The healthcare industry needs fast-acting, ultrasensitive, compact biosensors that allow biological processes to be monitored in real time. Detecting the different types of proteins being secreted in cell lines would open doors for researchers working on tissue regeneration.

The most promising devices capable of achieving this 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.

Filbert Bartoli, professor and chair of the electrical and computer engineering department and member of the bioengineering program, is leading a research team that may help researchers watch their cells secrete proteins in real time. Reporting in the journal ACS Nano, the team says it developed a new type of microfluidic chip-based plasmonic biosensor that outperforms current nanoplasmonic devices by an order of magnitude.

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 (SSP) to propagate along the surface of the metal.

Graduate student Yongkang Gao explains that “two SPPs are generated. 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.

"As the optical field of an SPP is strongly confined to a very thin region along the metal surface," says 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 the National Science Foundation and is part of the engineering college’s Healthcare Research Cluster.

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