Microfluidics in chemical biology

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Microfluidics in chemical biology uses tiny channels to move and mix fluids, letting scientists run chemistry and biology experiments on a miniature scale. The small size means you can use very little sample, run many experiments quickly, detect rare events, and control the environment around cells more precisely than with bulk methods.

Researchers have used microfluidics to crystallize proteins, perform PCR, sequence DNA, study protein expression in single cells, perturb embryonic development in model organisms, and culture cells, among many other studies.

A key consequence of miniaturization is a high surface area to volume ratio. This can help by guiding molecules to interfaces, but it can also cause unwanted sticking of proteins to surfaces. To minimize sticking, surfaces are often coated with surfactants or other chemicals.

PDMS (a silicone-based polymer) is the most common material for making microfluidic devices because it is compatible with biology: it is relatively inert, transparent to light, flexible, and allows gases to pass through. Surfaces can be made hydrophilic or hydrophobic as needed. For some experiments, glass is preferred. The standard way to make PDMS devices is soft lithography, which is cheap and versatile.

Fluid behavior at this scale is usually laminar (smooth, not turbulent). When two liquids flow side by side, they mix mainly by diffusion, which can create stable chemical gradients. Droplets can also be formed when an aqueous stream meets oil at a junction or through flow focusing; these droplets act as tiny reaction vessels.

Microfluidics makes it possible to study single molecules because the small volumes concentrate signals and can amplify them within nanoliter to picoliter spaces, improving detection. The combination of microfluidics and nanofluidics holds great promise for important discoveries in chemical biology.