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20 August 2009Polymer photonic crystal dye lasers as label free evanescent cell sensors
Dye doped polymer photonic crystal band edge lasers are applied for evanescent wave sensing of cells. The lasers
are rectangular shaped slab waveguides of dye doped polymer on a glass substrate, where a photonic crystal
is formed by 100 nm deep air-holes in the surface of the 375 nm high waveguides. The lasers are fabricated
by combined nanoimprint and photolithography (CNP) in Ormocore hybrid polymer doped with the laser dye
Pyrromethene 597. The lasers emit in the chip plane at a wavelength around 595 nm when pumped with 5 ns
pulses from a compact frequency doubled Nd:YAG laser. We investigate the sensitivity of photonic crystal band-edge
lasers to partial coverage with HeLa cells. The lasers are chemically activated with a flexible UV activated
anthraquinone based linker molecule, which enables selective binding of cells and molecules. When measuring in
Phosphate Buffered Saline (PBS), which has a refractive index close to that of the cells, the emission wavelength
depends linearly on the cell density on the sensor surface. Our results demonstrate that nanostructured hybrid
polymer lasers, which are cheap to fabricate and very simple to operate, can be selectively chemically activated
with UV sensitive photolinkers for further bioanalytical applications. This opens the possibility to functionalize
arrays of optofluidic laser sensors with different bio-recognition molecules for multiplexed sensing. The linear
relationship between cell coverage and wavelength indicates that the slight refractive index perturbation from
the partial coverage of the sensor influences the entire optical mode, rather than breaking down the photonic
crystal feedback.