Some background: this question concerns iron oxide nanoparticles. Iron oxide nanoparticles are approximately 1 to 100 nanometers in diameter, as opposed to, say, a red blood cell, which is 10,000 nanometers across, meaning that they'll easily fit into blood vessels - you'll see how this is relevant in a bit. Moreover, small enough iron oxide nanoparticles exhibit superparamagnetism, meaning two things:

  • that their magnetism randomly flips direction when influenced by temperature (not particularly relevant to this question, as far as I know)

  • that they only exhibit magnetism when an external magnetic field is applied to them

My Evil Plan™ is to inject these nanoparticles into my minions. I can then control them by threatening them with a powerful magnet; if they do something I don't like, I can hit them with the magnet, magnetizing the nanoparticles. This will cause them to stick together in the blood of the unlucky minion, causing fatal blood clotting when enough of them stick together to form a blood vessel-blocking embolus.

Is my modus operandi possible in the scientific sense - i.e. are there any insurmountable physical barriers to making this happen?

Assume a modern-day or near-future (what could plausibly happen according to scientific theories) level of technology.

  • $\begingroup$ Note: again an implicit assumption that may or may not be true - the concentration of nanoparticles that's sufficient to block a major blood vessel is non-toxic on its own. After reading a bit, I'm afraid that's a failing assumption. $\endgroup$ Commented Dec 23, 2021 at 13:03
  • $\begingroup$ That's a bit of a Rube Goldberg execution method, isn't it? And clumping of nanoparticles in the blood won't necessarily cause clotting. You might be able to create a magnetic trigger that releases toxins, though. $\endgroup$
    – DWKraus
    Commented Dec 23, 2021 at 22:34

2 Answers 2


You will need to coat them in something hard to break down (otherwise they'll be excreted fast or used as iron reserves bound by proteins and out of the blood system (which they'll rejoin as haemoglobin).

You will also inject them in massive amounts, otherwise they won't reach a concentration large enough to block the blood vessels. At those concentration, we're in uncharted territory when it comes to their toxicity, even without the magnet applied.

Clearance Properties of Nano-sized Particles and Molecules as Imaging Agents: Considerations and Caveats.

Looks like, in general, NP sized <5nm are eliminated by kidney is a matter of hours, between 5nm and 60nm eliminated by liver (in bile) in matter of days, with larger sizes (and special chemistries) able to persisting for tens of days.

The iron oxide nanoparicles are somehow a bit more special

Given intravenously, iron oxide nanoparticles are primarily cleared from the blood by the RES [kidneys, that is]. The blood half-lives of the various iron oxide nanoparticles currently in clinical use vary from 1 h to 24-36 h [69]. However, specific biodistribution and clearance parameters depend on particle properties such as surface characteristics, shape, and size [71]. For example, USPIOs demonstrate biodistribution to lymph nodes in addition to the RES, whereas SPIOs do not have significant lymph node localization. [72]. Interestingly Neurberger et al. demonstrated that larger-sized MNPs are eliminated from the bloodstream faster than smaller-sized particles.


Interestingly, iron particles and coating materials may undergo different clearance mechanisms. Studies examining the clearance of the USPIO, Ferumoxtran-10 (Advanced Magnetics, Cambridge, MA), a 30 nm in diameter MNP with an iron oxide core coated with low molecular weight dextran, demonstrated that the dextran coating undergoes progressive degradation and was almost exclusively eliminated in the urine (89% in 56 days), with only a small amount excreted in the feces [74]. The iron contained in Ferumoxtran-10 was incorporated into the body iron stores and was later found in red blood cells in the form of hemoglobin [74]. Similar to endogenous iron, it was eliminated very slowly as evidenced by only 16-21% elimination after 84 days via hepatobiliary excretion (<1% urinary excretion) [74]. Similar behavior has been reported for SPIO feruxomides [74].

See also:

  • Toxicity of iron oxide nanoparticles: Size and coating effects
  • Uptake, distribution, clearance, and toxicity of iron oxide nanoparticles with different sizes and coatings
    Iron oxide nanoparticles (IONPs) have been increasingly used in biomedical applications, but the comprehensive understanding of their interactions with biological systems is relatively limited. In this study, we systematically investigated the in vitro cell uptake, cytotoxicity, in vivo distribution, clearance and toxicity of commercially available and well-characterized IONPs with different sizes and coatings. Polyethylenimine (PEI)-coated IONPs exhibited significantly higher uptake than PEGylated ones in both macrophages and cancer cells, and caused severe cytotoxicity through multiple mechanisms such as ROS production and apoptosis. 10 nm PEGylated IONPs showed higher cellular uptake than 30 nm ones, and were slightly cytotoxic only at high concentrations. Interestingly, PEGylated IONPs but not PEI-coated IONPs were able to induce autophagy, which may play a protective role against the cytotoxicity of IONPs. Biodistribution studies demonstrated that all the IONPs tended to distribute in the liver and spleen, and the biodegradation and clearance of PEGylated IONPs in these tissues were relatively slow (>2 weeks). Among them, 10 nm PEGylated IONPs achieved the highest tumor uptake. No obvious toxicity was found for PEGylated IONPs in BALB/c mice, whereas PEI-coated IONPs exhibited dose-dependent lethal toxicity. Therefore, it is crucial to consider the size and coating properties of IONPs in their applications
  • $\begingroup$ You seem to suggest that clotting should occur everywhere to have effect. I wonder could a relatively small magnet-induced clot particle be transported to the brain ? this proposed iron oxigen nanoparticle torture could be deadly within a few minutes ? $\endgroup$
    – Goodies
    Commented Dec 24, 2021 at 1:01

Your modus operandi is not better than threatening somebody with a knife or a sword: you will need to be in close proximity of the target to be able to put your words into action.


Because the intensity of a magnetic field quickly decays with distance, you won't be able to snap your fingers from your mansion and have minion Urguwandy killed somewhere in the world: you will need to find and bring her in close proximity of a magnet, and the magnet will need to be close to the target organ.

  • $\begingroup$ But its much easier to bring a magnet close to somebody. Just imagine someone just passing them on the street with a powerful magnet to kill them. Hell he could even perform CPR and be called a hero for attempting to save that person's life. Its also easier to hide. Imagine a couple of powerful magnets in their matrass so you can book it long before the murder takes place. Thats harder to do if you use a knife. $\endgroup$
    – Demigan
    Commented Dec 23, 2021 at 12:40
  • $\begingroup$ @Demigan Anyway, it's way easier to just inject a tiny pellet with 0.2mg of ricin than it is to go through all the trouble of injecting an amount large enough to clog major arteries but small enough not to kill the injected person outright. $\endgroup$ Commented Dec 23, 2021 at 13:00
  • $\begingroup$ A slight touch will do fine.. the clot particle will then be transported through the veins, eventually reaching the brain, or the lungs. A horrible death will follow. Don't try this at home with your minions, I would say. $\endgroup$
    – Goodies
    Commented Dec 24, 2021 at 0:56

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