Detection of trace amounts of arsenic in laboratory solutions can be readily achieved by inductively coupled plasma mass spectrometry (ICP-MS). This is a very sensitive method with a limit of detection (LOD) in the nanomolar range [9–11]. However, such a method is expensive and not appropriate for field detection. Accordingly, there is an increasing need for a portable and sensitive sensor to be developed which gives reliable measurements for the detection of arsenic at low concentrations.