Fig. 4: Resolving the photoswitching dynamics of a single 500 nm lipid vesicle by MIR near-field signal traces.
a Optical near-field amplitude image normalized to the surrounding D2O (s2 /s2, D2O) and d near-field phase image (φ2), recorded at 1603 cm−1 with 2 min acquisition time, directly before starting the MIR signal trace acquisition at the position of the cross, scale bars 500 nm. The recorded amplitude (s2 /s2,D2O) in (b) together with the phase (φ2) in (e) reveal the photoswitching dynamics of the eight switching events at a sampling time of tp = 500 ms. The symbols above (b) in combination with the dashed vertical lines indicate when the illumination wavelength was switched to the value written above. The blue and violet coloring of the signal traces mark the switching light’s wavelength at each point. The black curves are moving averages of the measured data, and the red curves are sigmoidal fits of the switching process of the form \({{{\rm{f}}}}\left(t\right)=\frac{L}{1+{{{{\rm{e}}}}}^{-\frac{\left(t-{t}_{{{{\rm{d}}}}}\right)}{\tau }}}+C\) as displayed in detail in Figs. S5 and S6. c Optical amplitude and (f) phase images taken directly after acquiring the near-field traces show that the vesicle remained stable in both position and signal strength, even after eight consecutive switching transitions, scale bars 500 nm.
