Several centuries ago, but not as many as you would think, doctors sniffed the patient to detect tell-tales of an ailment. And this went on till the first part of last century when the sniffing was displaced by a (growing) variety of clinical exams.
Now, may be, we will go back to the sniffing procedure, although now the sniffing will be done by a sensor coupled to a computer.
SERS has been available for several years but the problem with it is the difficulty in getting stable results. Here is where Optokey solution comes in. They have coupled SERS to a nano-plasmonic resonator (plasmonic is a particular status of electrons at the surface of a material that interact with photons) and have managed to produce at industrial level these resonators on a wafer making them economically affordable.
The micro sensors can detect single molecules and doctors know that some molecules are specific indicators for certain diseases or even certain microbe. Using this kind of sensor in your kitchen you would be able to detect if there is some nasty microbes in the milk you left out of the fridge for a day.
Our nose detects molecules and convey signals that our brain converts into "odours". It is pretty good, although not as good as our dog's nose (a dog has a sense of smell that is 1,000 to 10 million times better than our, a dog's nose contains 125-300 million sensing cells whilst our nose has to live with 5 millions...). This micro-sensor is better than a dog's nose although its sensitivity has to be turned into an "understanding" by a computer that will process the signals generated by the artificial nose. In the end, hard technology is the enabler but making sense of it requires computation...