Patent ID: 8318443

Claim:
A reagent for use in detecting an analyte, comprising a fluorescent energy donor and an energy acceptor, the energy donor and the energy acceptor being such that when they are sufficiently close to one another energy is non-radiatively transferred from the energy donor following excitation thereof to the energy acceptor quenching fluorescence of the energy donor, wherein the energy acceptor is of the formula: wherein: R 1 , R 2 and R 3 are each independently H, electron donating substituents, or electron withdrawing substituents or R 3 is attached to a linker structure, provided that at least two of R 1 , R 2 and R 3 are electron donating groups; R 4 , R 5 , R 6 , R 7 , R 8 and R 9 are each independently H, halogen, alkyl, aryl, O-alkyl, S-alkyl and R 10, R 11 , R 12 , R 13 , R 14 and R 15 are each independently hydrogen, O-alkyl, S-alkyl, alkyl, or one or more pairs of groups R 1 and R 4 and/or R 1 and R 5 and/or R 2 and R 6 and/or R 2 and R 7 and/or R 3 and R 8 and/or R 3 and R 9 and/or R 4 and R 10 and/or R 5 and R 11 and/or R 6 and R 12 and/or R 7 and R 13 and/or R 8 and R 14 and/or R 9 and R 15 is a bridging group consisting of aryl, alkylene, O-alkylene, S-alkylene or N-alkylene optionally substituted with one or more of SO 3 − , PO 3 2− , OH, O-alkyl, SH, S-alkyl, COOH, COO − , ester, amide, halogen, SO-alkyl, SO 2 -alkyl, SO 2 NH 2 , SO 2 NH-alkyl, SO 2 N-dialkyl, SO 3 -alkyl, CN, secondary amine or tertiary amine, provided that not all of R 10 , R 11 , R 12 , R 13 , R 14 and R 15 are hydrogen; wherein a linker structure is attached to the energy acceptor at R 3 , or where a bridging group is present optionally the linker structure is attached to the energy acceptor at the bridging group, the linker structure being formed by reaction of a linker element selected from an active ester, an isothiocyanate, an acid chloride, an aldehyde, an azide, an α-halogenated ketone and an amine with a reaction partner; and wherein the distance between the energy donor and the energy acceptor of the reagent is capable of modulation by a suitable analyte to be detected.