In one embodiment, the present invention relates to fluorescent nucleic acid constructs and methods of using these switchable constructs to rapidly screen for target molecule interactions. More particularly, an RNA/DNA chimera comprising a fluorophore-quencher pair and a nucleic acid construct is disclosed for the rapid screening of interactions between the HIV-1 nucleocapsid protein, NCp7, and a stem-loop region, SL3, of the HIV-1 RNA, or antagonists thereof. The compositions and methods disclosed herein can be used in preferred aspects of the present invention for diagnosing disease states, distinguishing the presence of infectious or toxic agents, drug discovery and design, and molecular electronic applications.