Abstract: A molecular sensor (10) comprises a flow path (12) configured for flowing a solution (28) potentially containing a target molecule (26). A source of polarised light (16) is provided and a detector (18) arranged to receive light from the source after it has passed through the flow path. A sensor element (19) is provided comprising a scaffold moiety (20) with a high aspect ratio disposed, in use, within the flow path and a receptor moiety (24), for the target molecule, attached to the scaffold moiety. A method for sensing a target molecule in a flowing solution is also described.