Preparation and properties of superparamagnetic nanoparticles with narrow size distribution and biocompatible

A chemical co-precipitation method capable of controlling the average size and size distribution of magnetic Fe₃O₄ nano-particles was developed. It was found that the homogeneous variation of the pH value in the solution plays a role in the size distribution of the synthesized Fe ₃O₄ particles. In this work, we added urea to the ferrite solution, followed by heating the solution to decompose the urea before titrating a base solution into the ferrite solution. Thus, the variation in pH value in the solution can become uniform, and the uniformity in the particles size can be greatly enhanced. In addition, the average particle size is adjustable via control of the amount of urea decomposing at one time. To be biocompatible, dextran is selected as the surfactant for the Fe ₃O₄ particles, because of its non-toxicity and high bio-affinity. The desired bio-probes can be coated on the dextran layer through adequate chemical reactions.