Axis axon isolation device

As described in the Supporting Information (Figure S1), we used a homemade and modified commerical (AX150, AXIS™ Axon Isolation Device from Millipore) PDMS-microfluidic device to trap single cells. The fabrication used the standard soft lithography. The homemade microfluidic plate had two parallel channels (10.6 mm long, 1500 µm wide and 40 µm high), separated with a barrier. The barrier had 60 holes (each hole is 150 µm long, 10 µm wide, separation between two holes is 50 µm) to trap cells. Sample solution containing suspended cells was flowed in one channel while keeping a lower pressure in the second channel. This allowed trapping of one cell in each hole for binding kinetics measurement (~5 mins). The optics allowed imaging of two cells simutaneously. When one measurement was completed, the cells were released from the trapping holes, and new cells were trapped for repeated measurement. The sample and buffer flows were controlled with a drug perfusion system (SF-77B, Warner Instruments, Connecticut). The typical transition time between different solutions was about 1–2 seconds.