An exothermic chip for point-of-care testing using a forehead thermometer as a readout

We report an exothermic chip for quantitative point-of-care testing using a forehead thermometer as a readout. The chip has a capillary channel that directs an aqueous sample into an exothermic reservoir. NaOH powders are preloaded in the reservoir as the exothermic reagent. At the inlet of the capillary channel, a microvalve is fabricated using an aptamer-modified hydrogel which is responsive to a specific analyte. When the aqueous sample comes in contact with the hydrogel valve, the hydrogel shrinks due to the selective analyte-hydrogel interaction. The volume reduction of the hydrogel increases the capillary flow rate, and thus increases the heat produced by NaOH dissolution. A forehead thermometer is used to measure the temperature increment which is correlated with the analyte concentration. Using this method, heavy metal ions (Hg²⁺ and Pb²⁺) in different real samples are quantitatively analyzed.