Albumin was conjugated to 16 nm gold particles (Alb-Au16) and infused into anesthetized pigs to determine if plasma, tissue and bronchoalveolar lavage (BAL) fluid concentrations of gold could be quantitated by neutron activation (Au198). Additionally, transmission electron microscopy (TEM) of lung and liver samples was evaluated for sites of gold distribution and morphological changes. The minimum concentration of gold detected by neutron activation ranged between 1.4 and 1.9 ppb (ng/gm of sample). No gold was detected in the plasma of pigs prior to Alb-Au16 infusion, while mean post infusion concentrations were 1.037 ± 0.69 ppm (μg/gm plasma, ±SD). The concentrations in the lung and liver were 274.4 ± 0.03 and 88.3 ± 0.04 ppm, respectively. There was no measurable Alb-Au16 in the BAL fluid. TEM showed gold particles within phagolysosomes in pulmonary and hepatic intravascular macrophages. No morphological changes were observed within the two populations of macrophages and no gold particles were observed within the alveolar space. Neutron activation of blood, tissue and BAL fluid samples from pigs administered intravenous Alb-Au16 was sensitive to the ppb concentration. The capability of neutron activation to detect very low concentrations of Au 198, combined with the freedom from contamination, make neutron activation an excellent technique for the study of the distribution and metabolism of a substance in vivo
