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a b s t r a c tSuccessful application of gold nanoparticles (AuNPs) in biomedicine requires extensive safety assessment for which biokinetic studies are crucial.We evaluated the biodistribution of AuNPs ($20 nm) with different surface coatings: citrate, 11-MUA and 3 pentapeptides, CALNN, CALND and CALNS, after i.v. administration to rats (0.6-1 mg Au/kg). Biodistribution was evaluated based on Au tissue content measured by GFAAS.Citrate-AuNPs were rapidly removed from circulation with 60% of the injected dose depositing in the liver. Thirty minutes post-injection, the lungs presented about 6% of the injected dose with levels decreasing to 0.7% at 24 h. Gold levels in the spleen were of 2.6%. After 24 h, liver presented the highest Au level, followed by spleen and blood.A similar biodistribution profile was observed for MUA-coated AuNPs compared to Cit-AuNPs at 24 h post-injection, while significantly higher levels of peptide-capped AuNPs were found in the liver (74-86%) accompanied by a corresponding decrease in blood levels.TEM analysis of liver slices showed AuNPs in Kupffer cells and hepatocytes, trapped inside endosomes. Our data demonstrate that AuNPs are rapidly distributed and that the liver is the preferential accumulation organ. Peptide capping significantly increased hepatic uptake, showing the influence of AuNPs functionalization in biodistribution.