Heating and cooling by unconventional means: a multistage elastocaloric refrigerator and energy-flexible nucleic acid amplification devices

Abstract

Here we report unconventional ways to heat and cool common laboratory devices. First, we describe multiple tools that perform nucleic acid amplification but that may be heated by sunlight or other sources of heat. The application of these devices is cancer diagnosis in limited resource settings, where electricity may be unavailable. One device is microfluidic and performs the polymerase chain reaction, using sunlight to heat the sample to the three temperatures required for the assay. Another device is energy-flexible and may be powered by sunlight, flame, or electricity, and performs an isothermal nucleic acid amplification assay. These devices were deployed in Uganda during multiple field trials, and we report their performance under a diverse range of operating conditions. We tested 71 Ugandan patients for Kaposi's sarcoma using the isothermal device, and found 94% agreement with gold-standard laboratory equipment. Second, we describe a refrigerator that applies mechanical stress to shape memory alloys to achieve cooling (an elastocaloric refrigerator). Although elastocaloric cooling has been reported as one of the most promising alternatives to the vapor-compression cycle, the maximum temperature drop reported in any elastocaloric cooling system was only 7°C until this time. Here we report the first demonstration of a multistage elastocaloric refrigerator, where we achieved temperature drops up to 12.3°C below ambient. We also identify methods to enable multistage systems to operate at the same temperature span of single-stage systems but at higher coefficients of performance. Lastly, we tie the two above topics together by the demonstration of a thermal cycler that uses only heat (from any of sunlight, flame, or electricity) and shape memory alloys to autonomously achieve its temperature fluctuations. This mechanism may be used to perform the two-step variant of the polymerase chain reaction, and has demonstrated cycle times and temperatures comparable to commercial thermal cyclers. Heating of the device can be achieved in about 15 minutes, even when heated via sunlight.