concluded: First of all, we can use magnetic
decantation as a way to accelerate magnetic nanoparticles in subsidence and to separate out
the overdose of organic solvent on the surface layer. Then, we pour overdose of deionized
water into it, and, for several times, separate out the materials which has reach the level of
purified sample. However, the magnetic nanoparticles, which has gone through one-step
conjugation process with the use of dextran, can be well mixed in deionized water, and cannot
cleanse the overdose of organic materials and salt in aqueous with the use of magnetic
subsidence or centrifugal process. Second, one-step preparation method can conjugate the
shell and core of nanoparticle at the same time. The shell is dextran, and the core is magnetic
nanoparticle. It will be more efficient and time-saving in conjugation. Third, the complexes in
this study were examined by SEM photograpy to insure the qualities , it has a narrower
distribution of nanoparticle size. The qualification of particle appears to be better than others
in the literatures . In one-step conjugation process, because Fe3+ forms Fe-O-Fe bridge in
water, we make dextran capture Fe3+, and then, add Fe2+ inside and it subsides with base
solution together. As a result, it can quickly form the shell and core of magnetic nanoparticle
and limit the growth of size of nanoparticle. Fourth, one-step preparation method has a smaller
value of SAR, each of the different molecular weight are 48.1±7.3 W/g (MW=9,000-11,000)
and 24.6±5.7 W/g (MW=64,000-76,000) respectively. The value of SAR is lower than that has
been provided by the literatures, and there is a way called two-steps method to improve this
situation, to prepare magnetic nanoparticles in advance. Comparing with the one-step
preparation method, the two-steps method can form a more completed crystal, and this will
have an better effect on the characteristic of the SAR. The element Boron coming from
NaBH4 was not also found in EDS analysis.