Patent ID: 8883962

Claim:
A compound, comprising a sensor moiety, a first linker, and a first amino acid, wherein the first amino acid is a natural amino acid or a non-natural α-amino acid; and the sensor moiety is selected from the group consisting of wherein, independently for each occurrence, X 1 is —H, —F, or —Cl; X 2 is —H, —F, —Cl, —CO 2 R 1 , —C(O)-(first linker), -(first linker), —NR 1 -(first linker), or —S-(first linker), wherein at least one instance of X 2 is —C(O)-(first linker), -(first linker), —NR 1 -(first linker), or —S-(first linker); X 3 is —H, —F, —Cl, or —OR 1 ; R 1 is —H or alkyl; R 2 is —H or phenyl; R 3 is H, alkyl, or —CO 2 H; R 4 is H or alkyl; and X 4 is —C(O)-(first linker), -(first linker), —NR 1 -(first linker), or —S-(first linker).