Suppose you wanted to trap DNA near a surface. Dissolved DNA is charged, so an electrical method might come to mind. Or, applying osmosis, you might try a semipermeable membrane. Heat, though, would probably be at the bottom of your list of exploitable physics. Thermal processes, such as convection in a cup of hot tea, tend to mix things up, not concentrate them. Worse, DNA starts to fall apart at a modest 80°C.
But if you’re not setting out to concentrate DNA, you’re freer, perhaps, to make the serendipitous discovery that heat can indeed do the job. That’s what happened to Dieter Braun of Rockefeller University in New York. Working as a postdoc in Albert Libchaber’s lab, Braun found that an infrared laser can generate thermal flows in a small container. If the container is the right size, those flows can boost DNA concentrations by factors of 1000 or more....
