Influence of poly-electrolyte multilayers on the relative rate of activation. We validated the change of the total mass as a func�on of the deposi�on of PEMs, using a technique called quartz crystal microbalance (QCM). Fig. shows that the change in resonance frequency (∆f) increases linearly as a func�on of the number of polyelectrolyte layers (real-�me data of QCM are appended to Supplementary Informa�on, Fig. ). We chose polystyrene sulfonate, PSS, as it can be considered a 'strong' polyanion (pKa= 2). That is, it ensures a permanent nega�ve charge in the pH range of our experiments (pH=3-10). We observed a smaller ∆f value for the first layer (which represents the interac�on between SiO2 and PLL) compared to the ∆f-values of subsequent layers (which represent the interac�ons between PSS and PLL). The ∆f value for the first layer can be used to validate that the concentra�on of available amine groups in a single-layer coa�ng is in agreement with simula�ons (Supplementary Informa�on, S5.5). We note that ∆f values for the subsequent layers in PEMs represent the polyelectrolyte mass as well as the water molecules intercalated between the layers, limi�ng the possibili�es to quan�fy the number of lysine residues per added layer. Overall, the linear trend shows that the concentra�on of PLL on the surface can be increased using PEM deposi�on. The effec�ve concentra�on of 'free' amine groups, however, may only be increased with one addi�onal layer of PLL (as these charges in subsequent layers are shielded due to the ion-ion interac�ons with PSS). We compared the devices comprising PEM coa�ngs (3, 5, and 13 layers) with devices with and without a singlelayer PLL coa�ng (Fig. ). The experiment is similar to the previously described procedure: An abrupt change in pH is introduced a�er 30 min, wherea�er we determined the �me it takes for the output signal to change from 0 to 1 at pH 8. This change in pH is then followed by the recharging of the surface, thus recovering the acidic condi�on (pH 3), and the cycle was repeated 3-5 �mes (Supplementary Informa�on, S6). We found that the delay �me did not change significantly for PEMs with more than three layers. In accordance with the linear trend observed in Fig. , a maximum PLL density on the surfaces is obtained by one addi�onal PLL layer (thus, PEM with three layers: PLL/PSS/PLL). Importantly, Fig. shows that the rate of the compe�ng ac�va�on and the charging step in the PEM-coated devices is significantly different compared to a single-layer device.