Carboxymethylation of dextran for surface modification of magnetite nanoparticles

Magnetite nanoparticles are currently studied for biomedical applications such as MRI, drug delivery, and magnetic fluid hyperthermia (MHF). These applications require nanoparticles with a suitable coating which provides colloidal stability and improves the nanoparticle's transport and interaction with biological tissues. Polysaccharides such as dextran have been used for this purpose due to their biocompatibility, low toxicity, and versatility for nanoparticle suspension in cell culture media. Functionalization of magnetite nanoparticles with dextran was performed by carbodiimide chemistry in which amine groups previously grafted onto the nanoparticle's surface are reacted with carboxylic groups (--COOH) present in the dextran chain. These --COOH groups were introduced in the dextran chains by a carboxymethylation reaction, obtaining a carboxymethyl-dextran molecule (CMDx). The amount of --COOH groups per chain was controlled by different parameters such as reaction time, temperature, and sodium hydroxide and monochloroacetic acid (ClCH2COOH) concentrations. CMDx with different degrees of substitution were prepared and the nanoparticle's surface charge and stability were studied using zeta potential measurements and dynamic light scattering. Results showed that decreasing the number of --COOH groups per dextran chain decrease the nanoparticle's surface charge without affecting their colloidal stability. The nanoparticles coated with CMDx with 5, 23 and 38 --COOH groups per dextran chain were stable over the entire range of pH and NaCl concentration studied.