A method of fabricating an array of plasmonic structures, a biosensor and a method of fabricating the biosensor. The biosensor includes: an array of plasmonic structures arranged on a base, and defining a detection surface distanced from the base; a separator arranged to separate at least a main portion of a cell from the detection surface; wherein the biosensor is arranged to detect, based on a change of an optical property of the array of plasmonic structures, in response to one or more protrusions extending from the main portion of the cell reaching the detection surface.