Scientists have reinvented the technology that makes analyzing crime scene DNA and diagnosing infectious diseases possible—for 1/500 th the cost.
Today, we can distinguish human genetic material at crime scenes and detect the DNA of infectious agents in blood using a reliable, heat-dependent process called PCR. The catch is that PCR equipment usually runs into the multiple thousands of dollars—a significant barrier in resource-limited settings.
So scientists at the University of California, Santa Barbara designed a system that combines the wasted heat from an over-clocked computer with the imaging capacity of a mobile phone. It works just like regular PCR, but “for a fraction of the cost,” writes Faye Walker, an author of the study. Scientists eager to convert their PCs and phones to PCR machines can find the how-to guide published by members of Tom Soh’s lab in September’s issue of Analytical Chemistry.
“I think the cost effectiveness, particularly, is going to be a very attractive feature,” said Susan Montgomery, the epidemiology team lead of the Parasitic Diseases Branch at the CDC. “The equipment that’s needed for the way PCR is done in laboratories now is expensive.”
PCR works by mixing a miniscule amount of DNA with chemicals and running it through cycles of heating and cooling on a machine called a thermal cycler to copy the DNA billions of times. This amplification increases the amount of DNA to levels that, when mixed with fluorescent dyes, can be seen under UV light.
Kareem Ahmad, another author on the study, first considered harnessing a PC’s heat for biomedical research four and a half years into his PCR-intensive PhD. Ahmad had built a PC at home to watch movies and noticed the computer’s fan whirring loudly while he watched Netflix. When he checked the computer’s internal temperature, he saw it approaching 70˚ C. He remembers thinking, “I wonder if it could be hot enough to do PCR?”
Ahmad found inexpensive software online that could cycle the internal temperature of a computer, just like a PCR machine. The next day, he decided to run a PCR experiment using the computer instead of a thermal cycler as the heat source. “The second time I did that experiment, it worked, which was unlike every other project I had worked on up until that point,” Ahmad said.
Over the next two years, the PC-Phone-PCR (P3) system evolved until it eventually included a camera phone outfitted with a special filter and tubes pre-loaded with the necessary chemicals and fluorescent dye. Ahmad—who graduated with his PhD six months after the initial experiments—handed off the work to Faye Walker, “who did an excellent job of putting it across the finish line,” he said.
Using the final P3 product, the scientists in the lab could detect parasites in human blood by adding blood to the pre-loaded tubes, boiling them briefly, placing them in the computer’s heat sink, cycling the computer’s temperature, and—under UV or blue light—using the camera to detect the presence of the now-fluorescing parasite DNA. They then used the same computer that provided the heat source to analyze the photos and determine which tubes contained blood positive for parasite infection.
“I’m almost kicking myself for not coming up with it sooner, because it seems like—once you realize it—it seems like such a simple, obvious thing,” Ahmad said.
“I love the idea of making things with what you have, that solve problems that you have in the field,” said Dr. Darvin Scott Smith, chief of infectious disease and geographic medicine at Kaiser Permanente. Smith would like to see this technology tested in environments where the scientists anticipate it being used and eventually see it tested on multiple diseases.
Montgomery, the CDC epidemiologist, added that field-testing the P3 system, “will go a long way, I think, to pushing the argument forward that this is something that could be used in a disease control setting.”
Ahmad hopes the P3 system’s practicality will make it widely adoptable. “To me, what’s cool about this technology is that it’s not actually that sophisticated, and it’s not something that is beyond the reach of most people,” he said. “It’s something that’s almost democratic.”