Fig. 4. (A) Time-ordered Raman spectra of the IS 4-Mpy at the 1095 cm⁻¹ peak in the glycerol-assisted liquid film protection system. The corresponding time evolution of the frequency of the (D) 1095 cm⁻¹ peak. (G) The change of signal intensity I(t) at 1095 cm⁻¹ after achieving optimal hotspots compared to the maximum enhancement I_tp (the tipping point is indicated by the red bar in (A)). (B and C) Time-ordered Raman spectra of 10⁻⁷ M CV at 914 cm⁻¹ and 1174 cm⁻¹, respectively. The corresponding time evolution of the frequencies of the (E) 914 cm⁻¹ peak and the (F) 1174 cm⁻¹ peak. (H and I) The change of signal intensity I(t) at 914 cm⁻¹ and 1174 cm⁻¹ after reaching optimal hotspots compared to the maximum enhancement I_tp (the corresponding tipping points are indicated by the green bar in (B) and purple bar in (C)).