title: Colorimetric enumeration of bacterial contamination in water based on β-galactosidase gold nanoshell activity.
abstract: In this study we report a method for the rapid and sensitive estimation of bacterial cell concentration in solution based on a colorimetric enzyme/gold nanoshells conjugate system. The CTAB capped gold nanoshells are electrostatically attracted by both the bacterial surface and the enzyme β-galactosidase. The preferential binding of cationic (CTAB)-functionalized gold nanoshells to the more negative bacterial surfaces leaves active β-galactosidase in solution, providing an enzyme-amplified colorimetric response of the binding event. A progressive increase in the enzyme activity is evidenced by the conversion of the yellow-orange CPRG substrate into the red chromophore chlorophenol red, which can be correlated with increasing bacterial cell numbers. Using this strategy, the quantification of bacteria at concentrations as low as 10 bacteria/mL of solution has been achieved. The present method of bacterial cell load assessment offers a distinct potential advantage over other conventional methods such as plate counting in terms of ease of operation, rapidity, high sensitivity and quantitative detection of bacterial cells.
authors.affiliation: Department of Zoology, Government College University, Lahore, Pakistan; Department of Chemical Engineering, University of Waterloo, Waterloo, ON, Canada.
authors.forename: Fouzia
authors.initials: F
authors.lastname: Tanvir
authors.affiliation: Department of Zoology, Government College University, Lahore, Pakistan.
authors.forename: Atif
authors.initials: A
authors.lastname: Yaqub
authors.affiliation: Department of Chemical Engineering, University of Waterloo, Waterloo, ON, Canada.
authors.forename: Shazia
authors.initials: S
authors.lastname: Tanvir
authors.affiliation: Department of Chemical Engineering, University of Waterloo, Waterloo, ON, Canada. Electronic address: wanderson@uwaterloo.ca.
authors.forename: William A
authors.initials: WA
authors.lastname: Anderson
mesh_terms: D001419:Bacteria / Q000302:isolation & purification / Q000472:pathogenicity; D058491:Bacterial Load / Q000379:methods*; D000077286:Cetrimonium; D002593:Cetrimonium Compounds; D003124:Colorimetry / Q000379:methods*; D060766:Drinking Water / Q000382:microbiology*; D006046:Gold; D006801:Humans; D046529:Microscopy, Electron, Transmission; D057145:Nanoshells / Q000737:chemistry / Q000648:ultrastructure; D036103:Nanotechnology; D014871:Water Microbiology; D001616:beta-Galactosidase
chemical_list: D002593:Cetrimonium Compounds; D060766:Drinking Water; D006046:Gold; D001616:beta-Galactosidase; D000077286:Cetrimonium
keywords: Bacterial enumeration; Colorimetric assay; Gold nanoshells; Nanocomposite; β-galactosidase