Enhanced Surface-to-Bulk Sensitivity Ratio of a
Waveguide Grating Biosensor
by Angular Interrogation at Short Wavelengths

F. Kehl^1,2,3, S. Follonier², J. Vörös³

¹Optics Balzers AG, Liechtenstein, ²CSEM Landquart, Switzerland,
³Laboratory of Biosensors and Bioelectronics LBB, ETH Zürich, Switzerland

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Results in brief

Label-free waveguide grating based biosensors are highly sensitive to effective refractive index changes caused by the adsorption of biomolecules onto the sensor surface and/or due to refractive index changes of the bulk solution¹. As these changes can only be sensed within the penetration depth of the evanescent field of the propagating mode, the so-called surface-to-bulk sensitivity ratio can be optimized by changing the wavelength of the interrogating light source. Since short wavelengths lead to a shallower penetration into the bulk solution but higher field densities in close proximity to the sensor, events of molecular binding to the surface can be measured with enhanced sensitivity, whereas adverse refractive index changes of the bulk solution are suppressed^2,3. And the higher refractive index contrast at shorter wavelengths leads to an increased sensitivity. Besides numerical simulations and comparative measurements at different interrogation wavelengths ranging from the near-ultraviolet to the infrared, an integrated angle interrogated micro-electro-mechanical sensor system working at shorter wavelengths and higher repetition rates than common commercial systems has been presented.

The presented work is part of the FP7 Project RADAR, funded by the European Commission, Grant Agreement Number 265721, a project which aims to develop a multiplex robust, labelfree, remotely controlled, and portable biosensor platform for spot measurements and online monitoring of toxins and pollutants in food production processes and in the aquatic environment.