A device and method for detecting and/or measuring a polysaccharide-hydrolysing activity of an enzyme and/or quantifying the amount of the enzyme in a sample employs a complex of a polysaccharide that is hydrolysable by the enzyme and an electrically active signal species or progenitor thereof such that action of the enzyme on the complex causes liberation of the signal species or progenitor.  Thus enzyme activity leads to free signal species which can be detected and quantified electrically.