Devices like these are there for decades. However, our ability to identify molecules that could be targeted and would be able to give us definitive answers- aren't. Sometimes when it is known patient has cancer, but biopsy is not preferable or possible, blood tests for circulating cells, circulating tumor DNA are performed. This does not work well with specific tumors that don't normally leak into blood.

Sorry for long one. Basically, there's still long way to go when it comes to using something like this for detection.