Oil-in-water droplets respond to chemical cues by forming arm-like extensions that resemble filopodia, which are used by living cells to sense and explore their environment. A research team led by chemists at Penn State studies the droplets to glimpse how matter may have transitioned to life billions of years ago. The researchers dissected the mechanism through which these arms form and showed that they respond directionally, growing toward or away from specific chemicals.
The research was published online in the Journal of the American Chemical Society and will be featured on the front cover of an upcoming issue. The society also featured the research in its Research Headlines video series, which spotlights new and interesting work published in the society's journals.
"Life if so complex and organized that it can be difficult to imagine the many steps it must have taken for the matter-to-life transition," said Ayusman Sen, Verne M. Willaman Professor of Chemistry at Penn State and the leader of the research team. "This work represents one little piece in the puzzle. We show that simple droplets of oil are cell mimics and behave in life-like ways, responding to environmental cues in ways that many living cells do."
Key findings
- Filopodia form as droplets of certain oils begin to solubilize - or dissolve - in a mixture of water and a surfactant - a key chemical ingredient in soaps that reduce surface tension in liquids.
- The filopodia form because the surfactant molecules enter the oil droplets, forming mechanically unstable layers on their surfaces, and extend out from the droplets.
- Filopodia preferentially form in the direction of higher surfactant concentrations.
- Filopodia form toward or away from higher concentrations of certain amino acids - the building blocks of proteins - depending on their chemical properties. This behavior is also found in many unicellular organisms.
"We are interested in developing artificial systems that mimic cellular behaviors to help us understand the matter-to-life transition that occurred on the early Earth, three-to-four billion years ago," said Sanjana Krishna Mani, a graduate student in chemistry in the Eberly College of Science at Penn State and the first author of the paper. Krishna Mani received the Best Poster Award for this work, which she presented at the 2025 Materials Day hosted by the Penn State Materials Research Institute in October. "Our findings could also help in the design of lifelike materials that respond to their environments."
In addition to Krishna Mani and Sen, the research team from Penn State includes Samuel G. Birrer, graduate student in chemistry; Aditya Sapre, graduate student in chemical engineering; and Lauren D. Zarzar, professor of chemistry. Laurie Lazinski, a teacher at Northville Central School District in New York also contributed.
The Sloan Foundation funded the research. The Penn State Huck Institutes for the Life Sciences and the Penn State MRSEC-Center for Nanoscale Science Research Experience for Teachers (RET) program funded by the U.S. National Science Foundation provided additional support.
