Control of individual water droplets as a biochemical reactor

Controlling individual water droplets as a biochemical reactor: Scientists at Ritsumeikan University in Japan are developing ways to better manipulate small water droplets in lab-on-a-chip applications for biochemistry, cell culture and drug screening. ..Credit: Ritsumeikan University, Japan

Miniaturization is rapidly changing the field of biochemistry, with new technologies such as microfluidics and lab-on-a-chip devices dominating the world. Chemical reactions that normally take place in flasks and tubes can now be carried out in small water droplets of a millionth of a liter or less. In the droplet arrangement sandwich technique in particular, such small droplets are neatly arranged on two opposite parallel flat surfaces. By bringing the top surface close enough to the bottom surface, the droplets on each top surface come into contact with the droplets on the opposite bottom surface, exchanging chemicals and even moving particles or cells. Literally, these droplets can act as small reaction chambers or cell cultures, and also serve as liquid processing tools like pipettes, but on a much smaller scale.

The problem with droplet sandwiches is that there is no individual control. Syringes; Once the top surface is lowered, each droplet on the bottom inevitably comes into contact with the droplet on the top. In other words, this technology is limited to batch operations, which limits its versatility and increases its cost. Is there an easy way to select the droplets that will come into contact when the surfaces approach?

Thanks to Professor Satoshi Konishi of Ritsumeikan University and his colleagues, the answer is certainly yes. In a study recently published in Science report, the team of scientists presented a new technology that enables an individual selection of droplets for contact in a droplet array sandwich. The idea behind their approach is pretty simple. If the height of the individual droplets on the ground can be controlled so that some of the stands are higher than the other droplets, then both surfaces are brought closer and only these droplets touch the corresponding droplets. And the rest. It was a little difficult to see how this was actually achieved, however.

Researchers previously used electricity to control the “wetting” of the dielectric in the area under each droplet. This approach, known as “dielectric electrowetting (EWOD)”, can slightly alter the balance of forces that collect water droplets when they are placed on a surface. By applying voltage under the droplet, you can easily disperse the droplet, increase its area, and decrease its height. However, the team found that the process could not be easily reversed because when the voltage was turned off, the droplets did not naturally return to their original height.

To address this problem, they developed EWOD electrodes with a hydrophilic-hydrophobic pattern. When the electrode is switched on, the process described above causes the droplets to spread and shorten on the electrode. Conversely, when the electrode is switched off, the hydrophobic part on the outside of the electrode repels the droplets and the hydrophilic part on the inside attracts the droplets. This will restore the drop to its original shape and height.

Researchers demonstrated their method by placing multiple EWOD electrodes on the underside of the droplet array sandwich platform. Simply apply a voltage across the selected electrodes to select the pair of droplets that will come into contact as the upper platform is lowered. In their demonstration, they transferred the red dye from the top droplets to just a few lower droplets. “Our approach can be used to make individual contacts between droplets electrically, to easily control the concentration of chemicals in these droplets, or to move living cells towards and from one another. You can, ”explains Professor Konishi.

This research paves the way for a potentially fruitful combination of droplet processing technology and automation. “Lab-on-a-Chip technology using droplets is intended to replace traditional manual manipulation with tools such as pipettes and improve the efficiency of drug screening, which will support the drug discovery process. It is accelerated, ”emphasizes Professor Konishi. By cultivating cells in suspended droplets that have been used in cell biology, it also makes cell-based evaluation of drugs and chemicals cheaper and faster, which is valuable in biochemistry and cell biology. He adds that it will be a tool.

We hope that the results of this technology “fall” right there.

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For more informations:
Satoshi Konishi et al., Selective Control of Contact and Transport Between Pairs of Droplets by Dielectric Electrowetting for Droplet Arranging Sandwich Technology, Science Report (2021). DOI: 10.1038 / s41598-021-91219-x

Provided by Ritsumeikan University

Quote: Small tools: https: // Biochemical reactor Received on July 7th, 2021 (July 7th, 2021 control of individual water droplets as day)

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