An impedimetric sensor is based on the EIS technique and measures the resistive or capacitive behaviour of an electrochemical system. EIS investigates the AC current response to an AC potential in respect to frequency, ƒ. A sinusoidal potential is applied to the system and the responding sinusoidal current is measured over a range of frequencies. These sinusoidal responses are at the same frequency but out of phase (φ) with each other. The excitation voltage can be expressed as a function of time: (1) where E t is the potential at time t, E 0 is the signal amplitude and ω is the angular frequency. The relationship between frequencies ω (rad s -1 ) and ƒ (Hz) is: (2) The responding current can also be expressed as a function of time: (3) where I t is the current at time t, I 0 is the signal amplitude and φ is the phase shift. A corresponding version of Ohm's law can be used to describe AC impedance: (4) This frequency-dependent impedance is expressed in terms of a magnitude, Z 0 , and phase shift.