A compound of the general formula shown below, or a salt or solvate thereof: wherein: SBB analogues refer to the general structure or shown below: wherein: R 1 and R 2 are each independently selected from: i) hydrogen; with the proviso that R 2 is not hydrogen in general structure above and only one of R 1 and R 2 can be hydrogen in general structure above. ii) an optionally substituted alkyl group; iii) an optionally substituted aryl group; iv) an optionally substituted alkyl-aryl group; v) an optionally substituted aryl- alkyl group; or vi) R 1 and R 2 are linked so as to form part of a spiranic cycloalkane group, selected from cyclopentyl, cyclohexyl, cycloheptyl, cyclooctyl, cyclononyl or adamantanyl; R 3 is hydrogen or alkyl group; R 4 is hydrogen, or one or more of the following substituents: i) a halogen selected from F, Cl, Br and I; ii) NO 2; iii) CF 3; iv) SCH 3; v) an optionally substituted alkyl group; vi) a alkoxy group which optionally comprises one or more heteroatoms; Z is either Z 1 or Ar-Z 1, and Z 1 is selected from -O-, -NH-, -O(CH 2) n CH 2 O-, -(CH 2) q O- or -COO-, wherein n is an integer selected from 1 to 9, wherein q is an integer selected from 1 to 4, and wherein Ar is an aryl group optionally substituted with one or more of the following substituents halogen, alkyl, alkenyl or alkoxy; L is a bondor linker group that links Z to hapten; and hapten is selected from biotin, digoxigenin, 2,4-dinitrophenol, or fluorescein; R 1 and R 2 are each independently selected from: i) hydrogen; with the proviso that R 2 is not hydrogen in general structure above and only one of R 1 and R 2 can be hydrogen in general structure above. ii) an optionally substituted alkyl group; iii) an optionally substituted aryl group; iv) an optionally substituted alkyl-aryl group; v) an optionally substituted aryl- alkyl group; or vi) R 1 and R 2 are linked so as to form part of a spiranic cycloalkane group, selected from cyclopentyl, cyclohexyl, cycloheptyl, cyclooctyl, cyclononyl or adamantanyl; i) hydrogen; with the proviso that R 2 is not hydrogen in general structure above and only one of R 1 and R 2 can be hydrogen in general structure above. ii) an optionally substituted alkyl group; iii) an optionally substituted aryl group; iv) an optionally substituted alkyl-aryl group; v) an optionally substituted aryl- alkyl group; or vi) R 1 and R 2 are linked so as to form part of a spiranic cycloalkane group, selected from cyclopentyl, cyclohexyl, cycloheptyl, cyclooctyl, cyclononyl or adamantanyl; R 3 is hydrogen or alkyl group; R 4 is hydrogen, or one or more of the following substituents: i) a halogen selected from F, Cl, Br and I; ii) NO 2; iii) CF 3; iv) SCH 3; v) an optionally substituted alkyl group; vi) a alkoxy group which optionally comprises one or more heteroatoms; i) a halogen selected from F, Cl, Br and I; ii) NO 2; iii) CF 3; iv) SCH 3; v) an optionally substituted alkyl group; vi) a alkoxy group which optionally comprises one or more heteroatoms; Z is either Z 1 or Ar-Z 1, and Z 1 is selected from -O-, -NH-, -O(CH 2) n CH 2 O-, -(CH 2) q O- or -COO-, wherein n is an integer selected from 1 to 9, wherein q is an integer selected from 1 to 4, and wherein Ar is an aryl group optionally substituted with one or more of the following substituents halogen, alkyl, alkenyl or alkoxy; L is a bondor linker group that links Z to hapten; and hapten is selected from biotin, digoxigenin, 2,4-dinitrophenol, or fluorescein;