Figure 1.

Chemical structures of A) 4,4′‐diaryl‐2,2′‐bithiazole (DABTA) and B) ¹³C‐methylated PiB (¹³C−Me−PiB). The carbon atoms of the dimethylamine as well as the methoxy groups of PiB were ¹³C enriched. C) Schematic representation of the titration protocol to transfer the PET tracer molecule to pre‐formed Aβ(1‐40) fibrils for MAS solid‐state NMR experiments. D) Superposition of 1D ¹³C and ¹⁵N spectra of Aβ(1‐40) fibrils titrated with the DABTA molecule at different molar ratios. The spectra were acquired on a Bruker Avance III 750 MHz spectrometer at 3 °C, setting the MAS rotation frequency to 10 kHz. Subsequent spectra with increasing DABTA concentration were recorded by unpacking and re‐suspending the sample in a buffer containing an increasing concentration of BSA‐bound DABTA.