Anyway, this problem, to measure blood glucose non-invasive, is solved now. A product should be on the market very soon. And while I am not involved anymore, I once submitted an SBIR grant application to the NIH with this technology. A specific item that this technology used would be a few hundreds bucks if produced in quantities. I also wrote this in the grant application. The examiner googled this thing, and a top-notch single item for lab measurements was 50 grand. Obviously, too expensive. So the thing I learned:
An idiot and Google are a very dangerous combination. Even at the NIH.
PS: Neither the start-up, nor their technology is mentioned in the paper. All the mentioned technologies have been tried and are bound to fail in my opinion. At least the examiner gave me a very high score on "innovative".