The diverse manipulation of droplets across scales has important application prospects in the fields of fine chemistry and biomedical detection. From a practical point of view, effective droplet manipulation technology requires multi-functional integration and multi-scale applicability. In recent years, magnetic excitation has been widely used in the field of droplet manipulation due to its advantages of remote control, good biosecurity, and insensitivity to environmental transmittance and base charge. However, how to further expand the function of magnetic response droplet manipulation and expand the diversified droplet manipulation from microliter scale to nanoliter scale remains a challenge. In view of this, the team of Professor Hu Yanlei and his collaborators in the Laboratory of Micro and Nano Engineering at the College of Engineering Science at the University of Science and Technology of China (USTC) have used femtosecond laser micro-nano fabrication method to prepare a magnetically responsive Double-face origami robot that can be used for cross-scale droplet manipulation, and effectively integrate diverse droplet manipulation functions. It includes droplet three-dimensional transport, merging, splitting, droplet distribution and on-demand release, stirring and remote heating. At the same time, the high stability of this control strategy gives it the ability to manipulate droplets across scales, which can be controlled in the volume range of ~3.2 nL to ~51.14 μL. The work was published September 6 in Nature Communications under the title "Magnetic Janus origami robot for cross-scale droplet omni-manipulation."
Figure 1. Magnetic response Janus Origami robot and its multifunctional droplet manipulation application
The upper and lower surfaces of the magnetic response Janus origami robot have different wetting characteristics respectively. As shown in Figure 1, the upper surface of the robot is in a state of super-hydrophobic low droplet adhesion, while the lower surface is in a state of hydrophobic high droplet adhesion. At the same time, the upper surface of the robot is also designed with two creases, so that when the robot is in contact with the droplet, it can spontaneously wrap the droplet under the action of capillary force. The machining and modification of the robot's overall contour, crease and surface micro/nano functional structure are all made by second laser scanning. Driven by magnetic field, the robot can actively approach and wrap the water droplets by rolling, which can realize the controllable transport of water droplets. In addition, the magnetically responsive Janus origami robot can also distribute child droplets from large droplets by directional tumbling and folding. The distributed droplet can be squeezed out of the robot by controlling the strength of the magnetic field. Using its specially designed superhydrophobic outer surface, the robot nudges the water droplets to achieve controlled release separation of the daughter droplets. The robot can also rotate under the action of a magnetic field to achieve a controlled mixing of liquids and, combined with its photothermal properties, remote heating.
Figure 2. Droplet agitation, photothermal agitation and multifunctional droplet manipulation integration based on magnetic response Janus origami robot
As mentioned earlier, the magnetic response Janus origami robot can achieve mixing and heating functions similar to commercial magnetic mixers. The fluorescence distribution diagram in Figure 2 clearly shows the mixing degree of the droplets during the stirring process. In addition to the rapid mixing of water, the hot stirring function of the robot can also effectively achieve the rapid mixing of high-viscosity liquids (glycerin). The heating temperature can reach more than 80℃.
On the basis of diversified droplet manipulation, the magnetic response Janus origami robot can effectively integrate various droplet manipulation functions to achieve continuous droplet manipulation goals. For example, the robot can actively approach the water drop through tumbling motion and distribute a certain volume of child droplets, combine the distributed child droplets with another droplet through directional transport, and finally achieve rapid mixing of droplets with different components by stirring. This multifunctional droplet manipulation integration can also be effectively extended to nanoscale droplets.
Finally, as a proof of concept, nucleic acid extraction and purification was successfully achieved by surface modification of the magnetically responsive Two-face origami robot combined with its diverse droplet manipulation functions (Figure 3). In summary, the magnetic response Two-face origami robot can achieve cross-scale droplet manipulation, which is of great significance for the wide range of fields such as fine chemical industry, medical diagnosis and microfluidics technology requiring the acquisition and addition of reagents, microdroplet pattern and rapid microdroplet reaction.
Figure 3. Application of nucleic acid extraction and purification based on magnetic response Two-face origami robot
Dr. Jiang Shaojun from the School of Engineering Science is the first author of the paper. Corresponding authors are Prof. Yanlei Hu and Dong Wu, University of Science and Technology of China, and Prof. Liqiu Wang, Hong Kong Polytechnic University. Co-authors of the paper include Professor Chu Jiaru and Associate Professor Li Jiawen from the University of Science and Technology of China, Researcher Zhu Ling from the Anhui Institute of Optics and Fine Mechanics, Hefei Institute of Physical Sciences, Chinese Academy of Sciences, and Professor Shen Zuojun from the First Affiliated Hospital of the University of Science and Technology of China. This research work has been supported by the National Natural Science Foundation for Excellent Young Scientists, the Youth Innovation Promotion Association of the Chinese Academy of Sciences, and the National Key Research and Development Program of the Ministry of Science and Technology.
(School of Engineering Science, Department of Scientific Research)
Source: China University of Science and Technology News
