A molecular rotor-based turn-on sensor probe for amyloid fibrils in the extreme near-infrared region

A fluorescence turn-on probe for amyloid detection in the extreme near-infrared region (>750 nm) is a highly desirable technological evolution from the view point of potential in vivo applications. Herein, we report a molecular rotor-based amyloid sensor probe which, on binding to the insulin amyloid fibril, registers a large turn-on emission in the near-infrared region, and records an exceptionally large red-shifted emission wavelength of ∼770 nm along with a Stokes' shift of ∼150 nm, the highest reported to date for any amyloid sensor probe, in the insulin fibril bound form, in the near-infrared region. Importantly, when bound to insulin fibrils, this probe also exhibits an exceptionally large red-shift of ∼120 nm in the absorption spectra, which enables the naked eye in vitro detection of amyloid fibrils.