Medical Device Concept Reduces Time to Diagnose Infections

When a patient arrives at a hospital with a serious infection, doctors have precious few minutes to make an accurate diagnosis and prescribe treatment accordingly; however a new diagnostic device may significantly reduce the amount of time necessary to diagnose tissue infections.

Pathogens and infectious diseases in state-of-the-art laboratories are typically detected using a technique called polymerase chain reaction, or PCR and this method involves rapidly heating and cooling DNA molecules from a biological sample in a process called thermal cycling and most PCR tests can take up to an hour or more, and a physician's decision-making window is typically less than ten minutes.

Bioengineers at the University of Arizona (Tucson, AZ, USA) have developed a method called droplet-on-thermocouple silhouette real-time PCR (DOTS qPCR). The technology relies on the measurement of subtle surface tension changes at the interface of a water droplet suspended in an oil medium. The water droplet, which contains the target DNA to be amplified, is moved along a heat gradient in the oil to begin the chain reaction. As more copies of the target DNA are produced, they move towards the oil-water interface, resulting in measurable changes in surface tension. Remarkably, the size of the droplet can be measured using a smartphone camera, providing a method to observe the course of the reaction in real time.

In infective endocarditis diagnosis, DOTS qPCR demonstrates reproducibility, differentiation of antibiotic susceptibility, sub-picogram limit of detection, and thermocycling speeds of up to 28 s/cycle in the presence of tissue contaminants. The DOTS qPCR has sample-to-answer times as short as three and a half minutes. A log-linear relationship with low threshold cycles was presented for real-time quantification by imaging the droplet-on-thermocouple silhouette with a smartphone. DOTS qPCR resolves several limitations of commercially available real-time PCR systems, which rely on fluorescence detection, have substantially higher threshold cycles, and require expensive optical components and extensive sample preparation.

Jeong-Yeol Yoon, PhD, a professor and senior author of the study, said, “With DOTS qPCR we are able to detect amplification and identify the infection after as few as four thermal cycles, while other methods are working with between 18 and 30. The system still works with relatively dirty samples. We can use very minimal processing and still make the detection in a short time. It's easy to use, smartphone-integrated and saves money and labor using expensive equipment. This technology has a lot of commercial potential, and we'd be happy to work with industry to bring it to market.” The study was published on September 4, 2015, in the journal Science Advances.

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