2.6. Using Sous Vide Immersion Heaters to Create a Portable and Low-Cost Alternative to Circulating Water Baths Used in Laboratories

We have previously devised a low-cost alternative to a thermal cycler using the thermos thermal cycler (TTC), a PCR method using thermos cans as insulated water baths to create a semi-automated low-cost alternative to conventional thermal cyclers to be used in low resource settings and small laboratories [11,12]. Water temperature was maintained at denaturation and annealing/extension temperatures for the duration of each PCR run without active heating and cooling control.

For the current work, to achieve a steady circulating water system with consistent temperatures for denaturation and annealing/extension steps, we used two sous vide immersion heaters purchased at USD 99 each (Anova Culinary, 800 watt) to heat the water in two 6 quart clear food storage containers (Rubbermaid) to 55 °C and 95 °C, both of which are common PCR annealing/extension and denaturing temperatures (Figure 1). The temperature of the annealing/extension bath was first lowered to 53 °C during the reverse transcription step. We have previously determined that the water bath temperature remained steady at a set temperature (97 °C and 60 °C), with only 0.1 °C of variation (Figure S1). The sous vide immersion heater is a medium-sized device that can be securely clamped onto the edge of the food storage containers. Its steady heating and water circulation functionality results in a well-maintained, even temperature throughout the bath for long periods of time. We were able to measure the temperature throughout the heating duration using a temperature data logger (HH147U, Omega Engineering, Norwalk, CT, USA).

Water bath setup for SARS-CoV-2 detection using reverse transcription polymerase chain reaction (RT-PCR). Sous vide immersion heaters provided sufficient and consistent temperatures for RT, denaturation, and annealing/extension steps. A Raspberry Pi controlled a servo motor that moved the PCR tubes between the baths with a cell phone app via Wi-Fi connection. Large containers enable large number of samples to be tested.