“Zipper” Molecular Beacons: A Generalized Strategy to Optimize the Performance of Activatable Protease Probes

We report the proof-of-principle concept for zipper molecular beacons (ZMB) comprising an asymmetrical polyarginine/polyglutamate electrostatic "zipper" hairpin-linked fluorophore-quencher pair. The objective is to balance maximal quenching efficiency and optimal two-step activation (protease cleavage/zipper dissociation), while enhancing target cell uptake. This strategy also eliminates the peptide sequence dependence of conventional protease beacons. This ZMB concept is a generalizable approach to improve the functionality of a wide range of diagnostic/therapeutic probes through a simple switching of substrate sequences.