A Simple Approach to the Design and Functionalization of Fe 3 O 4 –Au Nanoparticles for Biomedical Applications

Chitosan‐stabilized Fe 3 O 4 nanoparticles (Fe 3 O 4 –CHI NPs) are synthesized at room temperature in an aqueous medium and gold NPs are decorated on the surface of these nanoparticles by the deposition/precipitation method. The synthesis of Fe 3 O 4 /Au NPs is followed by biofunctionalization with lipoic acid and thereafter the carboxy terminated groups of the Fe 3 O 4 /Au–lipoic acid composite NPs are coupled to multidentate iminodiacetic acid (IDA) by adopting (1‐ethyl‐3‐(3‐dimethylamino propyl) carbodiimide and N ‐hydroxysulfosuccinimide chemistry. These Fe 3 O 4 /Au–LA–IDA particles are finally allowed to complex with Cu 2+ ions resulting in a net positive surface charge. Detailed physicochemical properties of the synthesized NPs have been carried out by XRD, TEM, FT‐IR, XPS, TOC, AAS, TG‐DTA, and zeta‐potential measurements. The super paramagnetic response is investigated by vibrating sample magnetometry and feasibility of these materials as an efficient MRI contrast agent ( r 2 =(124.3±13.6) m M −1 s −1 ) have been also demonstrated in a phosphate‐buffered saline suspension. Finally, the Fe 3 O 4 /Au–LA–IDA–Cu 2+ composite NPs are used as an immobilized metal affinity matrix to separate expressed His6‐tagged protein (>95 % purity) from bacterial lysates and also from a large excess of bovine serum albumin to demonstrate the convenience of using this matrix for rapid purification of heterologously expressed proteins from biological mixtures.