[Zurück]

S. Radel, J. Schnöller, E. Benes, B. Lendl:
"Ultrasonic standing wave accelerates on-line measurement and prevents coating of a FTIR ATR flow cell";
in: "Proc. IEEE Sensors 2004", D. Rocha, P.M. Sarro, M. Vellekoop (Hrg.); IEEE, 2004, S. 757 - 759.

It has been shown elsewhere that infrared (IR) spectroscopy
can be successfully employed for the on-line monitoring
of bio-processes. A horizontal attenuated total reflection
(ATR) unit connected to a portable IR-cube was
used here to measure the IR absorption spectra of supernatant
and microorganism separately. The common problem
of bio-film formation on the ATR was addressed before,
e.g. by chemical means. We present a novel method employing
the principles of ultrasonic particle manipulation
to avoid and potentially remove this coating brought about
by the use of fermentation broth.
A novel flow cell for a horizontal ATR was developed that
decreases measurement time and the undesired formation
of bio-films on the ATR surface. An ultrasonic standing
wave (~2MHz) is build up between a horizontal transducer
and the ATR crystal. Yeast cells in suspension were agglomerated
within certain regions by the ultrasound field
and therefore settled about 3-4 times faster on the ATR
when the field was switched off compared to the slow sedimentation
of freely dispersed cells. After the IR spectrum
had been measured, the same sound field was used to actively
lift the settled material from the optical sensitive surface
which therefore could be rinsed away more effectively.

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