The PDMS-based substrate was immersed in the chosen NP dispersion for 10 min (Figure 1 a) and then rapidly dried by blowing off any remaining dispersion with compressed air. In another test, the microfluidic device and a syringe filled with the NP dispersion were connected with polytetrafluoroethylene tubes (inner diameter = 0.5 mm, outer diameter = 1.59 mm), and the NP dispersion was introduced into the device using a syringe pump (KDS100, KD Scientific, Holliston, MA, USA) at a constant flow rate (0.7 mL/h for polystyrene NPs; 0.7, 1.4, and 3.5 mL/h for exosomes) for 10 min (Figure 1 b). In the experiments that used polystyrene NPs, the flow rate was fixed at 0.7 mL/h to compare the adsorptivity in static and dynamic environments, while in the experiments that used exosomes, the different flow rates were used to investigate the adsorptivity in dynamic environments with different flow rates. The flow rate range and temperature (20 °C) were determined on the basis of previous studies concerning the handling of exosomes using microchannels [5 (link),21 (link)]. Because the ambient temperature in most laboratories is ~20 °C, this temperature was chosen for NP analysis. Subsequently, the PDMS-based microchannels were quickly peeled off, and their surfaces were promptly dried by blowing off any remaining dispersion with compressed air.
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