DNA and RNA can be used to construct artificial nanodevices with strong potential for future biomedical applications. DNA nanodevices can function as biosensors, which detect and report the presence of proteins and naturally occurring nucleic acids, such as mRNA or microRNAs. Complex sensors can be realized by supporting DNA devices with DNA-based information processing. Artificial DNA-based reaction networks can be created that amplify molecular signals or evaluate logical functions to report the simultaneous presence of several disease-related molecules. Other applications for DNA nanodevices are found in controlled release and drug delivery. DNA can be used to build nanocontainers for drugs or switchable hydrogels, which can trap and release compounds. For in vivo applications of DNA nanodevices, techniques for efficient packaging and delivery have been developed and the first examples of intracellular RNA-based nanodevices have already been demonstrated.