The present application relates to sensors and methods for detecting and/or quantifying an oxidant such as free chlorine in a liquid sample such as drinking water. The sensors comprise a first electrode, a second electrode and a composite material between and connecting the first electrode and the second electrode, the composite material comprising a semiconductor and a redox-switchable organic compound associated therewith. The methods comprise exposing the liquid sample to the sensor under conditions to oxide the redox-switchable organic compound and analyzing a resulting change in current.
