Nav: Home

Making higher-energy light to fight cancer

December 02, 2019

Materials scientists at the University of California, Riverside and The University of Texas at Austin have demonstrated that it is possible to achieve photon up-conversion, the emission of light with energy higher than the one that excites the material, when using carefully designed structures containing silicon nanocrystals and specialized organic molecules.

The accomplishment, published in Nature Chemistry, brings scientists one step closer to developing minimally invasive photodynamic treatments for cancer. The advance could also hasten new technologies for solar-energy conversion, quantum information, and near-infrared driven photocatalysis.

High energy light, such as ultraviolet laser light, can form free radicals able to attack cancer tissue. Ultraviolet light, however, doesn't travel far enough into tissues to generate therapeutic radicals close to the tumor site. On the other hand, near-infrared light penetrates deeply but doesn't have enough energy to generate the radicals.

While photon up-conversion can overcome this limitation, up-converted materials have either low efficiency or are based on toxic materials. Silicon is well-known for being nontoxic, but until now, researchers have not been able to demonstrate that silicon nanocrystals can up-convert photons, leaving this promising cancer treatment tantalizingly out of reach.

A group led by UC Riverside materials science doctoral student Pan Xia attacked this problem by carefully studying the surface chemistry of silicon nanocrystals. The group learned how to attach ligands, which help bind molecules together, to the nanoparticle that are specifically designed to transfer the energy from the nanocrystals to surrounding molecules.

The team then shined laser light into the solution. They found silicon nanocrystals with appropriate surface ligands can rapidly transfer the energy to the triplet state of surrounding molecules. A process called triplet-triplet fusion then converts the low-energy excitation to a high energy one, resulting in the emission of a photon at shorter wavelength, or higher energy, than the one originally absorbed by the nanoparticle.

"We functionalized silicon nanocrystals with anthracene. Then we excited the silicon nanocrystals and found that the energy was efficiently transferred from the nanocrystal, through the anthracene molecules, to the diphenylanthracene in solution," said Xia. "It means we got higher-energy light."

"To turn the low-energy photons into high-energy photons, you need to use triplets, you need to use quantum confined nanoparticles, and you need to hold the nanoparticles and the organic molecules very close together. This is how you get the triplets to combine energy to get the high energy photons," said co-author Ming Lee Tang, an associate professor of chemistry at UC Riverside and Xia's dissertation adviser. Tang's lab pioneered how to attach conjugated organic molecules to the silicon nanoparticles.

"This work is very fundamental," said co-author Lorenzo Mangolini, an associate professor of mechanical engineering, whose group made the silicon nanocrystals. "The novelty is really how to get the two parts of this structure -- the organic molecules and the quantum confined silicon nanocrystals -- to work together. We are the first group to really put the two together."

Co-author Sean Roberts, an assistant professor of chemistry at The University of Texas at Austin, used ultrafast lasers to investigate how energy is transferred in this hybrid structure, and determined the process is both amazingly fast and efficient.

"The challenge has been getting pairs of excited electrons out of these organic materials and into silicon. It can't be done just by depositing one on top of the other," said Roberts. "It takes building a new type of chemical interface between the silicon and this material to allow them to electronically communicate."

The discovery could also lead to improved photocatalysis, which uses light to drive chemical reactions.

"Photocatalysts generally only work with ultraviolet light or violet light, so this is a way to generate that from the rest of the solar spectrum," Tang said.

The environmentally sustainable silicon-centered approach is also relevant for quantum information science and singlet fission-driven solar cells.
The paper, "Achieving spin-triplet exciton transfer between silicon and molecular acceptors for photon upconversion," was published Dec. 2 in Nature Chemistry. Other authors include Emily K. Raulerson, Devin Coleman, and Carter S. Gerke.

Funding for the research was provided by the National Science Foundation, the Robert A. Welch Foundation, the Research Corporation for Science Advancement, the Air Force Office of Scientific Research and the Department of Energy.

About UC Riverside

The University of California, Riverside is a doctoral research university, a living laboratory for groundbreaking exploration of issues critical to Inland Southern California, the state and communities around the world. Reflecting California's diverse culture, UCR's enrollment is more than 24,000 students. The campus opened a medical school in 2013 and has reached the heart of the Coachella Valley by way of the UCR Palm Desert Center. The campus has an annual statewide economic impact of almost $2 billion. To learn more, email>

University of California - Riverside

Related Science Articles:

75 science societies urge the education department to base Title IX sexual harassment regulations on evidence and science
The American Educational Research Association (AERA) and the American Association for the Advancement of Science (AAAS) today led 75 scientific societies in submitting comments on the US Department of Education's proposed changes to Title IX regulations.
Science/Science Careers' survey ranks top biotech, biopharma, and pharma employers
The Science and Science Careers' 2018 annual Top Employers Survey polled employees in the biotechnology, biopharmaceutical, pharmaceutical, and related industries to determine the 20 best employers in these industries as well as their driving characteristics.
Science in the palm of your hand: How citizen science transforms passive learners
Citizen science projects can engage even children who previously were not interested in science.
Applied science may yield more translational research publications than basic science
While translational research can happen at any stage of the research process, a recent investigation of behavioral and social science research awards granted by the NIH between 2008 and 2014 revealed that applied science yielded a higher volume of translational research publications than basic science, according to a study published May 9, 2018 in the open-access journal PLOS ONE by Xueying Han from the Science and Technology Policy Institute, USA, and colleagues.
Prominent academics, including Salk's Thomas Albright, call for more science in forensic science
Six scientists who recently served on the National Commission on Forensic Science are calling on the scientific community at large to advocate for increased research and financial support of forensic science as well as the introduction of empirical testing requirements to ensure the validity of outcomes.
World Science Forum 2017 Jordan issues Science for Peace Declaration
On behalf of the coordinating organizations responsible for delivering the World Science Forum Jordan, the concluding Science for Peace Declaration issued at the Dead Sea represents a global call for action to science and society to build a future that promises greater equality, security and opportunity for all, and in which science plays an increasingly prominent role as an enabler of fair and sustainable development.
PETA science group promotes animal-free science at society of toxicology conference
The PETA International Science Consortium Ltd. is presenting two posters on animal-free methods for testing inhalation toxicity at the 56th annual Society of Toxicology (SOT) meeting March 12 to 16, 2017, in Baltimore, Maryland.
Citizen Science in the Digital Age: Rhetoric, Science and Public Engagement
James Wynn's timely investigation highlights scientific studies grounded in publicly gathered data and probes the rhetoric these studies employ.
Science/Science Careers' survey ranks top biotech, pharma, and biopharma employers
The Science and Science Careers' 2016 annual Top Employers Survey polled employees in the biotechnology, biopharmaceutical, pharmaceutical, and related industries to determine the 20 best employers in these industries as well as their driving characteristics.
Three natural science professors win TJ Park Science Fellowship
Professor Jung-Min Kee (Department of Chemistry, UNIST), Professor Kyudong Choi (Department of Mathematical Sciences, UNIST), and Professor Kwanpyo Kim (Department of Physics, UNIST) are the recipients of the Cheong-Am (TJ Park) Science Fellowship of the year 2016.
More Science News and Science Current Events

Trending Science News

Current Coronavirus (COVID-19) News

Top Science Podcasts

We have hand picked the top science podcasts of 2020.
Now Playing: TED Radio Hour

Listen Again: Meditations on Loneliness
Original broadcast date: April 24, 2020. We're a social species now living in isolation. But loneliness was a problem well before this era of social distancing. This hour, TED speakers explore how we can live and make peace with loneliness. Guests on the show include author and illustrator Jonny Sun, psychologist Susan Pinker, architect Grace Kim, and writer Suleika Jaouad.
Now Playing: Science for the People

#565 The Great Wide Indoors
We're all spending a bit more time indoors this summer than we probably figured. But did you ever stop to think about why the places we live and work as designed the way they are? And how they could be designed better? We're talking with Emily Anthes about her new book "The Great Indoors: The Surprising Science of how Buildings Shape our Behavior, Health and Happiness".
Now Playing: Radiolab

The Third. A TED Talk.
Jad gives a TED talk about his life as a journalist and how Radiolab has evolved over the years. Here's how TED described it:How do you end a story? Host of Radiolab Jad Abumrad tells how his search for an answer led him home to the mountains of Tennessee, where he met an unexpected teacher: Dolly Parton.Jad Nicholas Abumrad is a Lebanese-American radio host, composer and producer. He is the founder of the syndicated public radio program Radiolab, which is broadcast on over 600 radio stations nationwide and is downloaded more than 120 million times a year as a podcast. He also created More Perfect, a podcast that tells the stories behind the Supreme Court's most famous decisions. And most recently, Dolly Parton's America, a nine-episode podcast exploring the life and times of the iconic country music star. Abumrad has received three Peabody Awards and was named a MacArthur Fellow in 2011.