2-((4-Azido-2,3,5,6-tetrafluorobenzoyl)amino)ethyl methanethiosulfonate is a cross-linker containing a thiol-reactive MTS group and a photoaffinity label 4-azido-2,3,5,6-tetrafluorobenzene (ATFB). ATFB is known to be a superior photoaffinity label that undergoes highly efficient C-H bond insertion on UV photolysis.