The device was functionalized in a three-step procedure using biotin-avidin chemistry (fig. S1D). Initially, the device channels were washed with PBS buffer. Next, the channels were sequentially incubated with solutions of biotinylated BSA (200 μg/ml) for 2 hours, streptavidin (100 μg/ml) for 1 hour, biotinylated anti-human CD63 antibody (10 μg/ml) (BioLegend, 353018) or biotinylated anti-human MCSP antibody (10 μg/ml) (MACS Miltenyi Biotec, 130-099-049) for 2 hours, and 1% (w/v) BSA for 0.5 hour at RT. After each incubation step, the channels were washed with PBS buffer to remove excess reagents.