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Towards ultrasound enhanced mid-IR spectroscopy for sensing bacteria in aqueous solutions
Author(s): Stephan Freitag; Andreas Schwaighofer; Stefan Radel; Bernhard Lendl
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Paper Abstract

We employ attenuated total reflection (ATR) mid-IR technology for sensing of bacteria present in aqueous solution. In ATR spectroscopy, the penetration depth of the evanescent field extends to approx. 1-2 micrometers into the aqueous solution depending on the refractive index of the employed materials (Si, ZnS, Ge) used as attenuated total reflection (ATR) element and the geometry of the optical set-up. Due to the flow profile in the microfluidic cell, an additional force is required to bring particles into the evanescent field for measurement. For that purpose, we employ standing ultrasound waves produced between a sound source vibrating at approx. 2 MHz and the ATR crystal acting as a reflector. This ultrasonic trap is integrated into the microfluidic channel. As aqueous solution is passing through that acoustofluidic cell, particles are concentrated in the nodal plane of the standing ultrasound wave, forming particle conglomerates. By selecting appropriate experimental conditions, it is then possible to press bacteria against the crystal surface for interaction with the evanescent wave (as well as to keep them away from the ATR element). Our current work aims at establishing a custommade US-ATR-IR setup for signal enhancement of bacteria (e.g. E. coli, P. aeruginosa as well as Salmonella) in drinking water.

Paper Details

Date Published: 19 February 2018
PDF: 6 pages
Proc. SPIE 10491, Microfluidics, BioMEMS, and Medical Microsystems XVI, 104910M (19 February 2018); doi: 10.1117/12.2290390
Show Author Affiliations
Stephan Freitag, Technische Univ. Wien (Austria)
Andreas Schwaighofer, Technische Univ. Wien (Austria)
Stefan Radel, Technische Univ. Wien (Austria)
Bernhard Lendl, Technische Univ. Wien (Austria)


Published in SPIE Proceedings Vol. 10491:
Microfluidics, BioMEMS, and Medical Microsystems XVI
Bonnie L. Gray; Holger Becker, Editor(s)

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