Capillary-based Centrifugal Microfluidic Device for Size-controllable Formation of Monodisperse Microdroplets

Summary

Here, we demonstrate a simple production method for size-controllable, monodisperse, water-in-oil (W/O) microdroplets using a capillary-based centrifugal microfluidic device. This method requires only a small sample volume and enables high-yield production. We expect this method will be useful for rapid biochemical and cellular analyses.

Abstract

Here, we demonstrate a simple method for the rapid production of size-controllable, monodisperse, W/O microdroplets using a capillary-based centrifugal microfluidic device. W/O microdroplets have recently been used in powerful methods that enable miniaturized chemical experiments. Therefore, developing a versatile method to yield monodisperse W/O microdroplets is needed. We have developed a method for generating monodisperse W/O microdroplets based on a capillary-based centrifugal axisymmetric co-flowing microfluidic device. We succeeded in controlling the size of microdroplets by adjusting the capillary orifice. Our method requires equipment that is easier-to-use than with other microfluidic techniques, requires only a small volume (0.1-1 µl) of sample solution for encapsulation, and enables the production of hundreds of thousands number of W/O microdroplets per second. We expect this method will assist biological studies that require precious biological samples by conserving the volume of the samples for rapid quantitative analysis biochemical and biological studies.

Introduction

W/O microdroplets^1-5 have many important applications for the study of biochemistry and bioengineering, including protein synthesis⁶, protein crystallization⁷, emulsion PCR^8,9, cell encapsulation¹⁰, and construction of artificial cell-like systems^5,6. To produce W/O microdroplets for these applications, important criteria are control of size and monodispersibility of the W/O microdroplets. Microfluidic devices for making monodisperse, size-controllable W/O microdroplets¹¹ are based on the co-flowing method^12,13, flow-focusing method^14,15, and the T-junction method^16....

Protocol

1. Fabrication of a Capillary-based Microfluidic Device

1. Set up of the holders
   Note: The holder design is presented in Figure 2A.
   1. Cut out each of the four discs of the holders (Figure 2A(i)-(iv)) from 2-mm-thick polyacetal plastic plate using a milling machine. Use the following dimensions for each of the four discs of the holder: (i) disc 1 diameter 8.5 mm, capillary hole (CH) diameter 1.3 mm, screw hole (SH) diameter 1.8 mm; (ii) disc 2 diameter 8.7 mm, CH diameter 2.0 mm, SH diameter 1.8 mm; (iii) disc 3 diameter 8.7 mm, CH diameter 0.5 mm, SH diameter 1.8 mm; and (iv) disc 4 diameter ....

Results

In this study, we present a simple method for the generation of cell-sized W/O microdroplets by using a capillary-based centrifugal microfluidic device (Figure 1). The microfluidic device was composed of a capillary holder (Figure 2B), two glass capillaries (inner and outer glass capillaries in Figure 3C), and a microtube containing an oil including surfactant. We injected 0.1 µl of sample solution into the inner glass capillary and place.......

Discussion

Using this device, the monodisperse W/O microdroplets were generated by Plateau-Rayleigh instability of a jet-flow¹⁷. Microscopic examination did not reveal the presence of satellite droplets. In the fabrication of the device, three critical steps are essential to successfully generate monodisperse W/O microdroplets. First, to supply a straight flow of oil containing surfactant and aqueous solution, the capillary holes of four discs must be arranged in a concentric pattern. Second, the inner capillary was care.......

Materials

List of materials used in this article

Name	Company	Catalog Number	Comments
2-mm-thick polyacetal plastic plate	Tool	Nikkyo Technos, Co., Ltd. (Japan)	244-6432-08
Milling machine	Tool	Roland DG Co., Ltd. (Japan)	MDX-40A
End Mill RSE230-0.5*2.5	Tool	NS Tool Co., Ltd. (Japan)	01-00644-00501
M2*40 screws	Tool	Jujo Synthetic Chemistry Labo. (Japan)	0001-024
Glass Capillry Puller	Tool	Narishige (Japan)	PC-10
Microforge	Tool	Narishige (Japan)	MF-900
Inner Glass Capillary	Tool	Narishige (Japan)	G-1
Outer Glass Capillary	Tool	World Precision Instruments Inc. (USA)	1B200-6
1.5 ml Sample tube	Tool	INA OPTIKA CO.,LTD (Japan)	ST-0150F
Hexadecane	Reagent	Wako Pure Chemical Industries Ltd. (Japan)	080-03685
Sorbitan monooleate (Span 80)	Reagent	Tokyo Chemical Industry Co., Ltd. (Japan)	S0060
Milli Q system	Reagent	Merck Millipore Corporation (Germany)	ZRQSVP030
Swinging-out-type Mini-centrifuge	Tool	Hitech Co., Ltd. (Japan)	ATT101
Digital Microscope	Tool	KEYENCE Corporation (Japan)	VHX-2001