QCM measurements. Quartz crystal microbalance (QCM) measurements were performed using silicon dioxide (SiO2)-coated quartz sensors at 22 °C. The sensors were treated with a UV-ozone cleaner for 45 minutes, followed by immersion in a 2% sodium dodecyl sulfate solution for 45 minutes at 37°C, and then subjected to a 5-minute sonication. They were thoroughly rinsed with water and dried using a gentle flow of nitrogen. Subsequently, the sensors were treated again with UV-ozone cleaner for another 45 minutes. We rinsed the sensor surfaces with Milli-Q water, followed by PLL (0.5 g L -1 in water), PSS (0.5 g L -1 in water), and PLL. The real-time change in frequency and dissipation response between the 3 rd and 9 th harmonics were analyzed using Q-Sense. The additional experiments were performed using coated sensors to validate binding events in the presence of polyelectrolytes (PAA and PAH) in flow. See Supplementary Information S6 for further information.