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Sensors 2009, 9(11), 8382-8390; doi:10.3390/s91108382

Material Limitations on the Detection Limit in Refractometry

1 Department of Micro and Nanotechnology, Technical University of Denmark, DTU Nanotech, Building 345 East, DK-2800 Kongens Lyngby, Denmark 2 Department of Photonics Engineering, Technical University of Denmark, DTU Fotonik, Building 345 West, DK-2800 Kongens Lyngby, Denmark
* Author to whom correspondence should be addressed.
Received: 3 July 2009 / Revised: 22 September 2009 / Accepted: 29 September 2009 / Published: 26 October 2009
(This article belongs to the Special Issue Laser Spectroscopy and Sensing)
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We discuss the detection limit for refractometric sensors relying on high-Q optical cavities and show that the ultimate classical detection limit is given by min {Δn} ≳ η with n + iη being the complex refractive index of the material under refractometric investigation. Taking finite Q factors and filling fractions into account, the detection limit declines. As an example we discuss the fundamental limits of silicon-based high-Q resonators, such as photonic crystal resonators, for sensing in a bio-liquid environment, such as a water buffer. In the transparency window (λ ≳ 1100 nm) of silicon the detection limit becomes almost independent on the filling fraction, while in the visible, the detection limit depends strongly on the filling fraction because the silicon absorbs strongly.
Keywords: refractometry; resonators; optofluidics; photonic crystals refractometry; resonators; optofluidics; photonic crystals
This is an open access article distributed under the Creative Commons Attribution License (CC BY) which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

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Skafte-Pedersen, P.; Nunes, P.S.; Xiao, S.; Mortensen, N.A. Material Limitations on the Detection Limit in Refractometry. Sensors 2009, 9, 8382-8390.

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