The present invention is directed to devices for performing PCR and monitoring the reaction of a sample comprising a nucleic acid and a fluorescent dye. Illustrative devices comprise a heat exchange component for heating and cooling the sample, a control device for repeatedly operating the heat exchange component to subject the sample to thermal cycling, an excitation source for optically exciting the sample to cause the sample to fluoresce, a photodetector for detecting temperature-dependent fluorescence levels from the sample, and a processor configured to record and process emissions from the fluorescent dye.