Microfluidic Mixing and Separation Strategies in LoC

Mixing strategies

Because microfluidic flow is usually laminar, turbulence is weak. Mixing is therefore achieved using:

1. Passive mixing: Channel geometry such as serpentine, herringbone, split-and-recombine, T-junction and chaotic advection structures increases interfacial area and diffusion.
2. Droplet-based mixing: Small droplets provide short diffusion distances and can be transported through channels.
3. Active mixing: External energy such as acoustic, magnetic, electric or pneumatic actuation disturbs the streams and enhances mixing.

Separation strategies

1. Filtration: Microstructures physically retain particles larger than a selected size.
2. Hydrodynamic separation: Channel geometry and flow conditions separate particles according to size or trajectory.
3. Dielectrophoresis: Non-uniform electric fields manipulate particles according to electrical properties.
4. Electrophoresis: Charged particles migrate under an electric field at different rates.
5. Magnetic separation: Magnetically labeled cells or particles are captured or deflected using magnetic fields.
6. Centrifugal/inertial methods: Curved or specially shaped channels create forces that alter particle trajectories.

These methods allow LoC systems to perform automated sample preparation and analysis with very small volumes.