Oscillatory inertial focusing in infinite microchannels

Area of Science:

• Microfluidics
• Biotechnology
• Particle Manipulation

Background:

• Inertial microfluidics is a passive, precise, high-throughput method for manipulating and sorting microparticles.
• Current applications are limited to larger bioparticles (e.g., blood cells, tumor cells) due to device length and pressure requirements for smaller particles.
• There is significant interest in manipulating smaller bioparticles like bacteria, viruses, and exosomes.

Purpose of the Study:

• To develop a method for inertial focusing of micron-scale particles, including bacteria and nanoparticles.
• To enable particle manipulation at extremely low particle Reynolds numbers (Re < 0.005).

Main Methods:

• Utilized oscillatory microfluidics to achieve inertial focusing in effectively 'infinite channels'.
• Demonstrated focusing of synthetic particles as small as 500 nm and the bacterium *Staphylococcus aureus*.
• Characterized the physics using a Peclet-like dimensionless number (α).

Main Results:

• Achieved inertial focusing of submicron particles, previously unattainable with steady-flow inertial microfluidics.
• Demonstrated manipulation of particles at Re < 0.005, significantly lower than the ~10⁻¹ limit of steady flows.
• Identified that α >> 1 is necessary to overcome diffusion and enable inertial manipulation.

Conclusions:

• Oscillatory microfluidics extends inertial manipulation to smaller particles and lower flow regimes.
• This technique opens new possibilities for biomedical applications involving bacteria, viruses, and nanoscale blood components.
• The dimensionless number α is a critical parameter for inertial manipulation in this new regime.