Using Light as Tweezers to Move Nanoparticles

We never just stop and think about how important light is in our everyday lives, it’s taken for granted and a bit under-appreciated in my opinion. Just try to imagine a world without light…sounds extremely dull (pun intended).

We wouldn’t be able to see colours, see stars in the sky or or stay up till 3 am reading a book (guilty of this many times):sweat_smile:.

I wouldn’t even be able to write this article without having light illuminate the graphic interface on my computer screen.

The sense of seeing wouldn’t exist without light traveling about 300 000 000 m/s and providing us real-time data about our environment that is reflected in our eyes then interpreted by the occipital lobe in the back of our brains. We would have 4 senses instead of 5! It makes me wonder what a 6th sense could allow us to understand about existence and matter in the universe. What higher version of reality are we unable to ever conceive of without a sense to measure it? Okayyyy I’ll stop here before I turn this into a science fiction book, but you get the point. Life would suck without light.

There is another concept that I want to convey, the importance of focus. Our brains are constantly being bombarded by information every millisecond, it’s surprising how we can even manage to navigate life in such a complex environment. Evolution is definitely to thank for that, but light is constantly entering our eyes and we need to be able to focus the input load to definitively see objects clearly.

Euclid (famous mathematician) pondered about human vision and hypothesized that our eyes sent out focused rays of light onto external objects which were reflected back into our eyes to allow for human sight. He was close, turns out our eyes don’t have superman laser vision but light can be compartmentalized into focused rays that enter our eye and be understood by our brain.

So being able to focus light is an important skill needed to see the world around us. The idea of light being packaged into focused lasers is vital in understanding the idea of optical tweezers, lasers are the essence of this article.

So what do you need to remember?

  • light is extremely important and has allowed us the sense of sight.
  • lasers are an important system of light that help us focus our vision.

Eyesight has hard limitations on the scope of our vision.

Our eyes no matter how great they are, will always be limited to size and distance of the objects it can see. We cannot see far into outer space without a telescope nor can we see nanoscale objects without a microscope.

This means that in these specific environments we cannot use the sense of sight to collect data and understand the complex system. Without technology we would have remained blind to whole ecosystems of the microscopic world. This is crazy because on our bodies alone we host over 100 trillion microbes which is more than or about the same number of human cells.

Without the capability of understanding through observation it’s extremely hard to conceptualize the role of the micro-biome in our bodies and how bacterias aid/harm our health. So many chronic diseases now stem from the micro-biome in our gut and the foods we eat but without the aid of technology we can never truly understand the role they play.

That’s why optical tweezers will allows us to understand nanoscale objects using lasers.

Our everyday life is very strongly affected by the nanoscale world that’s out of reach from our basic senses. Using optical tweezers we can leverage the technology to understand biology of the microscopic life living everywhere around us.

It will allow us to give a deeper depth of vision and also tactile ability to study and manipulate small particles.

What can optical tweezers do?

  • trap small particles and hold them using lasers.
  • move nanoscale objects by exerting a force with lasers.

“What is the fundamental question of cell biology? It’s the fundamental question of life.” ~ Unknown

With this innovation we can now use the technology to understand the minute details of how life works on the nanoscale and provide answers to larger problems about the origins of life and death.

One of the biggest questions we still don’t have the answer to is, what are the different stages of cell’s life?

Cell Division

THIS IS A HUGE PROBLEM.

It’s like saying that humans go from babies → adolescence → adult → old age and then die without knowing the phases and transitions between each stage of life.

We need to know all the variations and details of a cell’s life to detect abnormalities when diseases, mutations, cancers, etc. start to occur.

Think of each cell like a teenager, undergoing the transition from a child to an adult is a difficult one and many times very stressful. We want to know how much stress a child is under to help make the transition happen smoothly. The outcomes of extreme cases are seen when students are left undiagnosed and suicide rates go up. This issue is as serious on the cellular level as it is in our society. Cells that are left undiagnosed grow into tumours and mutate which become dangerous for our health.

Optical tweezers has unleashed a new revolution in understanding the cellular biology.

Light is able to move matter because the energy in photons has momentum. This means that it exerts a force on the object it interacts with, a laser pointed towards you also pushes you away however the amount of force is so little that it’s negligible and has close to no effect. However, for particles on the nanoscale, the amount of energy in a laser has enough momentum to push the particles away.

The laser is a gaussian beam, meaning the structure of the laser will have the brightest concentrated light in the middle and the tail ends will have least. To hold the particle in place this distribution of light is necessary. In the middle of the laser a small glass ball is placed with lower refractive index so the light passing through will be refracted. On this ball you can attach the specimen you are observing.

The brighter beam of light will create net force upwards with it’s momentum because light is refracted unequally according to the gaussian profile. However with conservation of momentum there be an equal and opposite force applied to the object which brings the glass ball back to the middle. This indefinitely keeps a hold of the particles and can measure the amount of movement a specimen is causing, i.e. if a bacteria creates movement away from the optical trap in laser. The laser will act like a spring and pull the object back into middle, successfully having a hold over it.

Light being used is infrared as to not kill bacteria or cells under the radiation. This optical trap helps hold onto nanoscale objects and observe them for long periods of time. You can also move these particles as you move the whole laser beam with the glass ball in an optical trap which will also move with the direction of the laser.

Figure 1

Here is a breakdown of how this technology works, refer to the figure 1.

  1. Laser is beamed with specific wavelengths as to not harm the objects being observed.
  2. Various lens are used to create the gaussian property of laser light and allow for a more focused concentration of light as to preserve all the energy and momentum.
  3. A glass ball is placed in specimen plane where the laser light will refract accordingly and create an optical trap which will hold the object in place.
  4. A bacteria, cell, molecule, virus, etc. is attached to glass ball to hold in optical trap and observe under laser and any process of movement, reproduction, cell division is measured as force momentum changes in optical trap.
  5. Laser is adjusted accordingly and will bring glass ball back to equilibrium state.

5 Applications of Optical Tweezers:

Optical tweezers are a technology which will help observe nanoscale objects when our eyes can’t, move and manipulate them in different environments and unlock the mysteries of biological processes.

  1. Understanding the microscopic bacterial life to help better detect, prevent, and kill widespread diseases cause by infectious epidemics.
  2. Trap single cells and monitor with close observation the stages of cell division plus overall cell life to help understand, diagnose and treat cancers.
  3. Allow self-assembly of nanotech structures with contactless manipulation of molecules in optical trap.
  4. Create accurate nanometric profiles of forces released by nanoparticles to help build precise nanosystems.
  5. Trap atoms and other metals to study properties for material design and discovery.

My key takeaways:

Remember how I told you light was really important? Yup, this is just a mind-blowing application, it can literally allow us the ability to understand nanoscale objects. Still giving us the sense of sight even when the frame of reference is past our visual limitations.

  • Optical tweezers use laser technology to hold and manipulate microscopic elements.
  • We still haven’t answered basic questions in biology like understanding the life cycle of a cell, optical tweezers allow us to observe them more precisely in hopes to find the answers.
  • The nanoscale objects readily affect our everyday lives and we need to pay attention to it so we can help solve problems like cancer, diseases, and viruses.

Thank you for reading my article! I have much more research to do in the nanotech field and many more ideas to learn.

If you liked this article and wish to learn about more nanotech applications then visit my personal website at http://tanishabassan.ca/ to sign up for my newsletter where I share all new content, research, talks, events + more!

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