Patent ID: 7507395

Claim:
A method of staining a biological sample, comprising the steps of: a) adding a first compound to the sample, where the first compound having the formula wherein R 1 and R 2 are independently C 1 -C 12 alkyl that is optionally substituted one or more times by C 1 -C 6 alkoxy or halogen, provided that the alpha-carbon of the alkyl is not halogenated; R 3 and R 4 are independently C 1 -C 6 alkyl; R 5 -R 8 are independently hydrogen, halogen, C 1 -C 6 alkyl, C 1 -C 6 alkoxy, sulfonic acid, ester of sulfonic acid, carboxylic acid, ester of carboxylic acid, -L-R X , or -L-S C , where L is a covalent linkage, R X is a reactive functional group, and S C is a conjugated substance; provided that at least one of R 5 -R 8 is sulfonic acid, ester of sulfonic acid, carboxylic acid, ester of carboxylic acid, -L-R X , or -L-S C ; and b) incubating the sample for a time sufficient for at least some of the first compound to be converted to a second compound having the formula wherein R 1 -R 8 are as defined above, thereby staining the sample.