Figure 1. Magnetically actuated protease sensors (MAPS).
Thermosensitive liposomes, consisting of the lipids DPPC, MSPC and DPSE-PEG, were encapsulated with magnetic nanoparticles and synthetic peptides. These peptide substrates are each coupled with a near IR dye, Cy7, as a urinary reporter, and an N-terminal biotin enabling streptavidin-bead based separation. Upon exposure to alternating magnetic fields (AMF), heat is dissipated by the co-entrapped MNPs due to hysteresis losses, which in turn melts the thermosensitive bilayer. The permeabilized membrane allows peptides to diffuse to the exterior where they are cleaved by proteases. Cleaved and uncleaved peptides clear into urine, where cleaved reporters are isolated using streptavidin-coated beads.