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NTHU Researchers Discover a Ground-breaking Molecular Switch
A micro-machine injected into the human body to repair damaged organs may sound like something straight out of a science fiction, but before long it may well come true. A research team led by Prof. Masaki Horie of the Department of Chemical Engineering and doctoral student Kai-Jen Chen have succeeded in creating a light-controlled molecular switch as slender as a single hair, yet conveying energy equal to more than 1,650 times its own weight. With Chen serving as the first author, their research report has recently been published in the prestigious journal Nature Communications.
 
This year's Nobel Prize in Chemistry was awarded to three distinguished scientists working in the field of molecular machines, highlighting the importance of this research area. In the report Chen says that a molecular machine is a tiny device controlled by such external stimuli as light, heat, and electrical signals to produce movements at the molecular scale similar to those of motors, gears, and muscles.
 
Under Horie’s guidance, Chen conducted a series of experiments with solid-body single crystals, which have wider applications than those conducted in a liquid, but are also more challenging. He found that ferrocene supramolecular crystals expand when illuminated by blue laser irradiation, and that they quickly return to their original state once the irradiation is removed. Imbedded into an electrical circuit, these expansions and contractions become a photo-induced supramolecular switch.
 
It was also found that this photo-induced supramolecular switch can be switched on and off ten times per second, which amounts to 600 times per minute, while still maintaining a fairly stable current. According to Chen, "In the future, it may well be possible to accelerate the speed of such a switch to 85 times per second!"
 
Using this tiny super-fast molecular switch to remotely control material objects, the research team uses a micro-sensing system to discover that, by converting optical energy into mechanical kinetic energy, a supramolecular crystal can flip globules 1,650 times heavier than its own weight.
 
Since the experiments entailed positioning supramolecular crystals only a few dozen micrometers in size—smaller than the average mote of dust—on the tip of a needle, the slightest draft could have a confounding effect. Thus Chen conducted the experiments in the dead of night, with the laboratory air-conditioning turned off, peering into the microscope while holding his breath. Looking back on the meticulous conditions, he joked, “Now I’m able to easily hold my breath for up to a minute without any discomfort."
 
Wary of biting off more than they can chew, many graduate students select a “safe” research topic they are sure can be completed in a short time. By contrast, encouraged by Prof. Horie, Chen chose the highly challenging research topic of photoresponsive supramolecules, which he worked on for four years. Yet, with the continual expert guidance and support of his mentor, Chen obtained outstanding results and his research report—his very first—has been published in an internationally renowned journal.
 
Horie says that their discovery of the photo-induced supramolecular switch was something of an accident. Thus he always encourages students to try things out and play around a bit, since “You never know what you might discover.” Horie has been teaching at NTHU since 2010, and has been highly impressed with the university’s facilities and research environment.
 
The photo-induced supramolecular switch is an area of basic research with the potential to rewrite the history of science and technology. Horie expects that it will soon be possible to develop molecular machines which are smaller, more complex, and more functional. Once they are advanced enough to function like a tiny computer, they can be injected into the body d to repair damaged organs.
 
The groundbreaking discovery of a molecular switch by Associate Prof. Masaki Horie (right) and doctoral student Kaj-Jen Chen (left) has recently been published in Nature Communications.

The groundbreaking discovery of a molecular switch by Associate Prof. Masaki Horie (right) and doctoral student Kaj-Jen Chen (left) has recently been published in Nature Communications.

The groundbreaking discovery of a molecular switch by Associate Prof. Masaki Horie (right) and doctoral student Kaj-Jen Chen (left) has recently been published in Nature Communications.

The groundbreaking discovery of a molecular switch by Associate Prof. Masaki Horie (right) and doctoral student Kaj-Jen Chen (left) has recently been published in Nature Communications.

Left: Irradiated by laser light, the molecular crystal instantaneously expands, causing the globule to bounce.
Right: Controlling the laser light to adjust the crystal’s rate of expansion and shrinkage, the electrical circuit can switch on and off up to 10 times per second.

Left: Irradiated by laser light, the molecular crystal instantaneously expands, causing the globule to bounce. Right: Controlling the laser light to adjust the crystal’s rate of expansion and shrinkage, the electrical circuit can switch on and off up to 10 times per second.

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