Figure 4.

Probe-dependent fs-TA signal intensity dynamics of the (a) ESA and (b) SE features following 400 nm excitation of the Ca²⁺-free (blue diamonds) and Ca²⁺-bound (red circles) REX-GECO1 biosensor. Individual data points are overlaid with the least-squares multi-exponential fits (solid curves, color-coded), the retrieved time constants and weighted amplitudes are listed accordingly. The spectral integration regions for the Ca²⁺-free biosensor’s ESA and SE bands are 520–532 and 581–604 nm, respectively. The spectral integration regions for the Ca²⁺-bound biosensor’s ESA and SE are 523–535 and 583–620 nm, respectively. The asterisks by certain amplitude percentages indicate the intensity rise components from the best fits.