Complex Emulsions as Real-Time Flow Sensor
The National Dong Hwa University is renowned for its interdisciplinary research across various scientific fields, with a strong experimental focus on developing new materials and methods for sensing technologies. This case study highlights Rakesh et al.’s successful application of complex emulsions to advance real-time flow sensing technology.[1]
A National Dong Hwa University Study
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“Our experience using the LineUp Flow EZTM pressure pump with the RayDrop chip has been positive. The pump’s high precision and accuracy have allowed us to achieve consistent and reproducible results in our microfluidic experiments. Additionally, the pump’s compact size and user-friendly interface have made integrating into our existing setup easy. The combination of Fluigent’s LineUp Flow EZTM pressure pump and RayDrop chip has great potential for advancing microfluidic research, and we are excited to continue exploring their capabilities in our ongoing studies.“
Che-Jen Lin, Ph.D., Assistant Professor at National Dong Hwa University. Organic Chemistry
Introduction
This case study examines a specific application of complex emulsions. With Secoya’s Raydrop and Fluigent’s Flow EZTM flow control technology, researchers Rakesh et al. of the National Dong Hwa University precisely generated and controlled complex liquid emulsions to use them as a real-time iodine concentration flow sensor. This research opens a way to explore new applications in environmental monitoring, industrial process optimization and medical substance detection.
Why generate complex emulsions?
Emulsions are microscale spheroid structures formed by blending two immiscible liquids (often an oil phase and an aqueous phase). What differentiates complex emulsions (figure 1b) from simple emulsions (figure 1a) is their multi-layered structure. Within a complex emulsion, micro droplets of one liquid are intricately dispersed within another, forming a heterogeneous droplet with exceptional properties. When properly generated and stabilized, complex droplets can be used to encapsulate active or reactive compounds, such as Active Pharmaceutical Ingredients,[2] or to design innovative functional particles. [3]
Some complex droplets can adopt temporary Janus configurations. Janus droplets have two distinct faces (figure 1c), each featuring unique properties achieved through selective surface modifications.[4] Their surface properties dynamically adjust over time or in response to external stimuli.
Generating complex droplets
Emulsion Setup
In this study, complex emulsions were generated with a mixture of hydrocarbon oil (heptane) and fluorocarbon oil (FC-770). To ensure a homogeneous solution, the mixture of heptane and FC-770 was heated above the upper critical temperature (50°C). 4×10-7 mmol of CNFCPEG was dissolved in 500µL of heptane and 500µL of FC-770.
To generate complex emulsifications, the researchers employed Secoya’s single emulsion Raydrop coupled with Fluigent’s Flow EZTM flow controller to facilitate the creation of highly monodispersed droplets. Through this setup, they achieved precise control over pressures and flow rates, leading to the generation of controlled monodisperse droplets in the 50 to 80 µm range.
Raydrop Double Emulsion
Alternatively, an easier way to produce double emulsions is by using the new double emulsion Raydrop developed by Secoya. Thanks to its double nozzles, this new Raydrop can generate double emulsions in one step, creating a core-shell structure. The size of the core and shell can be precisely controlled, offering versatility in applications such as drug delivery systems.
Using complex emulsions to measure iodine concentration
The key role of CNFCPEG
In this study, CNFCPEG, an innovative compound, plays a major role in stabilizing complex emulsions without the need for external surfactants. CNFCPEG also exhibits two fluorescence colors (blue and green) depending on its aggregation state. When CNFCPEG aggregates in an organic phase, a blue color is observed, while the green excimer is observed when CNFCPEG self-assembles at the fluorinated oil/water interface (F/W). By evaluating fluorescence emissions, the distinction between H/F/W and F/H/W emulsions becomes clear and easily distinguishable.
Heptane-FC 770-CNFCPEG complex emulsion in DI water presents the H/F/W morphology. Addition of iodine to the DI water reduces the hydrophilicity of CNFCPEG’s PEG group, leading to an instantaneous morphology shift from H/F/W to Janus to F/H/W complex emulsion. This morphological shift, combined with the fluorescent color change, makes it possible to to detect the presence of iodine in water.
Complex droplets as iodine real-time sensing platform
To enhance the precision and accuracy of data acquisition in real-time flow sensing, the researchers designed a Multiple-well Flow PDMS Chip (MWFC) that allows for parallel tracking of multiple droplets (figure 6). This innovative chip facilitates the monitoring of droplet behavior, morphological changes, and interactions within complex droplets.
Iodine was injected into the MWFC, inducing a decrease in the hydrophobic nature of the CNFCPEG and initiating an instantaneous morphological change in the stabilized complex droplets (figure 7b, figure 8). The droplets transitioned from H/F/W to Janus more quickly with increasing iodine concentration. Slower flow rates corresponded to longer transition times, providing quantitative insights into analytes (figure 7c).
Conclusion
Rakesh et al.[1] from National Dong Hwa University demonstrated the potential of complex emulsions as a precise and affordable real-time flow sensor, opening the way for many potential applications. Secoya’s technology and Fluigent’s technology allowed for generation and precise manipulation of the complex droplets used in this study. This case study shows the versatility and simplicity of our instruments. It also demonstrates Fluigent’s commitment to driving innovation in a variety of scientific domains, making microfluid handling and analysis more accessible for researchers worldwide.
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References
[1]Rakesh, N., Tu, H.-L., Chang, P.-C., Gebreyesus, S. T., Lin, C.-J., Innovative Real-Time Flow Sensor Using Detergent-Free Complex Emulsions with Dual-Emissive Semi-Perfluoroalkyl Substituted Α-Cyanostilbene. Adv. Sci. 2023, 2304108. https://doi.org/10.1002/advs.202304108
[2]Linghao Qin, Yawei Niu, Yuemin Wang, and Xiaomei Chen, Molecular Pharmaceutics 2018 15 (3), 1238-1247, DOI: 10.1021/acs.molpharmaceut.7b01061
[3]Justin R. Finn, Janine E. Galvin, Modeling and simulation of CO2 capture using semipermeable elastic microcapsules, International Journal of Greenhouse Gas Control, Volume 74, 2018, Pages 191-205, ISSN 1750-5836, https://doi.org/10.1016/j.ijggc.2018.04.022. [4]Bradley D. Frank, Markus Antonietti, and Lukas Zeininger, Macromolecules 2021 54 (2), 981-987, DOI: 10.1021/acs.macromol.0c02152