Biosensors, compositions comprising biosensors, methods of producing biosensors, and methods of using biosensors are disclosed. The biosensors comprise a fluorogen-activating peptide and a blocking peptide. The fluorogen-activating peptide and blocking peptide are covalently linked through a peptide linker. The blocking peptide associates with the fluorogen-activating peptide thereby blocking an active domain of the fluorogen-activating peptide when the linker is in an unmodified state. The peptide linker may contain an amino acid sequence that is specifically recognized as a modification substrate by a cognate enzyme. The fluorogen-activating peptide and the blocking peptide at least partially disassociate when the linker is modified by an enzyme, thereby allowing the fluorogen-activating peptide to bind a cognate fluorogen and modulate a fluorescence signal.