Dr. David Hertzog - Stanford University, Stanford, CA
To create one of their fast-mixing microfluidics device, Dr. Hertzog and his team start by etching intersecting channels into a silicon chip. To begin, the channels are roughly 1 µm wide and 10 µm deep. They inject proteins and a denaturant into the lengthwise channel. The denaturant relaxes the proteins into stretched-out chains. At the same time they introduce a buffer into the channel that cuts across the chip. The denaturant diffuses strongly into the buffer because it has a high diffusivity relative to the proteins.
As a consequence, the proteins in the mixture concentrate, narrowing to a thin sheet approximately 0.1 µm wide. With the loss of the denaturant to the buffer, the proteins collapse and fold. When the confocal optical detector near the outlet scans down the mixer, it builds an image of the entire process. Minimizing the time needed for the denaturant to move into the buffer or "mixing time" stretches out opportunities for the tiny camera to record the proteins fold.