Know five reasons why physicists like microscopes

Rema Krishnaswamy, physicist and keeper of microscopes at Azim Premji University, shares ways in which microscopes are useful in Physics and how it led to the initiation of the microscopy facility at Azim Premji University, with Nandita Jayaraj.

Rema Krishnaswamy and microscopy facility 1

Microscopes are commonly associated with Biology, but it may surprise many of us that they are just as useful for physicists.

With 15 years of research in the field of Soft Matter Physics under her belt, Rema Krishnaswamy is no stranger to the immense possibilities that a microscope brings to a Physics laboratory or classroom.

That’s why she and her biologist colleague, Sravanti Uppaluri, were motivated to initiate a microscopy facility at Azim Premji University when they joined six years ago.

Rema Krishnaswamy, Faculty, Azim Premji University

As an experimental scientist, I wanted the curriculum to be hands-on, centered on experimentation. I wanted to bring to the University something from my research, and a [light] microscope seemed like the right thing,” said Rema.

With it, we can design very interesting experiments even at the undergraduate level. Students get a flavour of current research and I feel that has a lot of educational value,” added Rema.

Fast forward to 2022, the microscopy facility at Azim Premji University seems to be a definite success story. Not only has it proved to be a great teaching tool, but it has also been extremely valuable for research undertaken by faculty and students at the University.

Rema was deeply moved by an email she recently received from her ex-student who had worked with her on his honours project, and is pursuing a Master’s degree at a prestigious lab in Paris.

If I’m in this lab, then it’s because I worked with you,’ wrote the student in the email. Rema hopes to see a future where more physics students carry forth the microscope-sourced knowledge they have gathered not just to embark upon research, but also in other fields.

We are hoping that students will end up doing not only PhDs, but also become entrepreneurs. We want to get more of them interested in instrumentation, teaching, developing kits for education and so on.”

So, what does a physicist do with a microscope, anyway? Here are five ways that Rema has used microscopes in her role as a scientist and a physics educator at the University.

#1 To observe Brownian motion

In 1827, botanist Robert Brown famously observed pollen grains constantly jiggling in water. Years later in 1905, Einstein analysed this Brownian’ motion and proved a theory that showed liquids really are made of atoms. He showed that this jiggling motion is essentially a random walk executed by the particles when constantly bombarded by fluid molecules.

In the lab, Rema’s students have had the opportunity to actually see these particles flickering about. They even tracked the motion of these particles under a microscope and plotted how they move in time.

This was what Jean Perrin did in 1908 to experimentally prove Einstein’s theory. Perrin would go on to win a Nobel Prize for his work.

Back in Perrin’s time, this was a very difficult experiment. A lot of chemistry was required to achieve precise sizes of the particles. Nowadays, you can get well-defined sizes of colloidal particles, and UG students can easily do this experiment. It would not be possible without a microscope,” said Rema.

With these experiments, students at Azim Premji University have been able to actually calculate oft-cited, but abstract-seeming terms in Physics and Chemistry such as Boltzmann constant and Avogadro Number.

This is not something I could do even in my postgraduate days, forget undergraduate,” she said.

Of course, the students will then find that sometimes the value they calculate doesn’t match the actual value. But then they learn to appreciate the kind of errors that can creep in, and how experiments require very careful measurements. It really made a difference…” 1

Observing Brownian motion at a workshop in 2019​. The constantly moving specks on the wall are proof of the scattering of light​from the Brownian particles.

Credit: Rema Krishnaswamy

#2 To study the structure of milk

A soft matter physicist doesn’t look at milk as a beverage as the rest of us would tend to. When Rema thinks of milk, she thinks of a colloidal emulsion comprising fat globules and protein micelles suspended in an aqueous medium.

In her advanced soft condensed matter’ elective, Rema’s students are asked to observe milk under different conditions. For example, they add salt to curdle it, or acid to change its pH. You can design nice quantitative experiments with light or a phase contrast microscope based on this,” she says.

A microscopic view of milk under a phase contrast microscope.

#3 To create diffraction patterns of crystals

Rema had used X‑ray diffraction – a technique to determine the structure of a crystal – extensively in her research. So, she wondered how she could bring some of that to the classroom.

X‑rays, of course, are too high maintenance, so she decided to see if she could replace them with light. But just shining light on molecular crystals doesn’t give much information,” she said.

Rema and her students made crystals of colloidal particles instead. This was relatively easy for students to do in the classroom, using techniques such as slow evaporation or merely allowing the particles to clump together fast under gravity.

They then observed the structure of these crystals under the microscope. The students can create a diffraction pattern through a Fourier Transform (FT) of the image. They can also obtain a diffraction pattern by shining a laser on these crystals, and compare the two patterns they got.”

Two-dimensional colloidal crystals

Credit: Rema Krishnaswamy

#4 To image super thin nanofilms

Nanofilms are making news for very good reasons. These ultra-thin layers of molecules have very special properties that have various applications such as in energy harvesting. It’s easy to generate a nanofilm at home — all it takes is to spread a drop of soap or olive oil on water.

But Rema points out the challenges that lie in the way of studying them: I can’t just form a film and look at it under a microscope because it’s so thin that any light that falls on it just gets transmitted through. Unless there is a contrast or a scattering from the surface, there’s no way you can see it.”

Luckily, this is exactly the kind of challenge physicists love, and sure enough, they have developed various ways to work through this.

Two types of microscopy that have evolved to tackle this are Total Internal Reflection Fluorescence Microscopy (TIRFM) and Brewster Angle Microscopy (BAM).

A 30 nm thick nanofilm captured via an optical microscope.

Credit: Wikimedia Commons/​Moiseenko_​E_​T

#5 To get to the core of instrumentation

For her core courses like Optics, Rema starts out by asking her students to build a simple microscope with just two lenses. She further asks them how they would determine the magnification of their DIY (Do It Yourself) microscope.

When the lab went online, we asked them to design a cheap microscope with a mobile camera and glass bead or drop of liquid, and use this to observe onion cells.”

Rema finds immense value in introducing her students to different techniques like bright field microscope and phase contrast microscope. She believes it is a way to motivate them to the field of instrumentation, and perhaps inspire them to build affordable microscopes to introduce in small labs and in schools in villages.

It’s not just a matter of showing them a high-end microscope, but also a way to adapt it to different ways and designing something that is better.”

Rema conducting a microscopy workshop for teachers.

Credit: Rema Krishnaswamy