Flow experiments. Flow experiments were performed using a flow setup that consists of lowpressure pumps connected to a microfluidic channel. HCl (10 mM), NaOH (10 mM), PAA (21 mM), and PAH (21 mM) were prepared and transferred into glass syringes and mounted on low-pressure pumps and determine the feeding conditions, [X]feed. CETONI Elements software was used to program lowpressure pumps in the flow experiments shown in Fig. , and 4 (see Supplementary Information S5 for further information on the sequences used in each experiment). The same software was used to analyze the transmittance data (see Supplementary Information S4 for details of the experimental setup).