the invention provides a method for detection of receptor - or ion channel - modulators . the method comprises fractionating a sample by using a liquid - based separation means , and feeding the fractions containing the modulators directly to a biosensor . the biosensor is activatable by a receptor agonist and produces a measurable response as a result of this activation . preferably , the agonist is fed to the biosensor through the liquid - based separation means , together with fractions containing the modulators . the presence of a modulator is detected by monitoring a change in the response of the biosensor , e . g ., by measuring changes in electrical properties of the biosensor . in one aspect , the biosensor is periodically resensitized by delivering pulses of receptor agonist to the biosensor for short period of time which are separated by other periods when no agonist is delivered to the biosensor . the invention further provides a system for performing the method . the system facilitates sequential patch clamp recordings of cell - based biosensors .