Provided herein are methods of detecting nucleic acids. The nucleic acid of interest may be detected by using Cas endonuclease to degrade substantially all nucleic acid in a sample except for the nucleic acid of interest, leaving the nucleic acid of interest isolated and amenable to detection. In related methods, Cas endonuclease complexes are used to protect the nucleic acid of interest while unprotected nucleic acid is digested, e.g., by exonuclease, after which the isolated nucleic acid of interest is detected.