A major challenge for diagnosing and monitoring the progression of amyloid-based diseases is the capability to distinguish between amyloid deposits that are associated with related, but distinctly different, diseases. Here, we demonstrate that Amino Naphthalenyl-2-Cyano-Acrylate (ANCA)-based probes can fluorescently discriminate between different types of amyloid deposits in brain. This discriminating behavior is due to the stabilization of the ground versus excited states of these probes as a function of the polarity of their microenvironment (i.e. within the binding pocket on the amyloid). This property makes it possible for the first time to estimate the inherent static relative permittivity of the binding pocket of each amyloid within tissue. The capability to selectively follow the deposition of specific amyloids in tissue may provide important information for therapeutic development that is not readily accessible from currently available technology.

A new family of fluorescent markers containing an Amino Naphthalenyl-2-Cyano-Acrylate (ANCA) motif has been synthesized and evaluated for its capability to associate with aggregated β-amyloid (Aβ) peptides. These fluorescent probes contain a nitrogen donor group that is connected via a naphthalene unit to an electron acceptor motif containing Water Solubilizing Groups (WSG). Chemical modifications were introduced to explore their effect on the capability of the ANCA-based probes to fluorescently label aggregated Aβ peptides. All synthesized probes bind to aggregated Aβ fibrils with low micromolar affinity and fluorescently stain amyloid deposits in human brain tissue from patients with Alzheimer’s disease. We found that structural modifications of the WSG site do not affect considerably the binding affinity. However, changes of the nitrogen donor group alter significantly the binding affinity of these probes. Also, increasing the hydrophilicity of the donor group leads to improved contrast between the Aβ deposits and the surrounding tissue in histological staining experiments.

We describe the design, synthesis and fluorescent profile of a family of self-calibrating dyes that provide ratiometric measurements of fluid viscosity. The design is based on covalently linking a primary fluorophore (reference) that displays a viscosity-independent fluorescence emission with a secondary fluorophore (sensor) that exhibits a viscosity-sensitive fluorescence emission. Characterization of fluorescent properties was made with separate excitation of the units and through Resonance Energy Transfer from the reference to the sensor dye. The chemical structures of both fluorophores and the linker length have been evaluated in order to optimize the overall brightness and sensitivity of the viscosity measurements. We also present an application of such ratiometric dyes for the detection of membrane viscosity changes in a liposome model.