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M. Brandstetter, A. Genner, T. Sumalowitsch, E. Aguilera-Herrador, V. Fuhrmann, T. Perkmann, C. Jungbauer, B. Lendl:
"Tunable Quantum Cascade Laser based sensor for point-of-care blood analysis";
Vortrag: SPEC 2012 - Shedding New Light on Disease, Chiang Mai, Thailand (eingeladen); 11.11.2012 - 16.11.2012; in: "SPEC 2012", (2012), 1 S.

Fast and reagent-free point of care blood analysis is of increasing interest in clinical medicine and of particular interest in intensiv care medicine. Mid-infrared (MIR) spectroscopy using Quantum Cascade Lasers (QCL) in combination with fundamental multivariate data analysis is a promising candidate to fulfill this task.
In our study we applied a broadly tunable External Cavity QCL (EC-QCL) with a spectral tuning range from 1030 cm-1 to 1230 cm-1. This type of QCL can cover several of the broad and overlapping analyte absorption bands typical for measurements in liquids. Furthermore, peak power levels of several hundreds of mW are achievable, if operated in pulsed-mode. Given this high optical power a portable sensor set-up with a large optical pathlength transmission flow cell (165 μm) could be realized preventing clogging of the flow cell. A robust single-channel set-up was realized avoiding additional optical parts, such as etalons or beam modulators. Experimental practice revealed, however, that the spectral performance of pulsed mode EC-QCLs is limited. Therefore, a correction algorithm was developed and applied. Laser instabilities were, e.g., corrected by making use of the inherent structure of the EC-QCL´s gain curve [1].
The portable sensor system was first applied to aqueous solutions [2, 3]. Subsequently, more than 150 routinely taken blood samples including blood serum from healthy donors [4] and blood plasma from critically ill patients were analyzed. Using multivariate data analysis a range of blood parameters could simultaneously be quantified in their relevant concentration ranges, among them glucose (c= 40-380 mg/dl), triglycerides (c= 40-460 mg/dl), total protein (c= 35-70 g/l) and albumin (c= 17-35 g/l). Fibrinogen, a clotting factor contained in blood plasma, could be quantified as well (c= 250-800 mg/dl).
Additionally, as an outlook for a potential future application of the EC-QCL sensor, preliminary data on the determination of blood groups using Attenuated Total Reflection (ATR) FTIR spectroscopy are presented.

Quantum Cascade Laser, Glucose, Albumin, Fibrinogen, Blood