• A wireless and portable optical biosensor reader is developed to detect the concentration of ammonium at site.
• The reader uses glutamate dehydrogenase (GLDH) and diaphorase (Dph) enzyme as biosensors that respond to the presence of ammonium upon exposure to light.
• The absorption of light depends on the concentration of ammonium compounds. The reader measures the light intensity, performs signal processing and displays the result on any android based smartphone via bluetooth communication.