Abstract
We present experimental results showing that long-period gratings in photonic crystal fibers can be used as sensitive biochemical sensors. A layer of biomolecules was immobilized on the sides of the holes of the photonic crystal fiber and by observing the shift in the resonant wavelength of a long-period grating it was possible to measure the thickness of the layer. The long-period gratings were inscribed in a large-mode area silica photonic crystal fiber with a CO2 laser. The thicknesses of a monolayer of poly-L-lysine and double-stranded DNA was measured using the device. We find that the grating has a sensitivity of approximately 1.4nm/1nm in terms of the shift in resonance wavelength in nm per nm thickness of biomolecule layer.
Highlights
Optical fibers are finding increasing application as sensors within biochemistry [1, 2, 3, 4]
The measured transmission spectrum of the Photonic crystal fibers (PCFs)-long-period grating (LPG) was interpolated with a polynomial of high order, which was used to find the peak of the transmission dip corresponding to the resonant wavelength of the PCF-LPG
The PCF-LPG was tested with respect to the sensitivity of the resonant wavelength, λres, on temperature
Summary
Optical fibers are finding increasing application as sensors within biochemistry [1, 2, 3, 4]. Other techniques for biochemical sensing with optical fibers include surface plasmon resonance [7] and Fabry-Perot micro cavities used as an interferometric sensor [8]. Photonic crystal fibers (PCFs) [9] are optical fibers penetrated throughout their length by an array of microscopical holes. These fibers have unique light guiding properties and their array of air holes may hold a sample volume of a few nanoliters per cm of fiber. The contents of these holes, for example gases and liquids, may be probed using the evanescent-wave sensing principle [11]. Microstructured polymer optical fibers [12] are well suited for biosensing [13] since polymers allow a wide range of surface chemistries to be used
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