Portable device can sort and count different cell types

Based on an integrated microfluidics-waveguide sensor, the device has particular potential for difficult-to-detect immune conditions.

The body has many types of white blood cells, each with different disease-fighting roles. White blood cell counts already help doctors diagnose some diseases and monitor treatment of others, including cancer and AIDS, but current cell-counting methods require fairly large blood samples and costly, slow equipment that can be operated only by trained laboratory technicians.

A team at Stanford led by Dr Manish Butte developed the sensor as a better way to screen newborns for severe combined immunodeficiency – a congenital illness commonly known as ‘bubble boy disease’. California’s current method for screening newborns takes three to six weeks to return results, by which time some affected infants could contract life- threatening infections.

By contrast, the new sensor has the potential to detect low T-cell counts, a hallmark of the disease, in a 15-minute test in the newborn nursery before a new baby goes home from the hospital.

According to a statement, the new sensor consists of a small, rectangular piece of glass impregnated with a strip of potassium ions. The potassium-impregnated glass acts as a ‘waveguide’ — laser light shone into the strip of glass is transmitted down it in a specific way, and the light emitted from the far end of the waveguide can be measured with a light sensor.

To operate the detector, a patient’s fluid sample is mixed with antibodies specific for the particular type of white blood cell to be measured. Each antibody is attached to a tiny bead of magnetic iron. Then, the sample is injected in a small channel on top of the glass waveguide. A magnet under the glass traps the labeled cells in the channel. The iron beads block a bit of the laser light that would otherwise pass through the waveguide, and this reduced transmission is measured by the light sensor at the far side of the glass.

‘Catching infections early is important for many patient populations,’ Butte said. ‘A low-cost way of counting cells could provide point-of-care diagnosis and monitoring for immune disorders, allergies, infections, AIDS, cancer and other disorders,’ said Butte.