Harvard and MIT researchers have developed a tool that is capable of identifying single cancer cells within a blood sample. 

Mehmet Toner, study leader and a professor of biomedical engineering at Harvard Medical School, and Brian Wardle, an MIT associate professor of aeronautics and astronautics, have created an instrument that could eventually allow doctors to see if cancer has spread from its original site faster than ever.  

Circulating tumor cells, which are cancer cells that escaped from the original tumor, can be difficult to find because a 1-milliliter sample of blood, which has tens of billions of normal blood cells, only contains "several" circulating tumor cells. 

"Of all deaths from cancer, 90 percent are not the result of cancer at the primary site," said Wardle. "They're from tumors that spread from the original site."

In response to this dilemma, Toner created a new microfluidic device capable of detecting these circulating tumor cells. He originally designed the device four years ago, and it worked by allowing a patient's blood sample to travel past tens of thousands of little silicon posts that are covered with antibodies. These antibodies stick to tumor cells, and any cancer cells that touch the silicon posts are caught and held in place. The problem with this prototype was that certain cells might never come in contact with the silicon posts at all. 

Toner has since made changes to the device with the help of Wardle, making it eight times better than the original. The microfluidic device now features porous posts instead of those that are solid, which were made using carbon nanotubes. The carbon nanotubes are small, hollow cylinders that have walls made of carbon atom lattices. A "forest" of these nanotubes have 10 billion to 100 billion carbon nanotubes per square centimeter, and are 99 percent air and less than 1 percent carbon.

Much like the original version, these carbon nanotubes are coated with antibodies that capture particular cancer cells. The device is also customizable, allowing researchers to attach different antibodies to the carbon nanotubes or adjusting the space between the nanotubes in order to catch objects of different sizes, from circulating tumor cells to viruses. 

The porous posts allow cells to run through them, much like a filter, offering greater chance of catching the cells researchers are looking for. 

Toner and Wardle's device is currently being tested in hospitals and is expected to be made available commercially "within the next few years." In addition, researchers hope to adjust the device for HIV diagnosis as well.

This study was published in Small.