Figure 1. Solar thermal PCR system.

(a), the benchtop component holds the lens, the PCR chip and a rotational stage. (b), Thermocouples on the chip are connected by a microcontroller to a smartphone. (c), a screenshot shows the app recording the temperatures over time. (d), the top of the PCR chip contains the mask and the thermocouples. (e), the bottom includes the absorber layer and the microfluidic channel, with marked regions for annealing, extension and denaturation (inset). (f), amplification over a range of concentrations. (g), amplification over a range of cycling speeds. The typical extension rate of Taq polymerase is 60–100 nucleotides/s at 72°C. Thus, 3 s should be sufficient for full extension of a 164 bp product. The design of our channel suggests that a minimum reaction time of 10 s/cycle is required. The band intensity began decreasing for reaction times faster than 20 s/cycle, and no band was observed for reactions faster than 10 s/cycle. Intensity values were normalized by a reference sample that was run in a conventional thermal cycler for 2 h.