A sharper image for proteins

April 29, 2022

Proteins may be the most important and varied biomolecules within living systems. These strings of amino acids, assuming complex three-dimensional forms, are essential for the growth and maintenance of tissue, the initiation of thousands of biochemical reactions, and protecting the body from pathogens through the immune system. They play a central role in health and disease, and they are primary targets for pharmaceutical drugs.

To fully understand proteins and their myriad functions, researchers have developed sophisticated means to see and study them through advanced microscopy, improving light detection, imaging software and the integration of advanced hardware systems. Graphic illustration of the experimental setup for performing evanescent scattering microscopy. This graphic shows the experimental setup for performing evanescent scattering microscopy. The technique is a label-free method for sensitive imaging of biomolecules, including proteins. A beam of laser light is directed at a molecular sample with the proper angle to produce a condition known as total internal reflection. The resulting evanescent wave can excite the molecules at the glass-liquid interface, allowing for exceptionally precise imaging. Download Full Image

In a new study, corresponding author Shaopeng Wang and his colleagues at Arizona State University describe a new technique that promises to revolutionize the imaging of proteins and other vital biomolecules, allowing these tiny entities to be visualized with unprecedented clarity and by simpler means than existing methods.

"The method we report in this study uses normal cover glass instead of gold-coated cover glass, which has two advantages over our previously reported label-free, single-protein imaging method," Wang says. "It is compatible with fluorescence imaging for in situ cross validation, and it reduces the light-induced heating effect that could harm the biological samples. Pengfei Zhang, an outstanding postdoctoral researcher in my group, is the technical lead of this project."

Wang has a joint faculty position in the Biodesign Center for Bioelectronics and Biosensors and School of Biological and Health Systems Engineering. The group’s research findings appear in the current issue of the journal Nature Communications.

The new method, known as evanescent scattering microscopy (ESM), is based on an optical property first recognized in antiquity, known as total internal reflection. This occurs when light passes from a high-refractive medium (like glass) into a low-refractive medium (like water).

When the angle of incident light is moved away from the perpendicular (relative to the surface), it eventually reaches the “critical angle,” resulting in all the incident light being reflected, rather than passing through the second medium. (To properly illuminate biological samples, laser light is used.)

ASU researcher Shaopeng Wang smiling and wearing a white lab coat.

Shaopeng Wang is a researcher in the Biodesign Center for Bioelectronics and Biosensors and the School of Biological and Health Systems Engineering at ASU.

Total internal reflection produces an evanescent field, which can excite cells or molecules like proteins at the glass-water interface, when such molecules are affixed to a cover glass, allowing researchers to visualize them in startling detail.

Previous methods commonly label the biomolecules of interest with fluorescent tags known as fluorophores, to better image them. This process can interfere with the subtle interactions being observed and requires cumbersome sample preparation. The ESM technique is a label-free imaging method requiring no fluorescent dye or gold coating for sample slides.

Instead, the method exploits subtle irregularities in the surface of the cover glass to produce images of razor-sharp contrast. This is achieved by imaging the interference of evanescent light scattered by the single-molecule samples and the rough texture of the cover glass.

The use of evanescent wave scattering allows samples, including proteins, to be probed at extremely shallow depth, typically less than 100 microns. This allows ESM to create an optical slice, with dimensions comparable to a thin electron microscopy section.

The new study describes the use of ESM to detect four model proteins: bovine serum albumin (BSA), mouse immunoglobulin G (IgG), human immunoglobulin A (IgA) and human immunoglobulin M (IgM).

Protein-protein interactions, including the rapid binding and dissociation of individual proteins, were observed in a series of experiments. Understanding such binding kinetics is essential for the design of safer and more effective drugs. The researchers also used ESM to keenly observe conformational changes in DNA, further demonstrating the power and versatility of the new method.

Richard Harth

Science writer, Biodesign Institute at ASU


Global health PhD graduate focuses her career on sexual, reproductive health

April 29, 2022

Editor's note: This story is part of a series of profiles of notable spring 2022 graduates.

Janet Nalubega Ross has spent her life drawn to health care and sexual health. She says the journey started for her growing up in post-war Uganda.  Janet Nalubega Ross Photo courtesy Janet Nalubega Ross. Download Full Image

“On top of coming out of the civil war, we were hit by the AIDS epidemic, and HIV/AIDS started becoming a thing,” Ross said. “I grew up in this very interesting time where everyone was talking about this.” 

Ross, who goes by her middle name Nalubega, came to the United States when she was 18 years old to attend college. Throughout her educational career, she obtained a BA in community health education and a master’s degree in bioinformatics. 

“Bioinformatics is a statistics degree for people who really want to work with biological data,” Ross said. “So that’s when scientists do all of these experiments and produce a lot of data, or for people like me who want to analyze big health data sets.”  

While obtaining her degrees, Ross volunteered at domestic violence shelters and rape recovery centers. She volunteered at Planned Parenthood, taught sex education to high school students and worked at a free clinic. 

“I’ve always had a passion for anything sexual health and sexuality-related,” Ross said. “Even though I was interested in sex, I started to see how there were other things outside of sex that affected people’s health, particularly women’s health.” 

After receiving her master’s degree, Ross taught for a while, but then took time off to spend time with her daughter and husband. It was at this point Ross wanted to focus back on her education and started looking for PhD programs. She was drawn to the global health program at ASU’s School of Human Evolution and Social Change

“I was really attracted to the ASU program because it looked very holistic, it focused on not just the person, but the data and it was very interdisciplinary.” 

Leading up to commencement, we asked Ross a few questions about her time at ASU and her advice for students. 

Answers have been edited for length and clarity.

Question: What was your “aha” moment when you realized you wanted to study the field you majored in?

Answer: My aha moment was interesting. The advice I was given when I started my PhD in particular was that you read about your field and find the gap, and try and see if you can fill the gap. I’m in global health and I’ve read all these global health papers, and the biggest thing that was being talked about was there was a gap in the way we discuss adolescent mental health globally, so I thought that sounded interesting and wanted to do that. 

I started reading up on it and it was very boring to me. And for me to do it correctly, I felt like I had to take a lot of classes I’ve never really taken, like psychology and childhood development. I felt like I had to take these classes to do it in a way that felt holistic and to honor the people I would be interviewing and working with. 

I just came home one day and I turned to my husband and I said, “I can't do adolescent mental health.” And he said, “Well, what do you want to do?” "I want to talk to people about their sex lives, how they learned about sex and sexual health and reproductive health." So I met with my advisor asked her if I could change my focus to reproductive and sexual health, and she said yes. 

This was during my second semester of PhD school, and it felt like a huge burden had been lifted off my shoulders. I was happy I could do the research I’ve been interested in my whole life, that I love and enjoy.  

Q: Which professor taught you the most important lesson while at ASU?

A: I would say Professor Monica Gaughan because we work so closely together. Gaughan was my dissertation co-chair and I worked for her as a research assistant. 

The biggest thing that she ever taught me is that you can have a life outside your research. She was the one who taught me to have a good work-life balance. And having a good work-life balance would still make you a successful researcher or student. This has really helped me put things into perspective, especially when doing research and trying to know what's important to me and what do I need to get done. I have a husband, a kid and multiple hobbies. 

Q: What’s the best piece of advice you’d give to those still in school?

A: Take time off. If you look at all my education trajectories, I always took a year or two off, or three, before I got the next degree. Doing this gave me perspectives that really helped my education. It also allowed me to travel with my partner and my kid. 

Taking time allowed me to build a community that supported me through my PhD who are not academics.

Nicole Pomerantz

Communications specialist, School of Human Evolution and Social Change