Single-molecule enzymatic analysis in a droplet-based microfluidic system

The kinetic activity of individual enzyme molecules was determined in aqueous droplets generated in a nano- and microfluidic device. To avoid high background noise, the enzyme and substrate solution was confined into femtolitre carriers to achieve single-molecule encapsulation. The tiny droplets (f~2.5-3 μm) generated from this fluidic system were highly monodisperse, beneficial for an analysis of single enzyme activity. Single-enzyme kinetics has previously been demonstrated in the microfluidic format in PDMS containers [1], surface-immobilized droplets [2], or liposomes [3]. Single- enzyme analysis in the droplet-based microfluidics was reported before [4] by encapsulating highly-diluted enzyme solution (110 fM) into large droplets (f~40 μm). But to our knowledge this is the first demonstration of the direct method of single enzyme encapsulation and analysis at high enzyme concentration in tiny droplets in a microfluidic system

Electrochemical analysis of microdroplet formation

This paper reports an electrochemical measurement system with a high-speed camera for observation of molecular transport phenomena at a water-oil (W/O) interface during microfluidic droplet formation. For demonstration of the system, currents corresponding to the transport of electrolyte ions to form the electrical double layer at the liquid interface were measured. Additionally, the high-speed camera observation revealed charge-effect on droplet stability during and/or just after the formation. This measurement system is expected to facilitate a full understanding of the droplet formation process

Microfluidic pump based on arrays of rotating magnetic microspheres

We demonstrate a novel, flexible and biocompatible method to pump liquid through microchannels without the use of an external pump. The pumping principle is based on the rotation of superparamagnetic microspheres around permalloy disks, driven by an external in-plane rotating magnetic field. By placing the permalloy disks close to the edge of the channel, a net flow of 9 μm/s was generated in the middle of the channel. This pumping principle is especially suited for flow controlled medium recirculation in culture chambers, opening ways towards portable, on-chip closed cell culturing [1]