Later on, Roche Diagnostics happened to be pondering the question
‘Wouldn’t it be useful to have a non-electrical version of the ion
selective electrode?’ especially for use in critical care wards where
the patients are monitored by a bank of electrical monitors. A device
with a non-electrical front end is less likely to suffer cross-talk.
Again, fluorescent PET sensors turned out to be a satisfactory answer
since they have an optical front end \cite{optimedicalcom}. Now these
fluorescent PET sensors are seeing use in ambulances so that blood
sodium levels can be determined in seconds at the scene of an injury.
What is good for a human is also good for other animals. So it is no
surprise that fluorescent PET sensors are also seeing use in veterinary
situations \cite{idexxcom}.