A chip to test white blood cell response quickly from just a drop of blood has been developed by scientists in the US.

Neutrophils are the most common white blood cells in the body. They play a key role in immune function, being drawn to a site of infection or injury by a chemical concentration gradient, effectively a trail of attracting molecules released by the distressed cells. The new chip, developed by Daniel Irimia and collegues at the Massachusetts General Hospital in Boston, can both isolate neutrophils from blood and monitor how they migrate in one rapid step.

Current migration-measuring techniques usually require a separate step to isolate neutrophils from blood samples, involving large sample volumes and lengthy procedures not suited to miniaturisation. Irimia's new method needs smaller volumes and avoids the extra step by capturing the neutrophils in the chip, in a chamber coated with cell adhesion molecules. 

A single drop of blood contains enough neutrophils to test the cells' migration abilities

Importantly, these binding interactions are weak. This means that the captured cells can move when a concentration gradient of a chemoattractant is applied, created using an arrangement of valves, inlets and outlets on the chip. The cells' movement is then monitored by microscopy, with images captured every six seconds.

The chip could find use in routinely testing individuals' neutrophil migration ability, says Irimia. This would help identify and monitor those with altered neutrophil function, such as children with repeated infections perhaps, he explains. It could also help find the balance needed between keeping neutrophils' protective effects and depressing their function when developing certain drugs, he adds.

Francis Lin, who also develops microfluidic devices for cell migration research, at Stanford University, Palo Alto, US, finds the work impressive. 'It is remarkable that it requires only a small drop of blood from the finger for initial cell loading,' he says. 'It allows repeated blood drawing from the same donor for more consistent experimental results or close follow-up tests,' he adds. 'This means it may find potential applications in systems biology-based research and personalised medical diagnosis.'

Irimia's team is now using the technology to explore several directions. A 'very exciting' collaboration, says Irimia, is with a burn surgeon. 'We want to test neutrophil function in patients with burn injury, where alteration of this function is known and has implications for infections and other complications.'

Frances Galvin