A microfluidic device moves tiny volumes of liquid through channels smaller than a millimeter. A drop of blood, a few cells, a picoliter of reagent. The scale is small, but the advantages are large. Less sample, less reagent, faster reactions, and precise control. Microfluidics is the plumbing of lab-on-a-chip devices and a growing field in its own right.

The physics at small scales is different. Laminar flow dominates, meaning fluids move in parallel layers without turbulence. Diffusion is fast because distances are short. Surface tension matters. Electrokinetics can move fluids without pumps. These properties enable precise control and novel functions. Droplet microfluidics, for example, generates thousands of uniform droplets per second for high-throughput screening.

Microfluidics is used in diagnostics, where a drop of blood can be analyzed for multiple markers. It is used in DNA sequencing, where microfluidic chips prepare libraries and amplify DNA. It is used in drug discovery, where cells are cultured and tested on chip. It is used in organ-on-a-chip devices that model human tissues. It is used in chemistry, where reactions are performed in droplets.

The field is interdisciplinary, combining engineering, physics, chemistry, and biology. The devices are often made from polydimethylsiloxane, a flexible polymer, using soft lithography. The technology is still maturing, but its potential is broad.