the Nobel laureate technology that changed the biology

The Nobel Prize in Physics 2018 was awarded to three pioneers of laser technology that had a tremendous impact on the world. Gérard Mourou and Donna Strickland have been recognized for their method of generating ultra-short and high-intensity optical pulses, currently used in laser eye surgery. The other recipient was Arthur Ashkin for his innovative work on optical tweezers. This method of using light to capture and manipulate tiny objects has changed the way we can study microscopic life.

But how to use light to move the material? The energy conveyed by light is fundamental to life on our planet. But in addition to energy, the light beams also have an impulse, called radiation pressure. This means that if I point a laser pointer at you, in addition to making you a little warmer, it will drive you away with very little force.

Using this force to lift something as big as an apple, for example, would be almost impossible. The required laser power would reach several megawatts, probably enough to vaporize the apple before it takes off. But when an object becomes ten times smaller in each direction, it also becomes 1000 times lighter. So if you go from something the size of an apple to a single cell, the laser power needed to lift it goes from megawatts to milliwatts, a power similar to that of a laser pointer.

As early as 1970, Ashkin (working in world-renowned Bell Telephone Laboratories) began to study how to use radiation pressure to accelerate and trap individual particles. Over the next 15 years, he honed his ideas and brilliantly made the laser systems involved less and less complicated as time went on.

In 1986, working with Steven Chu (who later won his own Nobel Prize in Physics in 1997 for his work on trapping atoms and eventually became US Secretary of Energy), he published his landmark article on what we now call the optical tweezers. In this article, Ashkin showed that if the laser beam was focused very closely using a microscope, instead of repelling objects with radiation pressure, it would counter-intuitively attract particles. . When the laser beam was then moved, the particles followed it, held in the center of the beam at all times.

Since then, many physicists and engineers have used optical tweezers, which have extended the technique to trap multiple particles at once and even turn them into optical keys that rotate objects. The latter area is one of my areas of research and I remember as a young researcher the thrill of Ashkin, who asked me for a copy of my speech at a conference.

Impact in biology

Perhaps the greatest impact of optical tweezers has been in biophysics. Optical tweezers can be used to sort healthy cells from infected cells or to identify those that may be cancerous. It is also possible to use optical tweezers to measure both the minute movements of an object trapped (equivalent to a few atoms in diameter) and the same minute forces.

By transforming optical tweezers from a manipulation tool into a measuring instrument, biologists have been able to study the functioning of the individual molecular motors responsible for movement in the biological world. These engines carry chemicals within molecules, allow cells to swim and, when acting collectively, allow whole creatures to move.

Ashkin showed us all that can be done by having an idea and finalizing it. For years, he worked in a minority field, pioneered and refined his ideas by inventing techniques that scientists now use as essential tools of their profession – thank you Arthur.