Use of bacterial carpets to enhance mixing in microfluidic systems

We demonstrate that flagellated bacteria can be utilized in surface arrays (carpets) to achieve mixing in a low-Reynolds number fluidic environment. The mixing performance of the system is quantified by measuring the diffusion of small tracer particles. We show that the mixing performance responds to modifications to the chemical and thermal environment of the system, which affects the metabolic activity of the bacteria. Although the mixing performance can be increased by the addition of glucose (food) to the surrounding buffer or by raising the buffer temperature, the initial augmentation is also accompanied by a faster decay in mixing performance, due to falling pH and oxygen starvation, both induced by the higher metabolic activity of the bacterial system.