Figure 4. Signal–response curve and kinetic model.

(a) Kinetic model used for fitting the experimental data. (b) Fluorescent intensity at 493 nm as a function of time on the addition of different amounts of ATP to a solution containing Au NP 1 ([TACN·Zn²⁺]=10±1 μM), probe A (3.7 μM) and a constant concentration of potato apyrase (0.017 U ml⁻¹). The solid lines represent the fit to a kinetic model. (c) Plots of the concentration of ATP (left axis) and free A (right axis) as a function of time for three different initial concentrations of ATP. The solid points indicate the period at which the concentration of free A is constant (<2% decrease with respect to the maximum value). The inset gives the duration of the time interval with a steady concentration of free A as a function of the initial amount of ATP.