Devices and methods that measure one or more properties of a living cell culture that is contained in liquid media within a vessel, and typically analyzes plural cell cultures contained in plural vessels such as the wells of a multiwell microplate substantially in parallel. The devices incorporate a sensor that remains in equilibrium with, e.g., remains submerged within, the liquid cell media during the performance of a measurement and during addition of one or more cell affecting fluids such as solutions of potential drug compounds.