Enzyme kinetic measurements using a droplet-based microfluidic system with a concentration gradient

In this Paper We propose a microfluidic device that is capable Of generating a concentration gradient followed by parallel droplet formation within channels with a simple T-junction geometry. Linear concentration gradient profiles can be obtained based on fluid diffusion under laminar flow. Optimized conditions for generating a linear concentration gradient and parallel droplet formation were investigated using fluorescent dye. The concentration gradient profile under diffusive Mixing was dominated by the flow rate at sample inlets, while parallel droplet formation was affected by the channel geometry at both the inlet and outlet The microfluidic device was experimentally characterized using optimal layout and operating conditions,selected through a design process. Furthermore, in situ enzyme kinetic measurements of the beta- galactosidase-catalyzed hydrolysis of resorufin-beta-D-galactopyranoside were,performed to demonstrate the application potential of our Simple, time-effective, and low sample volume microfluidic device. We expect that, in addition to enzyme kinetics, drug screening and clinical diagnostic tests can be rapidly and accurately performed using this droplet-based microfluidic system.This study was supported by National Research Foundation (NRF) grants funded by the Korean government (MEST) (Grant No. 2010-0024293 and Grant No. R11-2008-044-01003-0). We also acknowledge the financial support of the Ministry of Knowledge Economy (MKE) and the Korea Industrial Technology Foundation (KOTEF) through the Human Resources Training Project for Strategic Technology