Abstract: The invention encompasses methods and devices for diagnosing, theranosing, or prognosing a condition in a patient by enriching a sample in rare cells or other particles. The devices can be a microfluidic device comprising an array of obstacles and one or more binding moieties. The devices and methods can allow for enrichment of cells based on size and affinity, recovery of cells or other particles in locations on the microfluidic device, release of cells or other particles from the microfluidic device, flow of sample through the microfluidic device, and retention of rare cells or other particles from a sample obtained from a patient having a condition.