An impedance sensor comprising a front-end circuit and two electrodes (3a,b), whereby one of the two electrodes is connected to a first input-terminal and the other of the two electrodes is connected to a second input-terminal whereby the front-end circuit is arranged in a sensor head and the two electrodes (3a,b) are arranged in a sensor body and whereby the sensor head is mounted to the sensor body and whereby the front-end circuit comprises a. the first and the second input-terminal (13a,b); b. an excitation-terminal for receiving an excitation signal relative to a common ground; c. an operational amplifier comprising i. an inverting input and ii. an Op-Amp output; whereby d. the front-end circuit comprises a switching unit e. and a state of the switching unit (15a,b) determines an operation of the operational amplifier, such that i. in the case of the use of the front-end circuit, during which electrodes are connected to the first and the second input terminal while a sample is arranged between the electrodes and while an excitation signal is received at the excitation-terminal, ii. the excitation signal controls, depending on the state of the switching unit, either a current flowing through the electrodes and the sample or a voltage across the electrodes and the sample. whereby the front-end circuit is arranged in a sensor head and the two electrodes (3a,b) are arranged in a sensor body and whereby the sensor head is mounted to the sensor body and whereby the front-end circuit comprises a. the first and the second input-terminal (13a,b); b. an excitation-terminal for receiving an excitation signal relative to a common ground; c. an operational amplifier comprising i. an inverting input and ii. an Op-Amp output; whereby d. the front-end circuit comprises a switching unit e. and a state of the switching unit (15a,b) determines an operation of the operational amplifier, such that i. in the case of the use of the front-end circuit, during which electrodes are connected to the first and the second input terminal while a sample is arranged between the electrodes and while an excitation signal is received at the excitation-terminal, ii. the excitation signal controls, depending on the state of the switching unit, either a current flowing through the electrodes and the sample or a voltage across the electrodes and the sample. a. the first and the second input-terminal (13a,b); b. an excitation-terminal for receiving an excitation signal relative to a common ground; c. an operational amplifier comprising i. an inverting input and ii. an Op-Amp output; whereby i. an inverting input and ii. an Op-Amp output; d. the front-end circuit comprises a switching unit e. and a state of the switching unit (15a,b) determines an operation of the operational amplifier, such that i. in the case of the use of the front-end circuit, during which electrodes are connected to the first and the second input terminal while a sample is arranged between the electrodes and while an excitation signal is received at the excitation-terminal, ii. the excitation signal controls, depending on the state of the switching unit, either a current flowing through the electrodes and the sample or a voltage across the electrodes and the sample. i. in the case of the use of the front-end circuit, during which electrodes are connected to the first and the second input terminal while a sample is arranged between the electrodes and while an excitation signal is received at the excitation-terminal, ii. the excitation signal controls, depending on the state of the switching unit, either a current flowing through the electrodes and the sample or a voltage across the electrodes and the sample.