Our goal is to build the unprecedented Biomolecular Rocket that achieves the following system functions.
Speeding-up is always on demand. In DNA nanotechnology, some synthetic molecular motors, such as a DNA spider, were proposed to execute nano- to micro-meter scale tasks including molecular tranportation. However, the speed of their movement is slow, compared to a kinesin that is one of the fastest natural molecular motor. Therefore, we decided to challenge the construction of a moleculer vehicle, that can exceed the speed of the kinesin.
Among the vehicles that human beings have so far constructed, a rocket is the fastest one. In addition, a rocket can freely travel across the universe. So, we set our goal to construct a high-speed and remotely controllable molecular vehicle that does not require any rail system, limiting its travelling route.
The Biomolecular Rocket consists of a micrometer-sized bead as its body, submicrometer-sized beads or nanometer-sized catalases as its catalytic engines, and DNA as its steering gear. The rail-free movement is accomplished by taking advantage of bubble propulsion like jet engines. To realize the high-speed movement of our rocket, we conjugated numerous catalytic engines by utilizing sequence-specific DNA hybridization. As a consquence, the directional control of our rocket movement is acheived by triggering region-specific DNA denaturation. As a proof of concept, we constructed a simple version of the Bimomolecular Rocket, as described below.
1. Power supply for the rail-free movement
Biomolecular Rocket moves straightforward by emitting bubbles.
We utilized the submicrometer-sized platinum beads or nanometer-sized catalases that catalyze decomposition of H2O2 into H2O and O2. The generated O2 gas forms a bubble. The dissolved O2 gas surrounding a bubble continues to diffuse into the bubble, causing it to grow while the buoyancy force and surface adhesion compete against one another. When the O2 bubble is emitted from the surface of platinum beads, the accompanying momentum change induces a driving force to put the bubble away from the surface. Therefore, by placing the catalytic engines on the back of the rocket body, the Biomolecular Rocket moves straightforward to the opposite direction, and thus, the rail-free movement is accomplished.
2. Increasing driving force for the high-speed movement
| Biomolecular Rocket gets stronger driving force by increasing catalytic surface area.|
Since the driving force generated upon emission of bubbles depends on the surface area of catalyst, it is expected to speed our rocket up by increasing the surface area of platinum beads and enable it to emit more bubbles. For setting a high-speed record of the Biomolecular Rocket, we attached numerous catalytic engines to a micrometer-sized rocket body, instead of the conventional strategy to use a hemisphere of a bead as a rocket body for the catalytic suface. According to our strategy, the total surface area of the catalytic engines of our rocket is estimated approximately 3.6 times larger than that of a bead hemisphere.
3. Introduction of a photo-switchable DNA system for the directional control
| Direction of the rail-free movement of our rocket can be changed by the UV light irradiation.|
Hybridization and dissociation between a photo-responsive DNA and its complement can be switched upon UV light irradiation. By introducing this photo-switchable DNA hybridzation system into the Biomolecular Rocket, detachment of the catalytic engines can be triggered by UV light. In addition, when the photo-switchable DNA hybridzation system is introduced only at specific regions, the direction of the driving force is also changed upon the photo-triggered detachment of the catalytic engines. Therefore, we can remotely control the direction of the rail-free movement of our Biomolecular Rocket by irradiating UV light.