Abstract
A microfluidic droplet-storage array that is capable of the continuous operation of droplet formation, storing, repositioning, retrieving, injecting and restoring is demonstrated. The microfluidic chip comprised four valve-assisted droplet generators and a 3 × 16 droplet-storage array. The integrated pneumatically actuated microvalves enable the precise control of aqueous phase dispensing, as well as carrier fluid flow path and direction for flexible manipulating water-in-oil droplets in the chip. The size of droplets formed by the valve-assisted droplet generators was validated under various operating conditions such as pressures for introducing solutions and dispensing time. In addition, flexible droplet addressing in the storage array was demonstrated by storing droplets with various numbers and compositions in different storage units as well as rearranging their stored positions. Moreover, serial injections of new droplets into a retrieved droplet from a storage unit was performed to show the potential of the platform in sequential dosing on incubated droplet-based reactors at the desired timeline. The droplet-storage array with great freedom and flexibility in droplet handling could be applied for performing complex chemical and biologic reactions, especially in which incubation and dosing steps are necessary.
Highlights
Droplet-based microfluidic systems that manipulate nano- or picoliter droplets in microchannels have been highlighted in high-throughput chemical and biologic screening with rapid and robust reactions [1,2,3,4]
A pneumatically actuated microfluidic valve [31] was placed at the T-junction of an aqueous and the carrier fluid channels to control the connection between the two flows
All the droplet handling processes were performed by automated microfluidic valve control
Summary
Droplet-based microfluidic systems that manipulate nano- or picoliter droplets in microchannels have been highlighted in high-throughput chemical and biologic screening with rapid and robust reactions [1,2,3,4]. One of the fundamental aspects of the droplet-based systems for analytical chemistry and biology is preparing libraries of samples in various compositions as well as concentrations. For varying the combination and concentration of reagents in a series of droplets, microfluidic mixers were integrated with droplet generators [5,10,11]. Several flowing streams were emerged into a microfluidic mixer and flowed into a carrier fluid flow to form droplets with various conditions. The other concept to create concentration gradients along droplets is merging droplets by synchronizing droplets in a microchannel network [22] or using hydrodynamics with microstructures designed to trap and release droplets [13,14,23,24]
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