Reporter-nanobody fusions (RANbodies) as versatile, small, sensitive immunohistochemical reagents.

Sensitive and specific antibodies are essential for detecting molecules in cells and tissues. However, currently used polyclonal and monoclonal antibodies are often less specific than desired, difficult to produce, and available in limited quantities. A promising recent approach to circumvent these limitations is to employ chemically defined antigen-combining domains called "nanobodies," derived from single-chain camelid antibodies. Here, we used nanobodies to prepare sensitive unimolecular detection reagents by genetically fusing cDNAs encoding nanobodies to enzymatic or antigenic reporters. We call these fusions between a reporter and a nanobody "RANbodies." They can be used to localize epitopes and to amplify signals from fluorescent proteins. They can be generated and purified simply and in unlimited amounts and can be preserved safely and inexpensively in the form of DNA or digital sequence.