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.