“…42 Other spectral mapping based on scanning microscopy methods, such as infrared scattering scanning near-field optical microscopy (IR-s-SNOM) 43,44 and tipenhanced Raman spectroscopy (TERS), may be an alternative tool. 45 We found that each blue structure undergoes a unique path to diverse types of red structure, where a pattern, e.g., a certain blue structure prefers to transform into a certain red structure, was detected. The result implies that the stimulus (heat, in this work) leaves a fingerprint to the PDA blue-to-red transition pathways.…”