Introduction:
Though widely studied for biomedical applications, the lack of current systemic studies on the in vivo fate of single-walled carbon nanohorns (SWCNHs) largely restricts their further applications, as real-time monitoring of their biodistribution remains a big challenge. Here, we aim to customize a label-free multispectral optoacoustic tomography (MSOT) method and systematically survey the fate of oxidized SWCNHs (SWCNHox) following different exposure routes by whole body imaging.

Methods:
Mice were given a suspension of SWCNHox with an average size of 136.4 nm via four different administration routes, and then imaged by MSOT.

Results:
After oral gavage, SWCNHox were mainly distributed in the gastrointestinal tract then excreted through the gut. Compared with the observation post first dosing, the accumulation of SWCNHox in the gastrointestinal tract was not obvious even after four-time oral gavage. Almost no SWCNHox were found at detectable levels in kidney, liver, blood and spleen. Following intravenous (iv) injection, SWCNHox were mainly presented and persisted in the spleen and liver, while very little in the kidney and almost none detectable in the intestine. SWCNHox accumulated significantly in the liver and spleen after four IV administrations. Following hypodermic and intramuscular injections, almost no SWCNHox could cross biological barriers and transport to the spleen, kidney or liver, likely due to their very low absorption rate. Almost all SWCNHox remained around the injection sites. For the first time, we have systematically investigated the in vivo fate of SWCNHs in a label-free and real-time manner.

Conclusion:
The findings of this study provide insights into the selection of appropriate exposure routes for potential biomedical applications of carbon nanomaterials.

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