Not my area of expertise, but I'm a type 1 diabetic and that area seems ripe for improvement. Artificial pancreases, automatic glucose monitoring and the like are an area that is exploding.
A while back I read about a method that used a very small bioactive fluorescent dye tattoo, and a light sensor to measure glucose levels. It's not continuous, but it's painless (after the tattoo), can be done often, and is much less expensive than existing continuous glucose monitoring devices.
Another article I read described some Google research that involved an instrumented contact lens that measured glucose levels by measuring something in tears and sending the results using near field communications to a monitor device. This device provides continuous monitoring, (no tattoo required), and I am guessing that total cost would be less than existing CGM devices.
I haven't heard anything about these research efforts lately, and if they're still being worked on, it could be years more before they become available.