High aspect ratio induced spontaneous generation of monodisperse picolitre droplets for digital PCR

Abstract

Droplet microfluidics, which involves micrometer-sized emulsion droplets on a microfabricated platform, has been demonstrated as a unique system for many biological and chemical applications. Robust and scalable generation of monodisperse droplets at high throughput is of fundamental importance for droplet microfluidics. Classic designs for droplet generation employ shear fluid dynamics to induce the breakup of droplets in a two-phase flow and the droplet size is sensitive to flow rate fluctuations, often resulting in polydispersity. In this paper, we show spontaneous emulsification by a high aspect ratio (>3.5) rectangular nozzle structure. Due to the confinement and abrupt change of the structure, a Laplace pressure difference is generated between the dispersed and continuous phases, and causes the thread thinning and droplet pinch-off without the need to precisely control external flow conditions. A high-throughput droplet generator was developed by parallelization of a massive number of the basic structures. This device enabled facile and rapid partition of aqueous samples into millions of uniform picolitre droplets in oil. Using this device, on-chip droplet-based digital polymerase chain reaction (PCR) was performed for absolute quantification of rare genes with a wide dynamic range.

Microfluidics and catalyst particles

“…However, chips have been recently developed to parallelize the production of droplets with good monodispersity by minimizing the flow rate variation 182 or by using emulsification processes that do not depend on the flow rate. [183][184][185] With this technology, relatively large quantities of catalysts could be synthesized with optimal control of the reaction conditions, which could be used to synthesise NPs or catalyse reactions in microfluidic reactors.…”

Peanut Detection Using Droplet Microfluidic Polymerase Chain Reaction Device

“…On-Chip PCR. The chip was baked in an oven at 100°C for 8 h to render the PDMS microchannel surface hydrophobic [21]. Subsequently, the Sigmacote surfactant was introduced into the entire microchannel to form a hydrophobic film on the microchannel surface.…”

Scalable Production of Monodisperse Functional Microspheres by Multilayer Parallelization of High Aspect Ratio Microfluidic Channels

“…Our strategy is the parallelization of the droplet generators in a multilayer device for upscaling the production. The basic unit of the droplet generator is a high aspect ratio rectangular nozzle structure, which was previously reported by us to achieve droplet self-emulsification by the confinement and abrupt change of the high aspect ratio geometry of the nozzle and opening to the connection chamber [31]. As the droplet generation is driven by the interfacial tension in this droplet generator, the flow interference is decoupled and the resulting droplet size is solely determined by the width of the nozzle and is not sensitive to flow fluctuations, which enables facile and massive parallelization of such basic units in a single-layer device.…”