Patent ID: 7625758

Claim:
A method for detecting proteins in a medium having a pH of 5 or below, said method comprising contacting said medium with a compound having the formula: wherein: R 1 , R 3 , R 4 , and R 5 are members independently selected from the group consisting of H, OH, SO 3 − , C 1 -C 10 alkyl, C 1 -C 10 alkoxy, C 1 -C 10 alkyl substituted with halogen, and C 1 -C 10 alkoxy substituted with halogen; R 2 is a member selected from the group consisting of OH, OR 21 , and NR 22 R 23 wherein R 21 , R 22 , and R 23 are members independently selected from the group consisting of H, C 1 -C 10 alkyl, phenyl, and substituted forms of C 1 -C 10 alkyl and phenyl wherein the substituents are members selected from the group consisting of halogen and SO 3 − , or R 22 , and R 23 are combined to form a single C 4 -C 8 alkyl group such that R 2 is a N-containing heterocycle; R 6 and R 7 are members independently selected from the group consisting of H, C 1 -C 10 alkyl, and substituted forms of C 1 -C 10 alkyl wherein the substituents are members selected from the group consisting of halogen and SO 3 − , or R 6 and R 7 are combined as a single alkylene group, saturated or unsaturated, bridging the carbon atoms to which they are bonded to form a cyclic structure of 4 to 8 carbon atoms; n is 0, 1, 2, 3, or 4; and Q is a member selected from the group consisting of where * denotes the site of attachment, R 8 is a divalent radical selected from the group consisting of O, S, Se, NR 81 , and CR 82 R 83 , wherein R 81 , R 82 , and R 83 are members independently selected from the group consisting of H, C 1 -C 12 alkyl, C 1 -C 12 alkyl interrupted by a member selected from the group consisting of carbonyl and imino, C 1 -C 12 alkyl substituted with SO 3 − , and C 1 -C 12 alkyl interrupted by a member selected from the group consisting of carbonyl and imino and substituted with SO 3 − , R 9 , R 10 , R 11 , and R 12 are members independently selected from the group consisting of H, OH, SO 3 − , methyl, methyl substituted with halogen, or any two of R 9 , R 10 , R 11 , and R 12 are combined as a single alkylene group, saturated or unsaturated, bridging the carbon atoms to which they are bonded to form a cyclic structure of 4 to 8 carbon atoms, and R 13 is a member selected from the group consisting of C 1 -C 20 alkyl and C 1 -C 20 alkyl substituted with a member selected from the group consisting of CO 2 − and SO 3 − , while maintaining said medium at a pH of 5 or below and substantially avoiding the formation of covalent bonds between said compound and said proteins; and detecting association complexes of said compound and said proteins thus formed without removing unbound dye from said medium, thereby detecting said proteins.