BackgroundThe blood brain barrier (BBB) controls the brain microenvironment and limits penetration of the central nervous system (CNS) by chemicals, thus creating an obstacle to many medical imaging and treatment procedures. Research efforts to identify viable routes of BBB penetration have focused on structures such as micelles, polymeric nanoparticles and liposomes as drug carriers, however, many of them failed to provide unequivocal proof of BBB penetration. Here we proved that gold nanoparticles (AuNPs) penetrate the BBB in rats to reach brain regions.ResultsInjection of AuNPs to the abdominal cavity of rats resulted in levels of gold found in blood, urine, brain regions and body organs. After perfusion the concentration of gold in brain regions diminished dramatically indicating that most of the gold was in venous blood and not in the brain tissues. Injection of Na, K or Ca ion channel blockers reduced BBB penetration by half. A biological half-life of 12.9 ± 4.9 h was found for the gold nanoparticles. Possible mechanisms for the transport of AuNPs through the BBB are discussed.ConclusionsBBB penetration by AuNPs is spontaneous without the application of an external field. A major amount of gold resides in blood vessels therefore perfusion required. Ion channel blockers can be used to control the transport of AuNPs.Electronic supplementary materialThe online version of this article (doi:10.1186/s12951-015-0133-1) contains supplementary material, which is available to authorized users.

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The isotopic ratio (234)U/(238)U in drinking water and in hair, toenail, and urine samples from 45 individuals who consumed 0.2-2775 microg d(-1) of uranium in their drinking water was determined using a multi-collector inductively coupled plasma mass spectrometer (MC-ICPMS). The U/U atom ratio in the water samples varied from 51 x 10(-6) to 252 x 10(-6) whereas in secular equilibrium (i.e., unity activity ratio) the ratio is 54.9 x 10(-6). The correlation of the (234)U/(238)U ratio between hair and nail samples was 0.98, and between hair and nails and urine the ratio was 0.91 and 0.89, respectively. The correlation of the ratio between water and the hair or nails was 0.97 but only 0.72 for water and urine, possibly due to spectral interferences. These results conclusively demonstrated that the uranium found in the bioassays can be traced to the drinking water, thus providing a direct link to the source of exposure. Hair may serve as an excellent indicator of occupational or environmental exposure to uranium and provide information regarding its source. Bioassay of hair is attractive as it is an effective bio-concentrator, samples can be easily stored, the concentration reflects an integrated value, and, finally, the measurement of the (234)U/(238)U isotopic ratio in digested hair samples by MC-ICPMS is feasible and highly informative. Hair bioassay can also be used to assess exposure to depleted uranium long after the subjects have left the area suspected of contamination.