Fluorescent “dots” (that is, tiny particles that can emit light) have a multitude of promising biomedical applications, from helping doctors better identify tumor margins to delivering a drug deep within the body. However, making these points is usually a long and tedious process that uses harsh chemicals. Now, NIBIB-funded researchers are developing a fluorescent dot that is not only easier to manufacture, but uses environmentally friendly materials.
“This proof-of-principle study describes a new ‘green’ approach to fabricating fluorescent nanomaterials, which are promising molecules in the biomedical field,” said Tatjana Atanasijevic, Ph.D., director of the NIBIB program in Molecular Probes and Imaging Agents. “The research described here provides fundamental information that could lead to a cheaper and safer way to synthesize this important type of nanoparticle.”
Traditional fluorescent dot synthesis methods typically require the use of organic solvents, which are effective in helping to break down substances and facilitating chemical reactions. However, organic solvents can be flammable, volatile and carcinogenic, and potentially dangerous if handled incorrectly. Furthermore, the synthesis of fluorescent dots is often complex and time-consuming, presenting a variety of challenges for large-scale manufacturing.
But researchers at the University of Nebraska Medical Center (UNMC) are working on an alternative strategy. They combine hyaluronic acid, a common carbohydrate, along with specific amino acids (the molecules that make up proteins). Both components are abundant in our body and, more importantly, both can dissolve in water. This last feature eliminates the need for toxic organic solvents.
“Unlike traditional fluorescent dots, our dots combine two natural materials,” explained the study’s senior author, Aaron Mohs, Ph.D., associate professor in the department of pharmaceutical sciences at UNMC. “Not only does this facilitate the synthesis of our nanomaterial, as we can purify the spots using only water, but it also takes advantage of the biocompatibility of these molecules, potentially making them an ideal nanoparticle for a variety of different environments.” Mohs’ research on these fluorescent spots was recently reported in the diary ACS Omega.
Typically, when researchers make fluorescent particles, they use a starting material that has fluorescent properties. However, neither hyaluronic acid nor amino acids are particularly fluorescent on their own. To make their dots shine, Mohs and his colleagues take advantage of the unique chemistry that occurs when these materials are combined. As hyaluronic acid interacts with certain amino acids, the electrons shared by these molecules can become confined, affecting the way the electrons react when exposed to particular wavelengths of light. This phenomenon is known as cross-linking enhanced emission. The result? The dots glow blue under specific conditions, allowing the nanoparticles to be visualized in the cells.
Beyond biomedical imaging applications, the researchers wanted to investigate whether these fluorescent nanoparticles could be used for drug delivery. They loaded their dots with doxorubicin, a common cancer chemotherapeutic, and evaluated its drug delivery properties and cytotoxic effects. Compared to standard doxorubicin, doxorubicin-loaded dots released drug more slowly in standard drug release assays and showed greater killing of breast cancer cells. “While an appreciable amount of standard doxorubicin is pumped out of cells through drug efflux mechanisms, when we trap the drug within the dot, we are likely preventing this effect somewhat,” explained the study’s first author, Deep Bhattacharya, Ph.D., who is now a senior scientist at Pfizer. “This entrapment in the nanodot allows for increased therapeutic loading and prolonged release of doxorubicin into the cells.”
Mohs noted that this proof-of-concept work is just the beginning for their fluorescent dots. “We would like to make further modifications to these spots to improve them for biological detection in tissues,” he said. “But this initial study demonstrated the imaging and drug delivery properties of these dots, which we can make using environmentally friendly materials.”
This study was funded by National Institute of Biomedical Imaging and Bioengineering (NIBIB) grant R01EB019449 and National Cancer Institute (NCI) grants R21CA212500 and P30CA036727.
Study reference: Deep S. Bhattacharya, Aishwarya Bapat, Denis Svechkarev and Aaron M. Mohs. Water-soluble blue fluorescent non-conjugated polymer dots of hyaluronic acid and hydrophobic amino acids. ACS Omega 2021 6 (28), 17890-17901. DOI: 10.1021/acsomega.1c01343
This Science Highlight describes a basic research finding. Basic research increases our understanding of human behavior and biology, which is critical to promoting new and better ways to prevent, diagnose, and treat diseases. Science is an unpredictable and incremental process: each research advance builds on past discoveries, often in unexpected ways. Most clinical advances would not be possible without knowledge of fundamental basic research.
About the artwork: This graphic was adapted for this highlight and is licensed under a Creative Commons license. Attribution-NonCommercial-NoDerivatives 4.0 International license.
