Autonomous, WirelessIn-SituSensor (AWISS) for Rapid Warning ofEscherichia coliOutbreaks in Recreational and Source Waters

Abstract

An autonomous, wireless, in-situ sensor (AWISS) was demonstrated for the detection of Escherichia coli. A prototype battery-powered optical AWISS, consisting of a miniature spectrophotometer, monitored the changes in fluorescence intensity that occur when the E. coli–synthesized β-glucuronidase enzyme hydrolyzes the reagent's glycosidic bond, releasing fluorophores into solution. Laboratory testing with the prototype sensor showed the AWISS was capable of detecting low concentrations (<100 colony forming units [CFU]/100 mL) in less than eight hours. Higher concentrations (>5000 CFU/100 mL), indicative of a possible combined sewage discharge, could be detected in under one hour. A seven-day demonstration utilized the prototype sensor to sample and record the bacterial water quality of the St. Joseph River in South Bend, Indiana. Every six hours a new sample was drawn into a custom-designed stop-flow reaction chamber and injected with a soluble reagent. A wireless transmitter sent intensity data to a remote monitoring station. The deployment produced 19 individual sampling events, of which 15 were compared to culture methods approved by the U.S. Environmental Protection Agency (USEPA). Four samples were drawn in the middle of the night and not verified. Of the 15 verified samples, 13 correctly identified the presence or absence of an E. coli concentration defined as significant by the USEPA and Indiana Department of Environmental Management (IDEM) thresholds of 125 CFU/100 mL.