PCR (polymerase chain reaction) machines are used to amplify small amounts of DNA into billions of copies. This process can be used to detect the presence of genetic mutations, or of foreign DNA, such as from viruses or bacteria. For the reaction, a number of steps are repeated in a thermal cycle to increase the DNA to a detectable amount. Temperatures typically need to cycle between 50-98ºC (122-208ºF), which has traditionally been achieved with precision electronic resistive heating elements.
Researchers at the Cornell University have developed a solar-powered PCR device, called the KS-Detect, that instead uses a lens to harness sunlight as a heat source (similar to how you might have burned ants with a magnifying glass as a kid). The DNA samples are moved in and out of the light hotspot during cycling to control the temperature. When the cycles are done, a typical PCR dye called SYBR Green is added to the amplified DNA. The dye glows green under UV light if the test is positive for the sequence in interest. A smartphone is then used to take a photo of the glowing sample to analyze and determine the results.
The team reports that the device can complete a test in under 30 minutes and consume 80 mW of power, enabling a smartphone to run it for up to 70 hours. By removing the bulk of the electronics required in traditional PCR machines for heating, the KS-Detect could turn PCR diagnostics into a simpler and potentially cheaper point-of-care test.
Two members of the team, Li Jiang and David Erickson, are now in Uganda to test the KS-Detect in collaboration with Makerere University in Kampala. They are currently targeting the test towards detecting presence of a herpes virus that causes Kaposi’s sarcoma (hence the name KS), a slow-growing cancer that can spread and grow lethal unless treated quickly. It’s expected that the device can be expanded to run tests for presence of other diseases, like TB.
Paper in Scientific Reports: Solar thermal polymerase chain reaction for smartphone-assisted molecular diagnostics…