New Chip Watches Biology in Real-Time

The new surface plasmon polariton detector has the ability to detect the different types of proteins being secreted in cell lines, for example, which would open the doors to researchers working on tissue regeneration. CREDIT: Nicole Rager Fuller, Sayo-Art.com View full size image

This Research in Action article was provided to LiveScience in partnership with the National Science Foundation.

Researchers growing cells in petri dishes may soon be getting a new tool: a newly developed chip may help them watch their cells secrete proteins in real time, allowing them to check in on their health and productivity constantly.

The healthcare and biotechnology industries have a huge need for this kind of fast-acting, ultrasensitive, compact biosensor. It would allow researchers to watch biological processes happening in real time. The ability to detect the different types of proteins being secreted in industrial cell lines would open doors for researchers working on tissue regeneration.

The most promising devices watch these processes in real time are based on a surface plasmon polariton, a type of electromagnetic wave generated when an incident beam of light couples with an oscillating wave of electrons in the surface of a metal.

A research team led by Filbert Bartoli, professor of electrical and computer engineering at Lehigh University and member of Lehigh’s bioengineering program, reported in the journal ACS Nano that they've developed a new type of plasmonic biosensor — illustrated above — that outperforms current nanoplasmonic devices by a factor of ten.

The surface plasmon polariton detector is read with a special microscope. The results indicate if there are differences in protein concentrations on the two sides of the chip.
CREDIT: Nicole Rager Fuller, Sayo-Art.com

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Bartoli’s simple device contains two parallel, nanometer-scale slits etched a few microns apart into a thin film of silver, all deposited on a glass slide. When an incident light beam is focused onto one of those slits, the electrons at the outermost surface of the metal film oscillate, causing a surface plasmon polariton (abbreviated as SSP) to propagate along the surface of the metal.

"Two SPPs are generated," Lehigh graduate student Yongkang Gao said. "One travels along the metal-air interface on the film’s top surface and the other along the metal-glass interface on its bottom surface."

On reaching the second slit, the two waves interact, forming an interference pattern. The fringes of the interference pattern are highly dependent on the difference between the refractive indexes of the interfaces along which the waves have travelled.

The light emanating from the second slit is collected by a modified microscope, which ensures that only SPP-mediated waves are collected. The light then passes through an optical-fiber-based compact spectrometer to obtain information on the interference pattern.

"As the optical field of an SPP is strongly confined to a very thin region along the metal surface," said Bartoli, "it is extremely sensitive to changes in the local refractive index, such as those induced by proteins and other biomolecules binding to the metal surface."

The project is funded by National Science Foundation and is part of the engineering college’s Healthcare Research Cluster.

Editor's Note: Any opinions, findings, and conclusions or recommendations expressed in this material are those of the author and do not necessarily reflect the views of the National Science Foundation. See the Research in Action archive.