Penn molecular scientists develop colour-changing stress sensor

Penn molecular scientists develop colour-changing stress sensor

12:24 PM, 19th August 2011
Penn molecular scientists develop colour-changing stress sensor
Enhanced image of a polymersome changing color under stress.


PHILADELPHIA, US: It is helpful - even life-saving - to have a warning sign before a structural system fails, but, when the system is only a few nanometre in size, having a sign that’s easy to read is a challenge. Thanks to a clever bit of molecular design by University of Pennsylvania and Duke University bioengineers and chemists, such warning can come in the form of a simple colour change.  

The study was conducted by Professor Daniel Hammer and Graduate Students Neha Kamat and Laurel Moses of the Department of Bioengineering in Penn’s School of Engineering and Applied Science. They collaborated with Associate Professor Ivan Dmochowski and Graduate Student Zhengzheng Liao of the Department of Chemistry in Penn’s School of Arts and Sciences, as well as Professor Michael Therien and Graduate Student Jeff Rawson of Duke. 

Their work was published in the journal Proceedings of the National Academy of Sciences.

The researchers’ work involves two molecules: porphyrins, a class of naturally occurring pigments and polymersomes, artificially engineered capsules that can carry a molecular payload in their hollow interiors. In this case, Kamat and Liao hypothesized that polymersomes could be used as stress sensors if their membranes were embedded with a certain type of light-emitting porphyrins.

The Penn researchers collaborated with Therien lab, where the porphyrins were originally developed, to design polymersomes that were studded with the light-emitting molecules.

“When you package these porphyrins in a confined environment, such as a polymersome membrane, you can modulate the light emission from the molecules,” said Hammer. “If you put a stress on the confined environment, you change the porphyrin’s configuration, and, because their optical release is tied to their configuration, you can use the optical release as a direct measure of the stress in the environment.”

For example, the labeled polymersomes could be injected into the blood stream and serve as a proxy for neighbouring red blood cells. As both the cells and polymersomes travel through an arterial blockage, for example, scientists would be able to better understand what happens to the blood cell membranes.  

The researchers calibrated the polymersomes by subjecting them to several kinds of controlled stresses and measuring their colour changes. The measurements must be made by computers, rather than the naked eye.

“These kinds of tools could be used to monitor drug delivery, for example,” said Kamat. “If we have a way to see how stressed the container is over time, we know how much of the drug has come out.”

And, though the researchers chose the engineered polymersomes due to the wide range of stress they can endure, the same stress-labeling technique could soon be applied directly to naturally occurring tissues.

The work was supported by the National Institutes of Health, the National Science Foundation and its Materials Research Science and Engineering Centre programme and the National Centre for Research Resources.

Kamat is an NSF Graduate Fellow.

(C) University of Pennsylvania News




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