Since quite some time, the Austrian biomedical research and development company AVL List GmbH has been focusing on the production of opto-chemical sensors. At present, AVL is selling a portable optical blood gas analyser, called OPTI 1, based on fluorescence intensity. Yet, AVL researcher Paul Hartmann recently has designed and tested within the Esprit funded QUANTUM project an imaging oxygen sensor based on luminescence lifetime or decay measurements. This new approach offers the possibility of non-invasive, quantitative and calibration-free imaging of the skin 'respiration'. The method may play an important role in the diagnosis of chronic venous insufficiency, ulcerations, wound healing, burns, amputations, micro-circulatory disturbances and the effects of drugs for improvement of circulation.
Measuring oxygen levels within living cells, tissue or an entire organism helps the physician to form a sound diagnosis on the viability of the patient's skin. Hitherto established methods such as the widely used electrodes suffer from oxygen consumption, dependence on oxygen transport conditions and interference of electromagnetic fields which leads to less reliable results.
The lifetime-based oxygen sensor, on the contrary, works on the principle that the luminescence intensity and decay time of certain dyes are quenched by molecular oxygen. The luminescence decay time is an average time a dye molecule persists in its excited state. After forming a sensing layer of polymer containing a ruthenium complex onto a polyester sheet for support, this is covered by a black optical isolation layer to keep out stray light. To excite the luminescence in the sensing layer, Hartmann and his colleagues combine eight superbright blue light emitting diodes (LEDs) which are pulsed on and off rapidly. A charge-coupled device (CCD) camera records the emission monitoring the decay between light pulses in order to transfer the data to a personal computer.
The imaging oxygen sensor outperforms all existing devices because of its accurate measurements but still has one great disadvantage, according to Hartmann. This optical technique requires a polymer sensor to come in close contact with the patient's skin which causes problems on wet skin or open wounds. Nevertheless, the use of luminescence spectroscopy holds the advantages of optical sensing without losing the accuracy and reproducibility which were responsible for the popularity of electro-chemical techniques in the past. AVL applies inexpensive yet robust instrumentation with additional provision of oxygen level images. Please contact Dr. Paul Hartmann