An unnatural amino acid including a phosphate mimicking group for mimicking a phosphate group in phosphoamino acids and a protein phosphatase modifying group for covalently binding protein phosphatases. A probe for detecting disease including a phosphate mimicking group for mimicking a phosphate group in phosphoamino acids and a protein phosphatase modifying group for covalently binding protein phosphatases. A method for detecting the presence of disease by administering the unnatural amino acid, binding the unnatural amino acid with a phosphatase, detecting a signal, and detecting the presence of disease. A method of identifying a known protein phosphatase, and a method of identifying an unknown protein phosphatase. A method of making the unnatural amino acid.