title: In-a-day electrochemical detection of coliforms in drinking water using a tyrosinase composite biosensor.
abstract: A rapid method for the detection of fecal contamination in water based on the use of a tyrosinase composite biosensor for improved amperometric detection of beta-galactosidase activity is reported. The method relies on the detection of phenol released after the hydrolysis of phenyl beta-D-galactopyranoside (PG) by beta-galactosidase. Under the optimized PG concentration and pH (4.0) values, a detection limit of 1.2x10(-3) unit of beta-galactosidase/mL-1 was obtained. The capability of the sensor for the detection of Escherichia coli was evaluated using polymyxin B sulfate to allow permeabilization of the bacteria membrane. A detection limit of 1x10(6) cfu of E. coli mL-1 was obtained with no preconcentration or pre-enrichment steps. To improve the analytical characteristics for bacteria detection, the processes involving galactosidase induction during incubation and membrane permeabilization were optimized. Using 0.25 mM isopropyl beta-D-thiogalactopyranoside for the enzyme activity induction, and 10 microg mL-1 polymyxin B sulfate as permeabilizer agent, it was possible to detect bacteria concentrations as low as 10 cfu mL-1 after 5 h of enrichment. The possibility of detecting E. coli at the required levels for drinking water quality assessment (1 cfu/100 mL) is demonstrated, the time of analysis being shorter than 6.5 h and involving a simple methodology.
authors.affiliation: Department of Analytical Chemistry, Faculty of Chemistry, Complutense University of Madrid, Avenida Complutense s/n 28040 Madrid, Spain.
authors.forename: Beatriz
authors.initials: B
authors.lastname: Serra
authors.forename: M Dolores
authors.initials: MD
authors.lastname: Morales
authors.forename: Jinbiao
authors.initials: J
authors.lastname: Zhang
authors.forename: A Julio
authors.initials: AJ
authors.lastname: Reviejo
authors.forename: Elizabeth H
authors.initials: EH
authors.lastname: Hall
authors.forename: Jose M
authors.initials: JM
authors.lastname: Pingarron
mesh_terms: D015374:Biosensing Techniques / Q000379:methods*; D004755:Enterobacteriaceae / Q000302:isolation & purification*; D004790:Enzyme Induction; D004926:Escherichia coli / Q000302:isolation & purification / Q000378:metabolism; D007544:Isopropyl Thiogalactoside / Q000494:pharmacology; D014442:Monophenol Monooxygenase / Q000378:metabolism*; D014871:Water Microbiology; D014881:Water Supply / Q000592:standards; D001616:beta-Galactosidase / Q000096:biosynthesis
chemical_list: D007544:Isopropyl Thiogalactoside; D014442:Monophenol Monooxygenase; D001616:beta-Galactosidase