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M. Brandstetter, B. Lendl:
"Tunable mid-IR lasers: A new avenue to robust and versatile physical chemosensors for bodily fluids";
Talk: SPEC 2010 Shedding Light on Disease: Optical Diagnosis for the new Milleninum, Manchester; 06-26-2010 - 07-01-2010; in: "SPEC 2010 Shedding Light on Disease: Optical Diagnosis for the New Millenium", (2010), 110.

A novel approach for a physical chemosensor for bodily fluids based on mid-infrared Quantum Cascades Lasers (QCL) is presented. Since their first demonstration in 1994, QCLs have been constantly improved and have now reached spectral power densities up to several hundreds of mW within one wavenumber. Due to their small size and room temperature operation they hold promise to revolutionize the way IR measurements are carried out. An interesting field of application of these lasers are measurements of aqueous solutions where, for the first time, measurements through optical paths of larger than 150 µm can be achieved. This is a significant improvement in terms of robustness of the measurement set-up, especially when samples containing cells or other particles are to be analyzed.
Here we report on the use of a room-temperature operated pulsed External-Cavity (EC) QCL, tuneable from 1030 -1230 cm-1, for transmission measurements of physiological solutions using path lengths of over 150 µm. For detection a thermoelectrically cooled MCT detector was used. The achieved signal-to-noise ratios compete with those obtainable on state-of-the-art FT-IR spectrometers. The broad tuning range furthermore permits multi-analyte detection based on multivariate calibrations. Results on simultaneous determination of glucose and lactate in aqueous solutions are reported (Fig. 1). The experimental findings obtained so far clearly indicate that the presented concept of using room temperature mid-IR EC-QCL in combination with thermoelectrically cooled MCT detectors holds promise for constructing small, portable and robust sensor systems for measuring bodily fluids such as blood and urine.