We developed colorimetric assays using unmodified gold nanoparticles (AuNPs) to directly detect unamplified or amplified microbial nucleic acids extracted from clinical specimens. The colorimetric assays are simple, rapid, and can sensitively detect different pathogens in clinical samples even under field conditions. The assays have successfully been used for the rapid, sensitive, and cheap detection of two pathogens with a high disease burden; hepatitis C virus (HCV), and mycobacterium tuberculosis (MTB).