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Mid-IR sensing platform for trace analysis in aqueous solutions based on a germanium-on-silicon waveguide chip with a mesoporous silica coating for analyte enrichment

: Teigell Benéitez, Nuria; Baumgartner, Bettina; Missinne, Jeroen; Radosavlkevic, Sanja; Wacht, Dominik; Hugger, Stefan; Leszcz, Pawel; Lendl, Bernard; Roelkens, Gunther

Volltext urn:nbn:de:0011-n-6032014 (2.0 MByte PDF)
MD5 Fingerprint: b840d3664a99a15490c96e11cf8a4c7b
Erstellt am: 1.10.2020

Optics Express 28 (2020), Nr.18, S.27013-27027
ISSN: 1094-4087
Zeitschriftenaufsatz, Elektronische Publikation
Fraunhofer IAF ()

A novel platform based on evanescent wave sensing in the 6.5 to 7.5 µm wavelength range is presented with the example of toluene detection in an aqueous solution. The overall sensing platform consists of a germanium-on-silicon waveguide with a functionalized mesoporoussilica cladding and integrated microlenses for alignment-tolerant back-side optical interfacing with a tunable laser spectrometer. Hydrophobic functionalization of the mesoporous cladding allows enrichment of a polar analyte molecules and prevents strong interaction of water with the evanescent wave. The sensing performance was evaluated for aqueous toluene standards resulting in a limit of detection of 7 ppm. Recorded adsorption/desorption profiles followed Freundlich adsorption isotherms with rapid equilibration and resulting sensor response times of a few seconds. This indicates that continuous monitoring of contaminants in water is possible. A significant increase in LOD can be expected by likely improvements to the spectrometer noisefloor which, expressed as a relative standard deviation of 100% lines, is currently in the range of 10⁻² A.U.