Patent ID: 7718784

Claim:
A unimolecular bistable molecular switch comprising a nucleic acid comprising a binding domain for a ligand, a framework and a signaling apparatus comprising an attached fluorophore and a quencher, and which alters reversibly between a state H, a state O and a state OL according to the reaction scheme, wherein each state of the switch consists of a single predominant secondary structure; wherein state H represents the molecular switch when the ligand binding domain (LBD) is hidden comprising a first stem loop portion which comprises a first stem segment and a second stem segment, wherein the first and second segments connected by a first loop portion form a first stem portion that disrupts the secondary structure of the LBD that is preferred for binding the LBD to the ligand; wherein state O represents the molecular switch when the LBD is open comprising a second stem loop comprising a second loop portion and a second stem portion and a third stem loop comprising a third loop portion and a third stem portion, wherein the third stem loop comprises the secondary structure of the LBD that is preferred for binding the LBD to the ligand, and wherein the second stem loop is connected to the third stem loop by a single-stranded nucleic acid segment, wherein the single-stranded nucleic acid segment corresponds to the first loop portion of state H; wherein state OL represents the molecular switch bound to the ligand, L, according to K 2 , the equilibrium constant for binding O to L; wherein the first stem loop portion comprises 2-5 mismatches which are compensated in O, whereby[O]/[H]is 0.01 to 0.1; wherein the signaling apparatus produces a different signal in state H than in state O or OL; and wherein the nucleic acid sequence is selected from the group consisting of SEQ ID Nos. 1, 2, 3, 4 and 5.