Pathogens and infectious diseases are typically detected using a technique called polymerase chain reaction, or PCR. The method involves rapidly heating and cooling DNA molecules from a biological sample in a process called thermal cycling. This results in the amplification of the target DNA into millions, and even billions of copies.
Scientists and physicians can then use the copies to identify the type of pathogen causing the infection. The problem is that most PCR tests can take up to an hour or more, and a physician's decision-making window is typically less than ten minutes.
A new device developed by researchers called DOTS qPCR, is faster, more efficient and less expensive than alternatives currently being used in clinics. The work is described in the journal Science Advances.
"With DOTS qPCR we are able to detect amplification and identify the infection after as few as 4 thermal cycles, while other methods are working with between 18 and 30," said the author. "We can get from sample to answer in as little as 3 minutes and 30 seconds."
DOTS qPCR stands for droplet-on-thermocouple silhouette real-time PCR. 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.