Motivation for Microfluidic Systems and Surface-to-Volume Ratio

Microfluidics deals with controlling very small volumes of fluids, typically in channels with dimensions from micrometres to hundreds of micrometres.

Motivation

1. Very small sample and reagent consumption.
2. Low operating cost.
3. Rapid analysis and reaction times.
4. High-throughput parallel processing.
5. Integration of sample preparation, reaction and detection.
6. Portable point-of-care diagnostic systems.
7. Precise control of fluid transport and cellular environments.

Surface-to-volume ratio

For a characteristic length $L$, surface area scales approximately as $L^2$ while volume scales as $L^3$. Therefore, surface-to-volume ratio scales as $1/L$ and increases strongly as dimensions decrease.

Consequences include:

• surface forces and adhesion become important,
• heat transfer becomes rapid,
• diffusion can dominate mass transport,
• capillary forces become significant,
• wall interactions strongly influence fluid behavior.

Thus, the high surface-to-volume ratio is one of the main reasons microfluidic systems behave differently from conventional fluidic systems.