Functionalization of magnetic nanoparticles with organic molecules: loading level determination and evaluation of linker length effect on immobilization.

A general method is introduced to immobilize organic molecules on magnetic nanoparticles through silanization reactions and determine the maximum loading level by UV-vis spectroscopy. Loading levels of 1.5 x 10(-3) mol per gram of nanoparticle were obtained with structurally diverse compounds such as rhodamine B and glucosamine. The length of the linker did not have a significant effect on loading as comparable maximum amounts of rhodamine B were immobilized on magnetic nanoparticles regardless of the linker length. Interestingly, rhodamine B derivatives lost conjugation during synthetic manipulations due to reversible spiroisobenzofuran formation. Full regeneration of conjugation was found to be slow with rhodamine B attached on magnetic nanoparticles. The results obtained from these studies will be useful for studying surface functionalization of MNPs in general. (c) 2007 Wiley-Liss, Inc.