Asst. Prof. Michael Ross, Students, Postdocs Find Metallic Alloy Nanoparticles Absorb Higher Energies of Light

Ross lab gold and tin Image by Michael Ross

From left to right, increasing amounts of tin were added to gold nanoparticle solutions. A color change is visible as the solutions absorb higher energies of light.

By Brooke Coupal

An observation that would lead to a scientific discovery left Maria Fonseca Guzman ’21 questioning what she had seen.

“At first, I was like, ‘Is this really true?’” she recalls.

Fonseca Guzman, a senior honors chemical engineering major working in Chemistry Asst. Prof. Michael Ross’ lab at the time, found that nanoparticles made of gold and tin absorbed high energies of light.

“I remember Maria pulled me into the lab and said, ‘It’s all weird. The peaks are shifting the wrong way,’” Ross says. Fonseca Guzman had been referencing peaks on an electromagnetic spectrum plot that showed the nanoparticles absorbing blue and ultraviolet light. 

By absorbing light in a spectrum that could not be reached before, these nanoparticles could lead to advances in a variety of fields, including in medicine and energy, while reducing the use of expensive noble metals.

The surprising discovery piqued the interest of Matter, a scientific journal produced by Cell Press, which on Feb. 2 published a paper written by Ross’ lab group regarding their findings.

Creating Light-Absorbing Nanoparticles

When Ross joined UMass Lowell’s Department of Chemistry in 2019, he formed a research group interested in studying light absorption of post-transition metals: tin, bismuth, indium and gallium. The group, consisting of Fonseca Guzman and postdoctoral fellow Melissa King, attempted to create nanoparticles of pure post-transition metals; however, this proved challenging and inconsistent.

The research team then decided to mix the post-transition metals with gold, a well-studied plasmonic metal (allowing enhanced control of light), to see how the metallic alloy nanoparticles would react to light. Using an ultraviolet-visible spectrophotometer, the group found that the alloy effectively absorbed higher energies of light. 

“I did a lot of control experiments to make sure that the science was really there, and it was sound,” Fonseca Guzman says.

The team’s finding proved exciting because gold and other noble metal nanoparticles cannot absorb higher energies of light on their own, only lower-energy light like visible and infrared. By mixing in varying amounts of a post-transition metal, the team could shift absorption to blue and ultraviolet light.

Michael Ross Image by Brooke Coupal
Chemistry Asst. Prof. Michael Ross looks forward to welcoming more students and postdocs into his lab to work on groundbreaking research.

Noah Mason, an undergraduate honors chemistry major, Ph.D. chemistry student Connor Sullivan and postdoctoral fellow Sangmin Jeong joined Ross’ lab group to help collect and analyze data from the discovery. The Office of Naval Research supported the characterization of these nanoparticles through two grants totaling nearly $750,000.

In addition to using an ultraviolet-visible spectrophotometer to see where the nanoparticles are absorbing light, the team used an X-ray diffractometer, funded in part by a $127,699 National Science Foundation grant, to determine the crystal structure of the nanoparticles. King also worked with an inductively coupled plasma mass spectrometer to accurately determine the composition of the nanoparticles.

Real-Life Applications of Nanoparticles

Ross and his team focused on the fundamental science of their discovery, which could eventually help expand the applications of light-absorbing nanoparticles.

Currently, light-absorbing nanoparticles impact sensing, medicine and energy. One common use of gold nanoparticles is in COVID-19 test kits. When a COVID-19 test lights up with a pink line indicating a positive result, that’s gold nanoparticles interacting with the coronavirus antibodies.

“One reason COVID-19 tests use gold nanoparticles is that they absorb much more efficiently,” Ross says.

Ross and other researchers are also looking at how nanoparticles can be used to recycle carbon dioxide into renewable energy.

“Our work can lead to reduced precious metal usage and also to new opportunities by manipulating different energies of light,” he says.

Gaining Hands-On Lab Experience

Fonseca Guzman says she’s grateful for her time spent in Ross’ lab. 

She met Ross while looking for a lab where she could conduct her honors thesis. She is now the lead author of the Matter paper on the group’s discovery and says the experience set her up for success as she pursues a Ph.D. in physical chemistry at the University of California, Berkeley.

“A lot of my peers in my Ph.D. program did not take part in research that was as involved during their undergrad,” she says. “I was really lucky that the Honors College encourages students to pick their own research project and that you have a lot of ownership over it.”

While working in Ross' lab, Fonseca Guzman received a $5,000 fellowship from UML’s Rist Institute for Sustainability and Energy.

Noah Mason Image by Brooke Coupal
Senior chemistry major Noah Mason found his passion for research in Asst. Prof. Michael Ross' lab.
Mason received funding through an Honors College Fellowship, the Kennedy College of SciencesScience Scholars program and the Northeastern Section of the American Chemical Society.

“It can be really tough as an undergrad to get funding and support for research, so getting that funding was a real blessing,” says Mason, a co-author of the Matter paper. “It gave me the opportunity to do what I really enjoy.”

As Mason wraps up his senior year, he is looking at Ph.D. programs that will allow him to follow his passion for research.

“It’s been so much fun working in Ross’ lab on this discovery, and it’s what inspired me to do a Ph.D. program after graduating,” he says. “So, the next stage of my life, I owe to this project.”

King, another co-author of the Matter publication along with Sullivan, Jeong and Ross, finished her postdoc in Ross’ lab in May 2022 and went on to become an assistant professor in chemistry and biomolecular science at Clarkson University, where she conducts research on developing photocatalytic materials for wastewater remediation and other sustainability efforts.

“If I didn’t have the experiences that I had in Prof. Ross’ lab, I wouldn’t have the background that I need to be able to drive these projects forward,” says King, who received a fellowship from the American Association of University Women while a UML postdoc.

King appreciated the collaborative environment of Ross’ lab, which includes undergraduate and graduate students in addition to postdocs.

“It’s always good to work with people with different ideas and skill levels, because it allows you to see things from everybody’s perspective and make more well-rounded research projects,” she says.

Ross looks forward to welcoming more students and postdocs into his lab and helping them become published authors in scientific journals.

“You get to see students grow and learn new things,” he says. “And getting students published in science journals really validates their work and helps their careers.”