Is there something inherently hard about producing such a sensor say as a pressure or temperature sensor or is it patented and we're all screwed because of that?
Thanks!
A DIY sensor needs to either be some kind of test strip or a needle. Both are a lot easier to just get through insurance than to mimic.
I'm sure you could perform the chemical reactions yourself, but you'll probably find whatever you make will need to be replaced frequently. Meanwhile, the software, modified Android phones, etc. last a long longer, so that's where is the action.
Some people write bespoke apps for their data, but that's obviously not typical.
The challenge for the homebrewer is to build something traceable. When you measure blood sugar today the same sample should yield the same number - not only today but also ten years from now. Yes, Theranos is fighting with traceability, too.