Electricity-free chemical heater for isothermal nucleic acid amplification with applications in COVID-19 home testing

Molecular detection of pathogenic nucleic acids from patient samples requires incubating biochemical reactions at specific temperatures to amplify DNA. This incubation is typically carried out with an electrical heater and a temperature controller. To reduce test cost, to eliminate the need for manufacturing incubators, which may require significant time, and to enable electricity-free operation, we use energetic compounds such as an Mg(Fe) alloy mixed with a phase-change material (PCM) that undergoes phase transformation at the desired incubation temperature. We dubbed this composite Energetic Phase Change Material (EPCM). When the EPCM is brought into contact with water, the magnesium alloy interacts with the water to produce heat. The EPCM heats up to its phase transition temperature. Any excess heat is absorbed as latent heat and the system is maintained at its desired incubation temperature, independent of ambient temperatures, long enough to facilitate enzymatic amplification. The EPCM together with colorimetric amplicon detection facilitates an inexpensive, disposable, point-of-need diagnostic test that does not require any electric power. We demonstrate the feasibility of our approach by detecting SARS-Cov-2 in saliva samples either without any instrumentation or with a palm-size CCD camera that enables us to follow the amplification process in real time.

Automated summary

The EPCM generates heat when in contact with water, allowing it to maintain a constant incubation temperature for enzymatic amplification. This enables a low-cost, disposable, electricity-free diagnostic test, demonstrated in detecting SARS-Cov-2 in saliva samples without instrumentation or using a palm-size CCD camera for real-time amplification monitoring.