The present invention provides a sensor, such as a biosensor, comprising at least one self-assembled monolayer (SAM) comprising analyte-sensitive groups, such as glucose-sensitive groups, attached to the surface of the outer wall of a carbon nanotube (CNT), such as a single-walled carbon nanotube (SWNT), by terminal groups, which bind to a thin layer of a metal or metal oxide, which has been deposited on the surface of the outer wall of the nanotube.