The versatile control of droplets at various scales offers great promise in multiple domains, especially in precision chemistry and biomedical diagnostics. To effectively manipulate droplets, it’s essential to integrate multifunctional techniques that work across different scales.
Magnetic excitation has become widely accepted in droplet manipulation due to its advantages, including remote control, biocompatibility, insensitivity to substrate charge, and transparency. Nevertheless, enhancing the capabilities of magnetically responsive droplet manipulation and extending functionalities from microliters to nanoliters remain significant challenges.
To address this challenge, Professor Hu Yanlei and his research team at the Micro/Nano Engineering Laboratory at the University of Science and Technology of China (USTC), in collaboration with other researchers, have developed a magnetically actuated Janus origami robot using femtosecond laser nanofabrication techniques. This robot seamlessly integrates various droplet manipulation functions, including three-dimensional transport, merging, splitting, precise dispensing, on-demand release of daughter droplets, stirring, and remote heating.
This manipulation strategy exhibits remarkable stability and allows manipulation of droplets ranging from approximately 3.2 nanoliters to about 51.14 microliters. The research, titled “Magnetic Janus origami robot for cross-scale droplet omni-manipulation,” has been published in Nature Communications.
The Janus origami robot has distinct wetting properties on its upper and lower surfaces. The upper surface is superhydrophobic with low droplet adhesion, while the lower surface is hydrophobic with high droplet adhesion. Two creases on the upper surface facilitate droplet envelopment through capillary forces upon contact. The robot’s overall profile and surface micro/nano-functional structures are fabricated and modified using femtosecond laser scanning.
Under the influence of a magnetic field, the robot actively approaches and encapsulates water droplets by rolling, enabling controlled droplet transportation. Additionally, it can distribute daughter droplets from larger droplets through directed rolling and folding.
By adjusting the magnetic field strength, the robot can extrude the distributed daughter droplets. Its superhydrophobic exterior allows gentle pushing for controlled release and separation. The robot can also rotate under the magnetic field’s influence, facilitating controlled liquid mixing and, in combination with its photothermal properties, enabling remote heating.
These magnetic-responsive Janus origami robots offer versatile cross-scale droplet manipulation, resembling commercial magnetic stirrers. They excel not only in rapidly mixing water but also effectively mixing high-viscosity liquids like glycerol, achieving temperatures exceeding 80°C through their heating and stirring functions.
These robots autonomously approach water droplets through rolling, dispense specific volumes of daughter droplets, transport and merge these daughter droplets with others, and facilitate rapid mixing of different-component droplets through stirring. This multifunctional droplet manipulation extends seamlessly to the nanoliter scale.
In a proof-of-concept demonstration, the robots, with surface modifications, successfully extracted and purified nucleic acids.
In summary, magnetic-responsive Janus origami robots revolutionize cross-scale droplet manipulation, with profound implications for precise reagent delivery, microdroplet patterning, and rapid microdroplet reactions in various fields, including fine chemical engineering, medical diagnostics, and microfluidic technologies.