Provided are methods and devices for label-free detection of nucleic acids that are amplified by polymerase chain reaction. A solution containing the components necessary for a PCR is introduced to a microfluidic amplification chamber and an electric field applied to a confined region in which PCR occurs. PCR product generated in the confined region is detected by measuring an electrical parameter that is, for example, solution impedance. The devices and methods provided herein are used, for example, in assays to detect one or more pathogens or for point-of-care tests. In an aspect, the PCR product is confined to droplets and the assay relates to detecting an electrical parameter of a flowing droplet, thereby detecting PCR product without a label. In an aspect, the PCR occurs in the droplet.