Fusion 200 touch

The substrate solution was prepared by dissolving N-α-benzoyl arginine ethyl ester (BAEE, TCI Chemicals, Tokyo, Japan) in 50 mM pH 7.6 phosphate buffer. The enzyme trypsin (AMERSCO, Road Solon, OH) was dissolved in the same buffer at a concentration of 7.5 or 25 µM (depending on the flow rate). 10% D₂O was added to the substrate solution for frequency locking. The substrate and enzyme solutions were injected into the mixer device in a 1:1 volume ratio with the use of a syringe pump (Fusion 200 Touch, Chemyx, Stafford, TX). Notice that although in the ensuing sample the enzyme-substrate system may be in equilibrium, the EPSI experiment measures a unidirectional Enzyme+Substrate ⇌ Enzyme-Substrate → Product process that proceeds towards completion as a function of reaction/flow time.

Sample and buffer solutions were injected into the PDMS device with two syringe pumps (Fusion 200 Touch, Chemyx, Stafford, TX, USA) to sustain stable flow rate. The loaded syringes were connected to 1/16′′ Tygon^® tubings (IDEX Health & Science LLC, Oak Harbor, WA, USA) using proper fittings and then secured to the device inlets. The sample and PBS loaded syringes were connected to the outer inlet (I_s) and inner inlet (I_b) of the microchip using Tygon^® tubing, respectively. The two outlets of the microchip were connected to two separation containers via Tygon^® tubings for target cells (CTCs) and waste cells (WBCs). The flow rates for sample and PBS solution were 100 and 200 µL/min respectively.