Piezoelectric Sensor Detects Deadly Infections


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Clostridium difficile bacteria. Image: CDC / Lois S Wiggs / Wikimedia Commons

Clostridium difficile is a bacterium that infects more than three million Americans every year, resulting in severe intestinal distress and sometimes death. People who are especially vulnerable are the elderly and those with weakened immune systems. Clostridium difficile does not respond to standard antibiotics and can become life-threatening quickly—therefore it is critical to deliver the appropriate treatment as soon as possible.

However, current methods for identifying C. difficile are unreliable, time-consuming, and/or expensive. Toxins emitted by the bacteria actually cause the infection. Enzyme immunoassays (EIA) for these toxins are inexpensive, but only have a sensitivity of 60 percent. Automated genetic tests are sensitive but expensive. As a result, the standard approach calls for a two-step testing procedure combining toxin EIA and nucleic acid amplification testing (NAAT) such as polymerase chain reaction (PCR) and loop-mediated isothermal amplification (LAMP) to lower the cost. However, the two-step procedure takes time, which can delay timely treatment of the disease.

Dr. Wan Shih. Image: Drexel University

A Faster Alternative

Wan and Wei-Heng Shih, professors in the School of Biomedical Engineering, Science and Health Systems, and College of Engineering at Drexel University in Philadelphia, PA, are developing a new piezoelectric sensor that can detect C. difficile easily and quickly, without expensive equipment. This technology eliminates the need for multiple steps, is inexpensive and portable (allowing for testing in the field), and delivers results in 30 to 40 minutes.

The key part of the technology is a tiny ceramic plate about a millimeter long, half a millimeter wide, and thinner than a strand of hair. “It works like the piezoelectric tuning forks that keep quartz watches ticking on time,” says Wan Shih. “The plate is very thin with a crystalline structure that facilitates electrically driven oscillation. The slightest change to this structure results in a change in the pitch of the oscillation.”

The husband-and-wife team has modified the surface of the crystals on the plate so they can catch certain DNA molecules. When the plate has captured only a few molecules of C. difficile taken from a stool sample, its vibration changes, letting technicians know C. difficile is on the plate. This is a one-step molecular stool test that does not require isolation or amplification of the DNA from the stool because of the unprecedented sensitivity of the piezoelectric plate sensor.

“Our plate sensor gives us an advantage over tests on the market right now for C. difficile, which require a complicated process of isolating and amplifying DNA from a sample before the infection can be confirmed,” says Wan Shih. “These tests also require expensive equipment that isn't available in 80 percent of hospitals, so the samples have to be sent off to a lab.”

A Promising Future

This tiny piezoelectric sensor will very likely provide a rapid and inexpensive molecular test for Clostridium difficile infection (CDI) that not only can detect the infection, but also assess its severity. Patients with CDI must be isolated to prevent it from spreading and also receive aggressive treatment. Because most hospitals don’t have the necessary equipment for quick and accurate testing, they are more likely to treat the disease based on the symptoms, or an inaccurate toxin test, which can lead to improper use of antibiotics, which can increase patient mortality and spread the disease.

“No current molecular tests can detect CDI and assess CDI severity at the same time,” Wan Shih says. “A rapid and inexpensive CDI molecular test that can detect the infection and assess severity will allow physicians to quickly treat and manage CDI patients for improved patient outcomes, while keeping the infection from spreading,” she adds.

The Shihs intend to develop the first prototype of their sensor and move forward with clinical trials. They also plan to explore adapting the sensor to detect other infectious diseases through their own startup company, Lenima Field Diagnostics. “If we can one day tailor the sensor to detect other diseases, it can be used for point-of-care applications for diseases that need to be treated immediately or could be fatal,” says Wan Shih.

Mark Crawford is an independent writer.

Learn about the latest trends in medical diagnostics at ASME’s Global Congress on NanoEngineering for Medicine and Biology.

No current molecular tests can detect CDI and assess CDI severity at the same time.

Prof. Wei-Heng Shih,
Drexel University

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August 2015

by Mark Crawford, ASME.org