Disclosed are compounds of the formula (I): wherein R3, R4, R5, R9, and R10 are selected from the group consisting of H and groups or atoms other than H, and R6 and R8 are halo or hydrogen; X1, X2, and X3 are independently O or S; provided that R9 and R10 are not simultaneously H, when all of X1, X2, and X3 are O; and of the formula (II) wherein R11-R14 are selected from the group consisting of H and groups or atoms other than H; X4-X9 are independently O or S; n and m are 0 or 1 but m and n cannot be 0 simultaneously; R15-R24 can be H or any substituent so long as the compound of formula II upon hydrolysis provides a fluorescent compound. These compounds are useful as substrates with high specificity for organophosphatase particularly human paraoxonase and bacterial organophosphorus hydrolase. Also disclosed is a method for detecting and/or measuring the paraoxonase activity in a fluid comprising contacting the fluid with a fluorescent substrate and measuring the fluorescence of the fluorescent product formed.