Thiolated Gd(III) chelate coated gold nanoparticles: Synthesis, characterization, x-ray CT and MRI relaxivity studies

Gadolinium complex of 2-aminothiophenol conjugated DTPA (DTPA=diethylenetriamine N,N,N',N",N" -pentacetic acid) bis(amide) has been synthesized and characterized by various analytical techniques such as elemental analysis (EA), NMR, FAB-MS, IR, UV etc. This thiolated GdL (where L is a conjugate of DTPA and 2-aminothiophenol) has been anchored on the gold nanoparticles surfaces through thiols functionalites. These gold nanoparticles (AuNPs) have been synthesized by the reduction of gold tetrachloride (HAuCl₄) using sodium citrate as reducing agent. The surface functionalization has been performed by the replacement of citrate coat on the gold nanoparticle surface with thiolated Gd-chelate, Au@GdL. The Au@GdL has been analyzed by XRD, transmission electron microscope (HRTEM), UV, ICP-MS etc. The average size of nanoparticles is about 22 nm with a uniform spherical shape. A very high number of GdL has been loaded on nanoparticle surface reaching up to 7.9x103 of Gd(III)- chelates per nanoparticle and they demonstrate very high r₁ relaxivity and the r₁ relaxivity per [Gd] is much higher than the Gd(III)- chelate alone. The bimodality has also been tested using in-vitro x-ray computed tomography (x-ray CT). These nanoparticles (GNP's) are very stable and homogeneously dispersed in aqueous solution.