Concentration of resorufin plotted as a function of time (symbols) in steps of 0.1 s, obtained from transmission measurements (at λmax=571 nm). The solution contains 9.8±0.2 μm resorufin and 8.8±0.2 μm H2 O2, with either 0 nm, 5.5±0.1 nm, 27.5±0.6 nm, or 55±1 nm HRP. The transmission data was plugged into Eq. (5) to find the concentration of resorufin. Experimental data points are reported every 5 s for clarity; the confidence band indicates the error for all data points. The measurements were repeated three times at each [HRP] value; the data in the figure shows the average value. The fits (solid lines) are obtained using a pseudo-first-order kinetics model (Eqs. 4E–4F) with K1=0 and K2=0. The best agreement between experimental data and the mathematical model corresponds to the case where [HRP] was 5.5±0.1 nm. Therefore, this concentration of HRP was used for all other kinetic experiments in the paper – K3 was found to be 56±7 m-1 s-1 when averaged over the three trials at that particular concentration.