A current collector wire (1) is over-moulded with a seal (2) made from a thermoplastic elastomer (Santoprene 64) having a (64) Shore A hardness rating. In a three electrode carbon monoxide sensor three current collector wire (1a, 1b, 1c) and seal (2a, 2b, 2c) combinations are inserted into the body (3) through receiving apertures (12a, 12b, 12c) in a side wall of the body, so that the current collectors protrude through connection apertures (12a, 12b and 12c). The outside diameters of the seals and the bores of the apertures are dimensioned to provide an interference fit of the one in the other. The seals are pressed home into receiving apertures in the body (3) to provide compression of the seals against both current collectors and the aperture bores resultant from the interference. Gold-plated phosphor bronze clips (8) are attached which locate on and are retained by barbs on the housing, thereby trapping the current collector wires and providing electrical contact to external circuitry.