Every time I get one of those little finger cuff blood gas analyzers on my finger I'm reminded of this idea I had back in the mid 80's. A couple of the engineers at Essex Magnet Wire were testing IR pyrometers to measure the temperature of molten copper. They discovered that the oxygen content of the molten metal influenced the emissivity adjustment of the instruments and concluded that they were not of much use. I on the other hand saw a potential way to measure the oxygen in the molten metal.
Note: Essex had been sacrificing about an engineer a year to the molten metal oxygen sensor god without getting any closer to finding the perfect oxygen sensor that would not be consumed by the molten metal it was trying to measure.
I thought they would be delighted. Alas they were not interested and imagine my dismay when a few years later, a doctor looking for a less intrusive way to measure blood gasses stumbled onto a similar use for infrared light. Obviously he was much more successful with his inventing than I was.