So from a brief look at the paper [0], the molecular submarine is just over 1,000g/mol For reference the haemoglobin A protein unit is about 64,000g/mol [1]. M

So from a brief look at the paper [0], the molecular submarine is just over 1,000g/mol For reference the haemoglobin A protein unit is about 64,000g/mol [1]. Molecules above about 500g/mol struggle to pass through the blood brain barrier [2] So ignoring everything else, this is a molecule that is considerably smaller than a cell but bigger than many pharmaceutical drugs. That's not to say anything more than 500g/mol is useless - metal-based or protein based molecules can rapidly jump up in size/weight but will usually travel through the body via alternative mechanisms to diffusion. [0] http://pubs.acs.org/doi/10.1021/acs.nanolett.5b03764 http://pubs.acs.org/doi/10.1021/acs.nanolett.5b03764 [1] https://en.m.wikipedia.org/wiki/Hemoglobin https://en.m.wikipedia.org/wiki/Hemoglobin [2] http://www.ncbi.nlm.nih.gov/pmc/articles/PMC539316/ http://www.ncbi.nlm.nih.gov/pmc/articles/PMC539316/