Tunable and precise miniature lithium heater for point-of-care applications.

Point-of-care diagnostic assays often involve multistep reactions, requiring a wide range of precise temperatures. Although precise heating is critical to performing these assays, it is challenging to provide it in an electricity-free format away from established infrastructure. Chemical heaters are electricity-free and use exothermic reactions. However, they are unsuitable for point-of-care multistep reactions because they sacrifice portability, have a narrow range of achievable temperatures, and long ramp-up times. Here we developed a miniature heater by modulating the lithium-water reaction kinetics using bubbles in a channel. Our heaters are up to 8,000 times smaller than current devices and can provide precise (within 5 °C) and tunable heating from 37 °C to 65 °C (∆T(RT) = 12 °C to 40 °C) with ramp-up times of a minute. We demonstrate field portablity and stability and show their use in an electricity-free multistep workflow that needs a range of temperatures. Ultimately, we envision providing better access to cutting edge biochemical techniques, including diagnostics, by making portable and electricity-free heating available at any location.