By Erin Digitale
Photograph Courtesy of Manish Butte
Manish Butte wanted a better test for “bubble boy disease.” The weeks-long wait for the standard blood test results for the severe immune deficiency was too risky, leaving newborns vulnerable to life-threatening infections.
So Butte and his team invented a new medical sensor that could detect low T-cell counts, a hallmark of the congenital immune deficiency, in just 15 minutes. That’s great. But what’s even better is that the sensor is so versatile and inexpensive — the prototype cost just $60 to build — it could simplify diagnosis of a huge range of diseases.
Their device, called an integrated microfluidics-waveguide sensor, sorts and counts cells in small samples of blood and other body fluids. The thumbnail-sized sensor measures different types of white blood cells, a key component of the immune system, and could be used in doctors’ offices, newborn nurseries, patients’ homes, disaster sites and battlefields.
“Catching infections early is important for many patient populations,” says Butte, MD, PhD. He is an assistant professor of pediatrics at Stanford, a pediatric immunologist at Lucile Packard Children’s Hospital and the senior author of a paper describing the sensor that appeared in March in Biomicrofluidics. Stanford has filed for a patent on the device; the inventors are seeking a partner to commercialize the sensors.
He hopes those who have received organ transplants, suffer chronic kidney failure or are taking immune-suppressing drugs to treat rheumatoid arthritis could use the sensors to monitor their immune systems much in the way diabetics use glucometers to track their blood sugar at home.
Each of the body’s white blood cell types possesses different disease-fighting roles, and counting the cells helps doctors diagnose or monitor treatment of some diseases, including cancer and AIDS. But current cell-counting methods require fairly large blood samples and costly, slow laboratory equipment. In fact, the machines now in use cost tens of thousands of dollars.
The 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.
Among the new sensor’s applications could be allowing doctors to determine the cause of a runny nose. Taking a mucus sample from the patient, doctors could use the sensor to measure the white blood cells present. Elevation of one type of cells could implicate allergies, another could point to a sinus infection and a third could suggest a common cold.