Mouse Positron Emission Tomography Study of the Biodistribution of Gold Nanoparticles with Different Surface Coatings Using Embedded Copper-64.

By taking advantage of the ability of 64Cu to bind nonspecifically to gold surfaces, we have developed a methodology to embed this radionuclide inside gold nanoparticles (AuNPs). 64Cu enables the in vivo imaging of AuNPs by positron emission tomography (PET). AuNPs have a multitude of uses within health technology and are useful tools for general nanoparticle research. 64Cu-AuNPs were prepared by incubating AuNP seeds with 64Cu2+, followed by the entrapment of the radionuclide by grafting on a second layer of gold. This resulted in radiolabeling efficiencies of 53 ± 6%. The radiolabel showed excellent stability when incubated with EDTA for 2 days (95% radioactivity retention) and showed no loss of 64Cu when incubated with 50% mouse serum for 2 days. The methodology was chelator-free, removing traditional concerns over chelator instability and altered AuNP properties due to surface modification. Radiolabeled 64Cu-AuNP cores were prepared in biomedically relevant sizes of 20-30 nm and used to investigate the in vivo stability of three different AuNP coatings by PET imaging in a murine xenograft tumor model. We found the longest plasma half-life (T1/2 about 9 h) and tumor accumulation (3.9%ID/g) to result from a polyethylene glycol coating, while faster elimination from the bloodstream was observed with both a Tween 20-stabilized coating and a zwitterionic coating based on a mixture of sulfonic acids and quaternary amines. In the in vivo model, the 64Cu was observed to closely follow the AuNPs for each coating, again attributed to the excellent stability of the radiolabel.