In this work we report on a simple inertial microfluidic device that achieves continuous multi-particle
separation using the principle of Dean-coupled inertial migration in spiral microchannels. The
dominant inertial forces coupled with the Dean rotational force due to the curvilinear microchannel
geometry cause particles to occupy a single equilibrium position near the inner microchannel wall. The
position at which particles equilibrate is dependent on the ratio of the inertial lift to Dean drag forces.
Using this concept, we demonstrate, for the first time, a spiral lab-on-a-chip (LOC) for size-dependant
focusing of particles at distinct equilibrium positions across the microchannel cross-section from
a multi-particle mixture. The individual particle streams can be collected with an appropriately
designed outlet system. To demonstrate this principle, a 5-loop Archimedean spiral microchannel with
a fixed width of 500 mm and a height of 130 mm was used to simultaneously and continuously separate
10 mm, 15 mm, and 20 mm polystyrene particles. The device exhibited 90% separation efficiency. The
versatility of the device was demonstrated by separating neuroblastoma and glioma cells with 80%
efficiency and high relative viability (>90%). The achieved throughput of 1 million cells/min is
substantially higher than the sorting rates reported by other microscale sorting methods and is
comparable to the rates obtained with commercial macroscale flow cytomerty techniques. The simple
planar structure and high throughput offered by this passive microfluidic approach make it attractive
for LOC devices in biomedical and environmental applications.