Overview of the neutrophil chemotaxis device.

a. Microfluidic devices mounted on glass slides are observed on a microscope stage. In this picture, six chemotaxis devices are aligned side by side on the same glass slide. The left most device has inlet and outlet tubing attached and is filled with green fluorescent dye. b. Schematic of the microfluidic device. The device consists of a larger main channel and an orthogonal array of smaller channels. In the first step, the whole device, including the side channels, is primed with the chemoattractant solution. In the second step, neutrophils suspended in buffer are introduced in the main channel, washing out the chemoattractant from the main channel. The chemoattractant gradient is established by diffusion, in the longitudinal direction of the side channels, between the end of the side channels filled with chemoattractant and the main channel filled with buffer. Neutrophils inside the main channel follow a chemoattractant gradient and enter an array of side channels, where their chemotaxis migration speed is measured.