text: Electrochemical impedance spectroscopy (EIS) involves measuring resistive and capacitive changes caused by a biorecognition event. Typically, a small amplitude sinusoidal electrical stimulus is applied, causing current to flow through the biosensor. The frequency is varied over a range to obtain the impedance spectrum. The resistive and capacitive components of impedance are determined from in phase and out of phase current responses. Typically, a conventional three-electrode system is made specific to the analyte by immobilizing a biorecognition element to the surface. A voltage is applied and the current is measured. The interfacial impedance between the electrode and solution changes as a result of the analyte binding. An impedance analyzer can be used to control and apply the stimulus as well as measure the impedance changes.