This sub-genre of science fiction has made its way into mainstream science journals. I argue that the science is sketchy and the fiction is disappointing. Submit your own Biophyctional Journal abstracts in the comments!
Science fiction rests on a compact between author and reader. The reader grants the author license to make some outrageous assumptions about the state of science and technology. In return the author spins an exciting yarn that may also hold some lessons about human nature. Recently a sub-genre of science fiction has made its entry into mainstream scientific journals. Again the authors ask readers to imagine that nature works very differently from what we know now, by factors of a million or up to 10 trillion. Then they speculate what might happen under those circumstances.
This particular context has become known as “magnetogenetics”: the dream of controlling specific proteins and cells throughout the body with magnetic fields. To make this dream a reality, one needs an actuator, namely some particle that couples the magnetic field to a biological function. Ideally that particle would be produced endogenously by biological cells under genetic control, and the most promising candidate for this role is ferritin. This is a large spherical protein shell, about 12 nm in diameter, into which the cell stuffs thousands of iron atoms, primarily to get rid of them. That iron confers ferritin with magnetic properties that could be exploited for magnetic control.
How would a magnetic particle like ferritin interact with the biology of the cell? Two modes have been considered: The magnetic field might tug on ferritin, which would transmit that force to an ion channel, alter the channel’s ionic conductance, and thus control the membrane potential. Alternatively, an oscillating magnetic field could be used to heat the ferritin, which would transmit that heat to a connected ion channel, again modifying the membrane currents.
This is where trouble arises: Based on our conventional understanding of physics and the measured properties of ferritin, its coupling to magnetic fields is much too weak to allow any of this. The discrepancies are huge, anywhere between 5 and 10 orders of magnitude, depending on what specific mechanism of action one considers . But that has not dissuaded a group of intrepid authors in this genre, who continue to put forward scenarios that wildly contradict how we think the world works.
In much of this literature the authors are perfectly aware that their explanations conflict with reality, and the contradictions are acknowledged front and center. Just a sampling of quotes:
- “…the heat dissipation in the nanoparticles should be of the order of 0.1 GW/g, a completely unrealistic value (6 orders of magnitude above the expected value)…” .
- “…the equivalent thermal resistances are 10 orders of magnitude higher than those predicted using the bulk thermal conductivity and the bead dimensions…” 
- “The thermal conductance of the water shell around the nanoparticle can be written as g* G where G is the macroscopic thermal conductance and g* is a scaling factor … leading to an estimated g* of 1e-13 for nanoparticle suspensions.” 
The latter fudge factor of 1013 appeared in the otherwise reality-based Biophysical Journal. Note how the postulated deviations from reality grow with time of publication, escalating by about a log unit per year. By now, a fictional factor of a million seems almost tame and sheepish.
Can you heat a single protein molecule?
The collection of papers cited above are about heating of nanoparticles. They espouse the notion that one can heat a protein or similarly small particle without the heat escaping into the surrounding medium over time periods of many seconds. A steady trickle of experimental reports claim that this is possible [5, 6, 7, 8]. By contrast, the conventional treatment of heat diffusion predicts that the heat escapes in less than a nanosecond, and the temperature rise from magnetically heating a single nanoparticle is utterly insignificant [9, 10, 1]. Hence the need to invoke these enormous fudge factors. But why should we accept an explanation of experimental results that starts with a complete rejection of conventional wisdom? The common fig leaf is that “heat transport on the nanoscale is not well understood”. That argument is just not tenable.
An unusual amount of scrutiny has been applied to nanoscale heat transport, because it matters intimately to a trillion-dollar global industry. The cell phone in your pocket is powered by chips with transistors only a few nanometers on a side . Electric current running through these devices generates substantial heat, and that heat must be carried away from the nanoscale of a transistor to the macroscale of your pants pocket. If there were any significant barrier to heat flow at the nanoscale, maybe as little as a factor of 10, these chip designs would be dead in the drawer. Fortunately nothing like that has emerged. One might wonder if there is something unusual about small particles floating in water, like ferritin in a cell. But an extensive review of experimental work concluded that “interpretation of the cooling rates of nanoparticles suspended in water and organic solvents does not appear to require any unusual thermophysical properties of the surrounding liquid to explain the experimental results” [12, 13]. On the theory side, it is now possible to compute full molecular dynamics simulations of heat flow that include every water molecule along the way; again, no unexpected heat barriers have emerged .
One has to conclude that the “single-protein heating” scenarios imagined in the Magnetofiction series simply can’t happen in this universe. The various claims in the literature surrounding single-particle hyperthermia must have other explanations, including the much more plausible one of human error.
What is the magnetic state of biogenic ferritin?
The latest title of the series  is instead about producing force or torque with ferritin. Here the author starts out by borrowing a factor of 10,000 from accepted reality, on the idea that the ferritin used in magnetogenetic applications to date  behaves very differently from all the other preparations of ferritin on which magnetic measurements have been made. He assumes that the ferritin core contains 4500 iron atoms that form a single superparamagnetic domain, such that they effectively respond to the external field as a cohesive magnetic spin. In reality, close to a century of measurements on natural ferritin suggest that it contains about 2400 iron atoms which assume a spin configuration that reduces rather than enhances the magnetic moment [17, 18, 19, 1]. Put simply, the experimentally measured magnetic susceptibility of ferritin is ∼10,000 times smaller than the author postulates here, and for some of the speculations in the article that factor gets squared.
What is the justification for departing so far from reality in this case? The reader is referred to reports about superparamagnetic behavior in so-called “magnetoferritin”. Chemists produce that material by emptying the native ferritin shell of its iron atoms and then refilling it with iron oxide under exotic reaction conditions, including precise control of oxidants at 70 deg C. The purpose of this unusual synthetic chemistry is precisely to produce nanomagnets with high magnetic moments, because biological cells don’t naturally do that. There is no reason to think that this material bears any resemblance to the biogenic ferritin construct used in all of the magnetogenetic applications to date. Indeed the creators of that construct  emphasized that it looks and behaves just like natural ferritin. But as the saying goes: “If it looks like a duck and walks like a duck and quacks like a duck, then it probably flies ten thousand times faster than a duck.”
New opportunities in creative science writing
Until recently this brand of speculative fiction was relegated to fringe publications. Why is it now breaking into mainstream Biology journals? Remember, we are not talking about string theory, where wild speculation is considered essential to progress. By comparison, heat flow is a perfectly stable and settled area of science. Perhaps classical physics just doesn’t have a big constituency among today’s journal editors. Would the reaction be different if the outrageous assumptions affected a more biologically sensitive subject? Imagine a genetics article whose discussion section starts with “We suppose that the human genome contains 1000 bases.” Or a paper on evolution that explains the observations with “All our results are consistent with the idea that the Burgess Shale is 1000 years old.” Would these articles get sent out for in-depth review? No-one has tried … until now.
Which brings me to a positive aspect of these developments: There is room for much more exciting fiction in this domain. Either of the two scenarios above (which depart from reality by only 6 log units) would make for fascinating consequences. Or imagine that we were wrong about the speed of light, and it’s actually the same as the speed of sound (6 log units again). One could explain so many things this way! Story lines come to mind that are much more enticing than the limited prospect of heating or wiggling a protein molecule by magnetic fields. So if you feel inspired, write your own Biofiction story, starting with an abstract (<150 words), and send it along in the comments. Be bold! And when you’ve finished the full length article, just submit it to your favorite Biology journal.
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