Nanobody-modified gold nanoparticles were used to explore their ability to achieve selective targeting in vitro and in vivo to distinct cell type(s), based on the specificity of the nanobody that was installed. We developed conjugation methods that exploit click chemistry for octahedral ∼50 nm gold nanoparticles and chiral ∼180 nm gold nanoparticles. We determined that each of these particles could be modified with ∼75 and ∼330 nanobodies, respectively. Particle-bound nanobodies retain their antigen binding capacity. After conjugation of the mouse Class II MHC-specific nanobody VHH7 to chiral gold nanoparticles, selective targeting of Class II MHC-positive cell types was observed in vitro by fluorometric assays and by dark-field microscopy. Upon installation of the positron emission tomography (PET) isotopes 89Zr or 64Cu on nanobody-modified gold nanoparticles and retro-orbital injection of the radiolabeled particles, we observed accumulation predominantly in the liver and to a far lesser extent in the spleen, regardless of the size of the gold nanoparticles and the identity of the attached nanobody. We observed a striking difference in the distribution of radioisotope-labeled gold nanoparticles by changing the route of administration to intraperitoneal delivery. Significantly reduced accumulation in the liver and spleen was observed by intraperitoneal injection of nanoparticles. In the case of nanobody-modified gold nanoparticles injected intraperitoneally, prominent and persistent signals from the parathymic lymph nodes were observed in the PET/computed tomography images.
Keywords: PET imaging; click reaction; gold nanoparticles; nanobody; radioisotope labeling.