[+]Enlarge Computer Fan A computer’s heat sink (orange, left) can be used to heat the three stages of a polymerase chain reaction. In a low-cost blood test, researchers used the heat sink and a mobile phone app (right) to detect the DNA of a pathogenic parasite. Credit: Peter Allen

While people sit at their computers and watch movies or browse the Internet for cat videos, the processor chips in their machines generate heat. Now researchers have harnessed that heat to run the polymerase chain reaction (PCR) inside a computer. The method allowed them to detect miniscule amounts of DNA from a pathogenic parasite, and could lead to low-cost diagnostic tests in developing countries (Anal. Chem. 2014, DOI: 10.1021/ac5022419).

Researchers in H. Tom Soh’s lab at the University of California, Santa Barbara, developed software to cycle the temperature of a desktop computer’s central processing unit (CPU) to drive PCR’s three distinct steps. The team used the CPU as part of a test for the often difficult-to-diagnose Chagas disease, which is caused by the parasite Trypanosoma cruzi.

To test for the parasite’s DNA, the team adds an infected blood sample to a capillary tube preloaded with the PCR reagents and a fluorescent dye that complexes with DNA. The researchers also add dimethyl sulfoxide to the reagents to lower DNA’s melting temperature: To denature the DNA for PCR without this solvent, temperatures would need to reach 95 °C, which is too hot for a computer. They then place the tube in the fins of the CPU’s heat sink and run their temperature cycling program. The process amplifies the T. cruzi DNA, which is labeled by the fluorescent dye. The researchers use a cell phone app to quantify the amount of DNA based on the intensity of the glow of the tubes.

Using this method, they could detect as little as 0.1 femtogram/L of T. cruzi DNA, which is well below the threshold that leads to Chagas disease.