Measuring rapid enzymatic kinetics by electrochemical method in droplet-based microfluidic devices with pneumatic valves.

This paper describes a droplet-based microfluidic chip with pneumatic valves for measuring millisecond enzyme kinetics using amperometric detection method. Aqueous streams containing reactants were injected to an oil flow to form droplets, and each droplet represented one microreactor. Pneumatic valves were used to control the moving distance and in turn the reaction time of the droplets. The reaction time was also fine-tuned by varying the flow rate of the droplets in microchannels. A complete Michaelis-Menten kinetics of catalase was successfully measured by amperometric method in a single-run experiment, and the total consumption of reagents was less than 50 microL. In the current experiment, the best time resolution was about 0.05 s, and the reaction time measured was from 0.05 to 25 s. This microfluidic system is applicable to many biochemical reactions, as long as one of the reactants or products is electrochemically active. With appropriate quenching method at the outlet, various detection methods can be integrated into the microfluidic system, further extending the application of the combination of pneumatic valves and droplets in microchannels.