Subphthalocyanine-flipper dyads for selective membrane staining

The design, synthesis and evaluation of a subphthalocyanine-flipper (SubPc-Flipper) amphiphilic dyad is reported. This dyad combines two fluorophores that function in the visible region (420-800 nm) for the simultaneous sensing of both ordered and disordered lipidic membranes. The flipper probes part of the dyad possesses mechanosensitivity, long fluorescence lifetimes (tau = 3.5-5 ns) and selective staining of ordered membranes. On the other hand, subphthalocyanines (SubPc) are short-lifetime (tau = 1-2.5 ns) fluorophores that are insensitive to membrane tension. As a result of a Forster Resonance Energy Transfer (FRET) process, the dyad not only retains the mechanosensitivity of flippers but also demonstrates high selectivity and emission in different kinds of lipidic membranes. The dyad exhibits high emission and sensitivity to membrane tension (Delta tau = 3.5 ns) when tested in giant unilamellar vesicles (GUVs) with different membrane orders. Overall, the results of this study represent a significant advancement in the applications of flippers and dyads in mechanobiology. To increase responsiveness to membrane tension, subphthalocyanine-flipper dyads combine bright, long-lifetime mechanophores in ordered domains with bright, anisotropically, environment-insensitive, short-lifetime enhancers in disordered domains.