Understanding the amyloid sensing mechanism of SYPRO Orange

Abstract

Amyloid fibrils, an aggregated form of proteins, are responsible for different types of neurological diseases. A constant effort is there for the search of a sensitive and selective probe for amyloid fibrils. Recently, it has been shown that a zwitterionic merocyanine dye, SYPRO Orange, can detect the amyloid fibrils with much higher sensitivity and with much preferred spectroscopic properties than present gold standard amyloid probe, Thioflavin T. In the present work, we have investigated the detailed photophysical properties of SYPRO Orange in different molecular solvents and solvent mixtures with wide range of properties to disentangle the fundamental processes that are responsible for its amyloid sensing activity. It has been shown that SYPRO Orange forms aggregates in water and results in extremely low emission quantum yield. The amyloid induced de-aggregation of SYPRO Orange is primarily responsible for enormous increase in its emission intensity upon binding with amyloid fibrils. Photophysical studies using steady state and time-resolved emission spectroscopy further enlighten us on the role of solvent polarity, solute-solvent H-bonding and solvent viscosity on its sensitivity towards amyloid fibrils. Thus, present results will be quite useful for the use of SYPRO Orange in different other spectroscopic applications.