“Click-assembly” methods of assembling a sensor for sensing biologically-active molecules by measuring impedance changes, are disclosed, comprising supporting a bio-sensor on a carrier, the bio-sensor comprising an electronic component having at least one micro-electrode and at least one electrical contact, functionalizing the bio-sensor by physically or chemically coupling a bio-receptor molecule to each of the at least one micro-electrode, and subsequently assembling the bio-sensor with a micro-fluidic unit by means of a clamp which clamps the bio-sensor with the micro-fluidic unit, such that in use a fluid introduced into the micro-fluidic unit is able to contact the bio-receptor and is isolated from the electrical contact. The clamp may be a spring, and the method may avoid a requirement for sealing by chemical or thermal means and thereby avoid damaging the bio-receptor.Sensors which can be assembled according to such methods are also disclosed.