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I have a scenario where a person has nanorobots unknowingly injected into his bloodstream. I'd like his doctor to discover them through some kind of medical test, preferably a blood test. Of course they wouldn't be looked for specifically, but would have to show up as some kind of anomaly that would be investigated further, leading to their discovery. The type of test could either be a routine blood test that would be done on a person getting a general physical, or could be a blood test for a specific chronic condition (e.g. the person may have a medical condition requiring a specific periodic blood test).

Regarding the composition of the nanorobots, I don't have this nailed down firmly but at this point I'm thinking they would probably be carbon-based. If them containing a specific element would make the detection scenario more plausible, I may be able to work that in. For size, each nanorobot is about the size of a virus.

The time frame is the near future, so the test should either be one that currently exists, or would be likely to exist within the next decade or so.

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  • $\begingroup$ Well, the nanobots would have to be made of something, and probably need to be powered by something. That should throw the blood composition off at least slightly, depending on how many of them there are. Maybe that could be the beginnings of an answer? (I don't know what such things are commonly looked at in blood samples.) $\endgroup$ – a CVn Mar 24 '15 at 14:46
  • $\begingroup$ If they replicate in his blood stream then it would be plentiful enough that any decent blood test would uncover them. Are you just looking for a scenario in which the tests would be taken? $\endgroup$ – JDSweetBeat Mar 24 '15 at 14:46
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    $\begingroup$ A bizarrely high level of iron? significant trace silicon in the blood? carbon based is vague - do you mean nanotubes? those would precipitate in a centrifuge, so they'd notice a black layer of pure (or nearly pure) carbon when looking at the normally red blood and yellowish platelets. $\endgroup$ – Isaac Kotlicky Mar 24 '15 at 14:58
  • $\begingroup$ I didn't think of the idea that they might be visible in a test tube after centrifugation. That's intriguing, though I'd have to do some calculations to see if there would be enough of them, or how big the blood sample would have to be for there to be a visible amount. $\endgroup$ – nanoguy Mar 24 '15 at 15:31
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    $\begingroup$ If there is enough ferromagnetic material in the nanobots, an MRI might tear bits of the patient apart, That would indicate to most doctors that something odd was involved. $\endgroup$ – Darth Wedgius Mar 26 '15 at 20:44
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Copper Sulphate Densitometry

If you've ever donated blood then you know they prick your finger and drop your blood into a blue solution to test your iron level. If a person is too anemic, they can't give blood, so they need to test it before. The blue solution is copper sulphate dissolved to a specific density, this makes the iron in the blood sink in a measurable way.

For your character, this blood test might reveal abnormally high densities of what appears to be iron. Abnormal enough to facilitate further testing.

Complete Blood Count

Alternatively if the character thinks they are ill, or the abnormal results from above are a concern, their doctor might order a complete blood count. A sample of the blood will be analyzed either by a machine or a human technician counting the number of each of the different cell types in the blood. The nanobots would certainly be noticed in such a case.

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  • $\begingroup$ I think the complete blood count is the way to do it. It definitely seems like the nanorobots would show up right away, regardless of their composition. That's a great idea, thanks! $\endgroup$ – nanoguy Mar 24 '15 at 21:08
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    $\begingroup$ A top athlete might have a CBC done as a matter of routine; they wouldn't even have to have symptoms. $\endgroup$ – Monty Wild Mar 24 '15 at 23:11
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Assuming they use metals (specifically iron) in the blood to replicate they would cause a mild case of anemia. The individual would wonder as to why he has gotten this [usually genetically inherited] disease and they will take a blood sample. If the bots are plentiful enough they will be able to see them in the blood sample. They could (and probably would) also take a sample of bone marrow in which the bots likely manifest themselves.

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    $\begingroup$ In my scenario the nanorobots don't replicate. They could contain metals such as iron, though wouldn't steal iron from the person's blood. $\endgroup$ – nanoguy Mar 24 '15 at 15:18
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Not having any medical background, i still think that in a blood test at least often the blood is put in a centrifuge. Since your metallic nanobots are the densest stuff in the sample, they will all end up in the bottom of the test tube. If there are enough of them, they might even be noticeable with the naked eye.
If that fails... well. Then i am lost and need someone with more medical lab experience to help out :-)
By the way: A reason for the test might be a simple aids test, taken because your hero met a nice girl, and is a responsible figure. Or his spouse admitted an "accident" and they both decide to have a checkup.

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  • $\begingroup$ This is an interesting idea, but it is likely that virus-sized nanobots would not pellet faster than large objects such as cells no matter their density, due to their extremely small size. $\endgroup$ – March Ho Oct 21 '15 at 9:01
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Considering that they are made of metal and use a - proportionally - large ammount of it on its pure form, upon doing a simple x-ray, a large portion of the blood stream would block x-rays from passing as if the person was under a constrast x-ray.

From there, the medic could, via ruling out other diseases, detect that he got a "nanonrobot" infection and start treatment.

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Antibodies.

We don't actually need to do anything above and beyond modern technology in order to detect virus-sized objects. As long as the nanobots don't constantly mutate, evolution has already produced these powerful defences against virus-sized and smaller objects.

Molecular and cell biology labs routinely raise polyclonal antibodies against various proteins and viruses in the lab. These proteins can then be used in assays such as ELISA in order to detect the presence of the nanobot.

Due to the way antibodies work (random antibodies are generated by cells, and then selected for when encountering antigens), it is nearly impossible to create virus-sized nanobots that cannot be targeted by antibodies.

The only way this would theoretically be prevented is for the nanobots to evolve their "capsid proteins" much like real life viruses do to escape detection by the immune system. If your nanobot is incapable of evolving to stay ahead of the immune system, it will be detected and removed as quickly as any bacteria or viruses.

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