A disposable device is described for use in High Content Screening within the drug research process; it interfaces with a standard 384 well microtiter plate providing simultaneous full kinetic reaction data for a complete row of 24 wells. The device can be used in secondary screening for lead optimisation, for ADME (Absorption Distribution Metabolism and Excretion) assessment and toxicological assessment of candidate compounds. The device is a microfluidic unit and incorporates the necessary substrate and reaction chemicals. The microfluidic circuitry includes mixing paths, a reaction chamber, a single use valve and a waste reservoir as well as electrical measurement contacts. Movement of the fluids is provided by a single vacuum line which is distributed to all 24 separate cells. The device described incorporates a self-validation technique which provides a built in test facility.