“The mouse bioassay is primitive, but remains the gold standard due to its sensitivity,” says Greg Sommer (8621). “Our SpinDx botulinum assay vastly outperformed the mouse bioassay in head-to-head tests, and requires absolutely no animal testing. Plus there are a lot of advantages in terms of cost and speed. Our test can be run in under 30 minutes, compared with days for the mouse bioassay.”
The botulinum assay uses the same lab-on-a-disk platform (SpinDx) as the radiation biodosimeter developed by Greg, Ulrich Schaff, and Chung-Yan Koh (both 8621). That device can perform protein measurements, white blood cell counts, and DNA testing, giving a rapid and detailed picture of radiation exposure (see Lab News, May 6, 2011).
The project received National Institutes of Health funding to adapt the lab-on-a-disk platform for toxin diagnostics. While botulism is quite rare — only about 145 cases are reported in the United States each year, according to the Centers for Disease Control and Prevention — the lethality of the toxin makes it an attractive candidate for bioterrorism.
“A very small amount in the food system could harm a lot of people,” says Greg. “This isn’t an assay with a large commercial market, therefore it’s not something that industry is going to take on. So this is where we, as a national lab, step in and fill the gap.”
There are several reports of botulinum having been weaponized by terrorists and nations at war, most notably by terrorists in Japan in the early 1990s as well as by Iraq during the Persian Gulf War. While the toxin has not yet been successfully deployed as a bioweapon, those working in national security are trying to get ahead of the problem with vaccines and therapeutics, as well as diagnosis and prevention. Additionally, botulinum is being used more frequently for therapeutic and cosmetic uses (Botox), creating greater risk for misuse.
Remarkably simple platform
The goal, says Greg, is to create a handheld, point-of-care device that can be used in the field by emergency responders. The SpinDx platform has several advantages for such a scenario. For one, it’s remarkably simple.
The device works just like a CD player, using a spinning disk to manipulate a sample.
“You just mix your sample and spin, says Ulrich. The device is very reproducible and reliable.”
Another advantage is the ability to process samples in virtually any form, which is especially important when testing for a food-borne toxin. If you prepare your sample correctly, this device can read it,‖ says Chung-Yan.
In a recent demonstration, he was challenged to test what was basically a continental breakfast — milk, half-and-half, yogurt, honey, hot chocolate mix, cinnamon, canned meat, peanut butter, and a raspberry vinaigrette salad dressing. “Milk and honey are difficult because they are viscous and opaque, plus honey has bee proteins that can interfere,” he adds. “Foods with a lot of fat — again, milk as well as peanut butter — are also traditionally hard to work with.”
Through a lot of trial and error, Chung-Yan made improvements to the assay that enabled it to handle thick, viscous food substances and increased its sensitivity under these challenging conditions. Collaborators at the USDA provided high-quality botulinum antibodies that bind with high affinity, enabling the higher sensitivity.
That ability to process so many food substances makes the device relevant for food safety testing. About 15 percent of botulism cases are food borne, usually related to home canning. In 2007, 14 people in seven states contracted botulism from hot dog chili sauce due to faulty manufacturing equipment at a food plant in Augusta, Ga.
“Food processing plants are looking for something that can be integrated into their assembly lines,” says Greg. “Our device will be suitable because it’s fast, inexpensive, and simple to operate.”
Tip of the iceberg
But botulism is just the tip of the iceberg. With proof-of-concept on the botulinum toxin, the team is turning its attention toward other toxins as well as pathogens, bacteria, and viruses. While the focus is on biodefense, Greg also sees the SpinDx device becoming a regular medical diagnostic tool.
“Ideally, this device would have a routine clinical application so medical personnel use it regularly,” he says. “The disks are consumable and assay-specific, so in an emergency you would just switch to the right toxin disk.”
The team is currently developing a deployable prototype to run the assays. The goal is a fully integrated, automated device ready for field testing.
“We’ve done most of our testing in a benchtop setting, where we spin the sample on the disk and then read it out on a microscope,” he says. “The next step is to automate those processes and get the system into users’ hands. This technology has a lot of potential for so many applications.”