Researchers are developing a system that uses magnetic beads to detect rare types of cancer cells circulating in a patient’s blood, an advance that could help doctors diagnose cancer earlier. It could also monitor how well a patient is responding to therapy.
While other researchers have used magnetic beads for similar applications, the new ‘high-throughput’ system has the ability to quickly process and analyse large volumes of blood or other fluids, said Cagri Savran, an associate professor of mechanical engineering at Purdue University.
He is working with oncologists at the Indiana University School of Medicine to further develop the technology, which recently was highlighted in the journal Lab on a Chip.
The approach is said to combine immunomagnetic separation and microfluidics. In immunomagnetic separation, magnetic beads about a micron in diameter are or coated (or functionalised) with antibodies that recognise and attach to antigens on the surface of target cells.
The researchers functionalised the beads to recognise breast cancer and lung cancer cells in laboratory cultures.
‘We were able to detect cancer cells with up to a 90 per cent yield,’ said Savran, who worked with Purdue postdoctoral fellow Chun-Li Chang and medical researchers Shadia Jalal and Daniela E. Matei from the IU School of Medicine’s Department of Medicine. ‘We expect this system to be useful in a wide variety of settings, including detection of rare cells for clinical applications.’
Previous systems using immunomagnetic separation to isolate cells required that the cells then be transferred to another system to be identified, counted and studied.
‘What’s new here is that we’ve built a system that can perform all of these steps on one chip,’ said Savran, also an associate professor of biomedical engineering. ‘It both separates cells and also places them on a chip surface so you can count them and study them with a microscope.’
Another innovation is the fast processing, he said in a statement. Other microfluidic chips are unable to quickly process large volumes of fluid because they rely on extremely narrow channels, which restrict fluid flow.
‘The circulating cancer cells are difficult to detect because very few of them are contained in blood,’ Savran said. ‘That means you have to use as many magnetic beads as practically possible to quickly screen and process a relatively large sample, or you won’t find these cells.’
The new design passes the fluid through a chamber that allows for faster flow; a standard 7.5-milliliter fluid sample can run through the system in a matter of minutes.
The beads are directed by a magnetic field to a silicon mesh containing holes eight microns in diameter. Because the target cells are so sparse, many of the beads fail to attract any and pass through the silicon mesh. The beads that have attached to cells are too large to pass through the holes in the mesh.
If needed, the cells can be flushed from the system for further analysis by turning off the magnetic field.
‘Not only can the cells be readily retrieved for further usage, the chip can be re-used for subsequent experiments,’ Savran said.