Abstract: Described herein in an embodiment is a diagnostic device for detecting the presence of one or more target nucleic acids (e.g., a nucleic acid of a pathogen, such as SARS-CoV-2 or an influenza virus). In some cases, the diagnostic device comprises a substrate comprising both a reagent delivery region comprising one or more reagents (e.g., one or more nucleic acid amplification reagents) and a lateral flow assay region configured to detect one or more target nucleic acids. The substrate may be removably or permanently coupled to an inner component that is movable relative to an outer component. The diagnostic device may further comprise a sample-collecting component coupled to the outer component and/or the inner component. In some embodiments, the inner component may be moved relative to the outer component in order to sequentially expose the substrate to the collected sample. In some cases, the diagnostic device may be used with a reaction tube comprising one or more liquids (e.g.