Diabetes mellitus is a disorder of glucose metabolism and it is one of the most challenging diseases, both from a
medical and economic perspective. People with diabetes can benefit from a frequent or even continuous monitoring
of their blood glucose concentrations. The approach presented here takes advantage of the observational
nature of biomedical vibrational spectroscopy in contrast to chemical reactions which consume glucose. The
particular technique employed here is based on the high sensitivity of mid-infrared transmission spectroscopy
where strong vibrational bands of glucose can be monitored at wavelengths around 10 μm. The strong absorption
of water in this spectral region was mitigated by the use of quantum cascade lasers and very short interaction
path lengths below 50 μm. Various sensor concepts have been explored. In one of the concepts, the interaction
of mid-infrared radiation with glucose is established within a miniature measurement cavity, formed by a gap
between two silver halide fibers. In recent experiments, an additional quantum cascade laser was used for reference
purposes. The long-term drift could significantly be reduced for time intervals > 1000 s, e. g., by more than
60% for a 3 hour interval. This extension for the compensation of long-term drifts of the measurement system
in vitro is an important contribution towards the applicability in vivo.
The continuous monitoring of the concentration of glucose provides an essential tool for the improved glycemic
control for people with diabetes. Most of the present approaches of transcutaneous, continuous glucose monitors
are based on chemical detection and require the insertion of reagents into the body. In contrast, we aim at the
reagent-free monitoring of glucose by means of mid-infrared spectroscopy.
A quantum cascade laser provides narrow band radiation at wavelengths around the absorption bands of glucose
(≈ 10 μm). At the same time it yields sufficient energy to allow for a good signal-to-noise ratio in transmission
measurements despite the strong background absorption of water.
We investigated various concepts for the sensor head based on the light-guiding properties and handling of
materials such as AgCl/AgBr or silicon. In-vitro experiments were performed using a custom-made, temperaturestabilized
measurement flow chamber. In preparation for future in-vivo applications first results of biotoxicity
tests of the fiber sensors are given.
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