Litmus-type thermochromic and solvatochromic sensors prepared with α-synuclein amyloid fibrils and polydiacetylene

Litmus-type sensors capable of detecting temperature and organic solvents have been developed with α-synuclein amyloid fibrils and 10,12-pentacosadiynoic acid (PCDA). The PCDA molecules localized on the amyloid fibrils through either co-incubation with monomeric α-synuclein (AF/PCDA) or simple mixing with the pre-made α-synuclein amyloid fibrils (AF + PCDA) were photopolymerized with UV to exhibit blue color on paper. The paper sensors prepared with AF/PCDA and AF+PCDA showed distinctive sensitivities toward temperature and solvents. Whereas AF/PCDA were able to detect the higher temperatures between 55 °C and 90 °C by exhibiting the blue-to-red color transition on paper, the AF + PCDA-containing paper sensor was sensitive to the lower temperatures from 25 °C to 60 °C. The less tight binding of PCDA to amyloid fibrils and thus increased its molecular freedom would be responsible for the discrete thermal sensing property. The AF + PCDA paper sensor was also able to detect organic solvents with brief exposure to their vapors while the AF/PCDA sensor changed its color only after direct contact with the solvents in solution. The vapor-induced blue-to-red transition was dependent upon the duration of vapor exposure. In addition, the AF + PCDA sensor was demonstrated to successfully follow ascending temperature change by exhibiting the color transition from blue to red, which could allow the litmus-type sensor to monitor thermal history of materials in general and localize the spots previously exposed to heat. Taken together, the amyloid fibrils of α-synuclein are shown to be a decent template for PCDA to develop into the litmus-type thermochromic and solvatochromic sensors.