Synthesis and self-assembly studies of a new AIEE probe and its application in sensing amyloid fibrillation

We report self-assembly and photophysical properties of a new pyridothiazole based aggregation-induced-emission enhancement (AIEE) luminogen 4-(5-methoxy-thiazolo[4,5-b]pyridin-2-yl)benzoic acid (PTC1) and its application for the sensitive detection and monitoring of amyloid fibrillation. The self-assembling properties of the new AIEE probe are extensively studied by AFM and it was noted that as aggregation increases there is enhancement of fluorescence. The fluorescence of PTC1 is quenched upon addition of cupric (Cu2+) ions while the fluorescence is regenerated in the presence of amyloid fibers. AFM studies reveal that PTC1 self associate/aggregate to hairy micelle structures which gets disrupted on the addition of Cu2+ and again reassembles in the presence of amyloid fibers. Hence, the fluorescence quenching and regeneration may be attributed to disaggregation and AIE respectively. Further, a comparative analysis of the performance of PTC1 is done with the conventional ThT which confirms it to be a more sensitive probe for the detection of amyloid both in the presence and absence of Cu2+. Of note, a very simple, facile and cost-effective methodology for the detection of amyloid fibres is presented, wherein fluorescence quenching/enhancement can be visualized under UV without the use of sophisticated instrumentation techniques. To the best of our knowledge and literature survey, this is first report wherein the self-assembling properties of AIEE probe is studied extensively via microscopy and the photophysical properties compared w.r.t to the morphological transformations. The AIEE probe has been designed using an unusual pyridothiazole scaffold unlike the commonly used archetypal AIE scaffolds based on tetraphenylethene (TPE) and hexaphenylsilole (HPS) and hence, the work also has implications in designing new generation AIEE dyes based on novel scaffold reported.