I wrote previously about a technology being developed at MIT that uses infra-red light to detect blood glucose. Now, Northeastern University is working on a technology that binds nanoparticles to a target chemical when injected into the skin. They can then use LED light and an iPhone to read the nanoparticles when they fluoresce. The amount of fluorescence can be analyzed and translated into a measurement of the level of the target chemical. And recently receiving CE approval and now on the market is the Veralight Scout DS system, which also uses light to detect fluorescence in the skin to screen for type 2 diabetes.
I believe that for testing and diagnostic products, medical device design will be incorporating light technologies to usher in a revolution in non-invasive detection.