We have developed novel
gold-
silver alloy nanoshells as magnetic resonance imaging (MRI) dual T1 (positive) and T2 (negative)
contrast agents as an alternative to typical
gadolinium (Gd)-based
contrast agents. Specifically, we have doped iron oxide nanoparticles with Gd
ions and sequestered the
ions within the core by coating the nanoparticles with an
alloy of
gold and
silver. Thus, these nanoparticles are very innovative and have the potential to overcome toxicities related to renal clearance of
contrast agents such as
nephrogenic systemic fibrosis. The morphology of the attained nanoparticles was characterized by XRD which demonstrated the successful incorporation of Gd(III)
ions into the structure of the
magnetite, with no major alterations of the
spinel structure, as well as the growth of the
gold-
silver alloy shells. This was supported by TEM, ICP-AES, and SEM/EDS data. The nanoshells showed a saturation magnetization of 38 emu/g because of the presence of Gd
ions within the crystalline structure with r1 and r2 values of 0.0119 and 0.9229 mL mg-1 s-1, respectively (Au:Ag
alloy = 1:1). T1- and T2-weighted images of the nanoshells showed that these agents can both increase the surrounding water
proton signals in the T1-weighted image and reduce the signal in T2-weighted images. The as-synthesized nanoparticles exhibited strong absorption in the range of 600-800 nm, their optical properties being strongly dependent upon the thickness of the
gold-
silver alloy shell. Thus, these nanoshells have the potential to be utilized for
tumor cell ablation because of their absorption as well as an imaging agent.