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mPOF includes internal biosensor

14 Feb 2007

Researchers in Denmark unveil a fiber-optic biosensor made from a microstructure polymer optical fiber (mPOF) that features internal localized sensing regions.

Danish researchers have created an unusual fiber-optic biosensor by exploiting the properties of microstructured polymer optical fiber (mPOF) fabricated from a material called Topas. The team's device contains localized sensing regions within the air holes that run along the length of the fiber (Optics Letters 32 460).

"We believe this is the first mPOF to be fabricated from Topas cyclic olefin copolymer," stated the authors.

Traditionally, mPOFs are fabricated from polymethyl methacrylate (PMMA) and their optical properties are dictated by the relative position, size and shape of the internal air holes.

"Topas has attractive material properties (no monomers and very low moisture absorption – about 100 times lower than that of PMMA) and it is also chemically inert," explained the authors. "It exhibits an improved melt viscosity and high tear strength, allowing better conditions for drawing optical fibers."

Researcher Grigoriy Emiliyanov from Technical University Denmark told optics.org that the starting point is a preform 70 mm in length and 25 mm in diameter. "We have drawn around 250 m of Topas mPOF in around 30 minutes," he said. "The mPOF has three holes running along its length, each around 50 μm in diameter."

To turn the fiber into a biosensor, Emiliyanov and colleagues exploit the fact that Topas is chemically inert and direct binding of biomolecules onto its surface is difficult.

"Commercially available Antraquinion (AQ) linker molecules can attach to the Topas surface when activated with UV light and can then accept sensor layers," explained the authors. "As a consequence, a UV mask can be used to define localized sensor layers inside a Topas mPOF."

The team filled a 30 cm long Topas mPOF with a solution containing AQ molecules. After a 1 hour incubation period, half of the fiber was illuminated with a UV lamp emitting at 325 nm, resulting in localized binding of AQ molecules, which in turn created localized sensing layers via an antigen-antibody binding-detection procedure. Analysis using fluorescently labelled antibodies confirmed that the sensing layer existed only where the fiber had been exposed to UV light.

"We believe that the possibility of defining the sensing layer locally in a section of the fiber introduces the possibility if up-concentrating the target molecules in a confined region," said Emiliyanov. "This is advantageous for grating-based sensor configurations for label-free detection of biomolecules."

"The next step is to improve the fabrication process and be able to draw Topas mPOF with better guiding properties, such as singlemode," concluded Emiliyanov.

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