A multiplexable microfluidic injector for versatile droplet identification

This research summary describes the research paper “A Multiplexable Microfluidic Injector for Versatile Encoding of Droplets” by Johnson Q. Cui, Binbin Cui, Frank X. Liu, Yuan Lin, and Shuhuai Yao.

The study exploits pressure-controlled injection to achieve deterministic droplet coding for droplet identification and tracking.

ABSTRACT

Microfluidics’ high throughput, precision, and cost-effectiveness make it ideal for droplet synthesis. Droplet identification and tracking, however, is still a challenge. Shuhuai Yao and colleagues describe a multiplexable injector with a distinctive design. Their system comprises a circular electrode and concentric fluidic channel accommodating multiple injection ports for on-demand droplet injection and encoding. The scientists used pressure pulse regulation to precisely inject droplet ingredients and a colour-coded system to further identify droplets via an image analysis algorithm. The platform created is quite versatile, compact, easy to integrate and can potentially be used in applications where multiplexing compound screening, combinatorial synthesis, or other multistep assays are required.

INTRODUCTION | Droplet identification and tracking

The colossal number of droplets required makes droplet identification and tracking a challenging task, hindering their application as individual bioreactors. Previous droplet coding schemes suffer from drawbacks such as large footprints, the requirement of specially designed chips, or complicated dispensing modules [1][2].

Herein, the researchers developed a multiplexable injector which exploits a distinctive design comprising a circular electrode and a concentric fluidic channel to accommodate multiple injection ports for on-demand droplet injection and encoding. Different droplet coding schemes are demonstrated for droplet identification and tracking.

AIMS

• Developing a multiplexable picoinjector with a controlled injection ability
• Achieving on-demand injection by controlling pressure
• Developing facile and robust droplet coding schemes for droplet tracking and identification

EXPERIMENT SETUP | Precise volume injection and pressure control

Droplet emulsions and oil phase are introduced into the device by a syringe pump. The injection is activated via interfacial coalescence by the applied electric field [3]. 

By using the Elveflow OB1, the injection volume can be precisely controlled by the pressure applied to the injection channel. The photograph and the schematic drawing of the device are shown in Fig 1.

MATERIALS

• OB1 flow controller
• HFE-7500 (3M) with 1% surfactant (RAN Biotechnologies)
• Syringe pump (PHD ULTRA^TM, Harvard Apparatus)
• Fluorescein (FITC) or food dyes (added to the injection fluid as barcodes)
• Eclipse Ti2, Nikon inverted microscope 
• ANDOR, Oxford Instruments sCMOS camera 
• DS-Fi3, Nikon colour camera

KEY FINDINGS | Versatile droplet identification and tracking

• A multiplexable injector is configured as a concentric design of a fluidic channel and a circular electrode in a small footprint.
• Droplets can be deterministically injected with any patterns by using a programmable pressure source (OB1 flow controller), which can be further decoded and tracked downstream. The injected volume can be precisely controlled by the injection pressure (Fig 2).
• Multiple barcodes can be dosed into droplets for versatile droplet identification, tracking, and multistep bioassays (Fig 3).

CONCLUSION | A platform for droplet injection, encoding, and tracking

We developed a versatile and multiplexable injector platform for droplet injection, encoding, and tracking. 

We achieved on-demand injection by simply employing a programmable pressure pulse such that droplets can be injected at any self-defined patterns corresponding to the applied pressure regulation. 

We further integrated three injectors in a single device, all of which can be controlled individually to perform the on-demand injection of multiple targets or barcodes, thus various colour barcoding schemes are demonstrated. 

References