Still, the quest for non-invasive glucose monitoring continues to captivate scientists and investors. A slew of startups and several large companies, including Apple, are working on various approaches to solving the puzzle.

Berlin-based Quantune Technologies may have made some progress: Its founders, Dr. Jan Kischkat (pictured above at the far right) and Nikolaus Hahne (pictured above, second from right), said they have succeeded in reducing the size of an infrared laser spectrometer to a much smaller size. Laser spectrometers are normally bulky devices that can measure glucose and other molecules non-invasively in interstitial fluid, which nourishes all the cells and is present right below the skin, Kischkat explained.