Gold nanoparticles

X-Ray imaging (computed tomography, CT) visualizes tissue density differences that provide the image contrast produced by X-ray attenuation between electron-dense bone and soft tissues (1). Contrast enhancement with use of X-ray contrast (radiopaque) agents are needed to increase the degree of contrast between diseased tissues from normal tissues. Water-soluble X-ray contrast agents are generally based on small tri-iodobenzene compounds as monomers or dimmers (2), which can be ionic (high osmolality) or nonionic (low osmolality). When injected intravenously (intra-arterial catheterization is commonly used), they exhibit highly non-specific vascular permeation and rapid renal excretion limiting their targeting performance. Gold has not been used as an X-ray contrast agent . Gold has a higher atomic number and a higher absorption coefficient than iodine, providing 2.7-fold greater contrast/weight than iodine (3). Furthermore, imaging gold at 80-100 keV reduces interference from bone absorption and provides lower soft tissue absorption, which would reduce radiation to patient. Hainfeld et al. (3) have performed experiments in mice using gold nanoparticles (AuNPs, 1.9 nm in diameter, ~50 kDa) as a CT contrast agent. This preparation exhibit excellent stability, high X-ray absorption, good safety profile, long blood half-life, and enhanced CT contrast of the vasculature, kidneys and tumor in mice.