To accomplish microTetris, we use the technique of optical trapping (explained elsewhere on our group's webpage) to hold the glass beads in place. In short, an optical trap is a laser beam which is focused to a very tiny spot (1 micrometer = about 1/1000th of a millimeter) by a strong lens, usually a microscope's objective lens. This focus appears to act as an attractor point, in which small particles like our 1-micrometer glass beads (but also cells or bacteria) can be sucked and from which they cannot escape. This tool, also more figuratively referred to as 'optical tweezers' is nowadays indispensable in biophysical research. It is being used to push cells together to monitor their elastic properties, or to stretch single molecules of DNA until the DNA helix unwinds or breaks, or to measure the forces of the 'motor' that propells bacteria through their surroundings. In fact, we could add a lot more things to this list without being complete.



In our Tetris case, a device called an acousto-optic deflector (AOD) was used to computer-steer the trapping laser light very swiftly across the 42 bead positions as seen in the video—pretty much like the way a monitor steers its electron beam across the pixels on the screen. This was done fast enough for a bead to stay at its location while the laser was scanning the other positions. (At the end of the video, you can observe what happens if we suddenly switch off the laser light: the beads are no longer confined to their traps and can diffuse away easily.)

Just so you can appreciate what is going on in the video here, you have glass beads which are one million times smaller than a meter (micro-spheres) which are being manipulated using 'optical tweezers' to play a game of Tetris in a real physical field under a f-ing microscope! I pay homage to thee, powerful geek overlords!Now how the hell am I going to make an AOD ? Experiments begin soon at 'the lab' under an old microscope, a few laser pointers and .....well, microsound?