Biophys-is-sick-s
Today I burned microbes to death with LASERs. Experiment BP02: Optical Tweezers should be renamed BP02: The Sick Torture of Bacteria, because that’s basically what it is.
If you’ve ever seen that experiment where you levitate a ping-pong ball over the nozzle of a reversed vacuum cleaner, you’ve seen in action a similar principle to that behind optical tweezers; the only difference is that in this the ping-pong ball is replaced by a microscopic, transparent object, and the air blower is, in fact, a powerful LASER focussed through a microscope lens. The tiny, see-through objects are sucked inexorably to the centre of the beam of light, where you can then move them about as you please. All together now: “Whoopee for photon momentum!”
All very well if all you’re doing is moving about tiny polystyrene beads 1-2μm across.
However, the next stage is to move onto Vibrio alginolyticus, small ocean-dwelling bacteria which swim an impressive thirty times their body length per second by rotating little rope-like flagelli with a tiny molecular motor powered by Na+ ions. These bacteria (like most tiny things) are transparent, and so are sucked inexorably to the centre of the LASER beam when grabbed by the sadistic scientist. However, the difference between this and polystyrene is that the high-intensity light beam toasts the poor little saps to within a micron of their life during their ever-so-brief stay inside the Column of Optical Death.
What is even more twisted is that the purpose of the experiment is to measure the rotational speed of the molecular motor causing them to zoom along, and so their traumatic death throes are monitored for your convenience as a power spectrum on a computer screen, the moment of death immortalised forever in glorious two-dimensional graphics at a sampling rate of around 5kHz.
The final part of the experiment is to calculate the average percentage damage rate caused by frying the little chaps and chapettes in your LASER beam. It seems to somehow trivialise the passage into the otherworld if the net result of one’s hopping off the mortal coil is simply a number in a practical logbook.
On the pros side for utilitarian ethicists, for less than ten bacteria ruthlessly burned to death, several million others enjoyed a care-free few hours swimming about in a glucose-rich saline buffer solution.
Such is the lot of creatures too small to see in physics laboratories.