Vanderbilt Team Develops Simple Medical Test Prep Device

Extractionator prototype; the silver cube is the external magnet (Susan Urmy/Vanderbilt University)

Researchers at Vanderbilt University in Nashville are developing a medical collection and preparation system that promises to bring diagnostic testing to the poorest areas of the world. The device, called the Extractionator, is the product of Vanderbilt biomedical engineer Rick Haselton, chemist David Wright, and biochemist Ray Mernaugh.

Haselton, Wright, and Mernaugh received a $1 million grant from the Grand Challenges in Global Health, an initiative of the Bill and Melinda Gates Foundation to develop the system. One of the Grand Challenges priorities is point-of-care diagnostics, to encourage researchers to create technologies and components that assess conditions and pathogens at the point-of-care in the developing world.

Diagnostics become difficult if not impossible to administer in rural clinics that are often without trained technicians, sophisticated medical equipment, electricity, or even water. To meet these criteria the Vanderbilt team developed a simple device to prepare patient samples for testing, made up of a length of clear plastic tubing. The tubing is filled with liquid chambers separated by short lengths of air, and a number of tiny magnetic beads at one end.

Operating the Extractionator is about as simple as the device itself. When a patient sample is introduced into the end of the tube, the operator uses an external magnet first to coat the beads with the target material. The beads have special coatings that bind with the specific biological molecules needed for a given diagnostic test.

The operator then drags the beads through the air spaces, which the researchers call surface tension valves, into the subsequent chambers. Each of the sequential chambers contains special chemicals that remove molecules that interfere with the accuracy of the test.  As a result, when the beads reach the other end of the tube, they carry a purified and concentrated sample of the sort required for testing.

While the Extractionator and its operation may be simple, constructing the device for use in the field is more of a challenge. One issue involves the surface tension valves that keep the different liquid baths apart. These valves are formed by a specific balance between the surface tension of the liquid, the internal diameter of the tubing, and the electrical properties of the plastic.

One of the team’s current research goals is to identify the various physical features that effect the formation of these valves.  Another issue is the chemical make-up of the plastic, which is also critical because biological molecules stick to the surface of many plastics. Thus the researchers need to identify types of plastic that are chemical inert when brought into contact with the biological molecules.

In addition, there is the issue of the coating on the magnetic beads. The device so far uses customized coatings designed to pick up a single biomarker used for a specific diagnostic test. In real-life use, however, the coatings may need to be more robust. Mernaugh says that the researchers “want to develop a coating that will target 20 different targets in a single sample,” adding “That would produce a sample that can be used for a number of different tests.”

The researchers have tested the system with two potential applications — biomarkers for the Respiratory Syncytial Virus (RSV) and for malaria — and in each case found their device to be effective. They evaluated extraction and concentration of the RSV biomarker in the greatest detail and found the Extractionator worked as well as the commercially available lab-based kits.

“It’s low-tech, high-science,” says Wright.

Read more:

• Gates Foundation, Grand Challenges Canada Fund TB Diagnostic
• Gates Grants Fund Malaria Modeling Device, Culture System

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