In the present work, magnetic separation was performed on a high-gradient magnetic separator, and the processing composite nanoparticles are well-dispersed in aqueous solution. Other authors had characterized Au-Fe composite nanoparticles by magnetic separation approach. Thus, the existence of magnetic core/cores inside particles of Au character can be confirmed, provided the magnetically collected particles exhibit the characteristic red color of Au colloid in liquid media.
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Note that in pure Au nanoparticles, the collective oscillations of free electrons, known as the surface plasmon (SP), cause an absorption peak to appear in the visible region of the electromagnetic spectrum, whereas Fe oxide particles have no specific absorption peak in this region. For this reason, evidence complementary to that of energy dispersive spectroscopy (EDS) is needed for characterizing composite nanoparticles of this kind.
In general, TEM images cannot show the core–shell structure of these nanoparticles, since the electronic density of Au is much higher than that of Fe oxide. Herein, we report on the preparation of such nanoparticles by the citrate reduction of Au 3+ in the presence of heterogeneous seeds. Water-soluble, Au-coated magnetic Fe oxide nanoparticles were synthesized recently by the reduction of Au 3+ onto the surfaces of magnetic seeds via iterative hydroxylamine seeding. , gold nanoparticles can be homogeneously grown to larger ones via seeding approach, either using sodium citrate or hydroxylamine as a reducing agent. But to maximize the tunability of chemical functionality and, ultimately, biomedical applicability, an aqueous-based synthesis route is more favorable, since these applications require magnetic nanoparticles to be well-dispersed in liquid media. Similar magnetic core/shell structured or dumbbell-like particles of Au–Fe composition have been synthesized in microemulsions. Coating them with a gold shell, to which the coupling and functionalization with biological components has been established, will offer more opportunities toward using magnetic nanoparticles for biomedical purposes.
As it is well-known, superparamagnetic iron oxide nanoparticles (SPION) provide attractive possibilities in biomedical applications, such as cell labeling and separation, , magnetic resonance imaging (MRI), ,, target drug delivery and magnetic ferrofluids hyperthermia (MFH),.
The magnetic core/gold shell nanoparticle, for example, is one of such nanocomposites. Interests in this kind of nanomaterials originate not only from the curiosities of scientists who are exploring the mesoscopic world, but also from the ever-increasing demands placed on materials synthesis and performance by nanotechnology. As an emerging active area of contemporary materials science, nanocomposites containing two or more different nanoscale functionalities attract much attention, ,,.