Capacity of PLL-coated devices. Like a buffer, the PLL-coated channel has the capacity to resists changes in pH. We determined this capacity by comparing the apparent delay in the output signals of a PLL-coated and an uncoated device (Fig. ). An abrupt change in pH is introduced a�er 15 min, wherea�er we determined the �me it takes for the output signal to change from 0 to 1 (i.e., the normalized values for a low to a high [I2]/[I1]). This 'delay �me', 𝑡𝑡 𝑑𝑑𝑑𝑑𝑑𝑑𝑑𝑑𝑑𝑑 , represents the �me required to recover 50% of the ini�al system with uncharged lysine residues in the channels (Supplementary Informa�on, S4.3). We measured this value in our experiments by subtrac�ng the delay �me of an uncoated device (𝑡𝑡 0 , wherein the delay of a signal arises from the �me required for transport from the device to detector) from the delay in the coated device (𝑡𝑡 1 ): 𝑡𝑡 𝑑𝑑𝑑𝑑𝑑𝑑𝑑𝑑𝑑𝑑 = 𝑡𝑡 1 -𝑡𝑡 0 .