Demonstration of Tryptophan-Like Fluorescence Sensor Concepts for Fecal Exposure Detection in Drinking Water in Remote and Resource Constrained Settings

Abstract

Low-cost, field-deployable, near-time methods for assessing water quality are not available when and where waterborne infection risks are greatest. We describe the development and testing of a novel device for the measurement of tryptophan-like fluorescence (TLF), making use of recent advances in deep-ultraviolet light emitting diodes (UV-LEDs) and sensitive semiconductor photodiodes and photomultipliers. TLF is an emerging indicator of water quality that is associated with members of the coliform group of bacteria and therefore potential fecal contamination. Following the demonstration of close correlation between TLF and E. coli in model waters and proof of principle with sensitivity of 4 CFU/mL for E. coli, we further developed a two-LED flow-through configuration capable of detecting TLF levels corresponding to “high risk” fecal contamination levels (>10 CFU/100 mL). Findings to date suggest that this device represents a scalable solution for remote monitoring of drinking water supplies to identify high-risk drinking water in near-time. Such information can be immediately actionable to reduce risks.

Measuring Environmental Exposure to Enteric Pathogens in Low-Income Settings: Review and Recommendations of an Interdisciplinary Working Group

“…Recent efforts are focused on reducing these product costs and enabling continuous in situ water quality monitoring. 99 …”

“…Escherichia coli ( E. coli ) is the most commonly found fecal coliform bacteria and is more specific to human and animal fecal matter, though genome comparisons suggest that some clades of E. coli primarily originate from nonhost natural environments, and there are reports of E. coli detection in pristine areas of tropical and even temperate environments. − In recent years, several laboratory-grade products have been validated in the field as predictive of E. coli . , However, these instruments require frequent cleaning, are not intended for long-term autonomous operation, are subject to the drawbacks of methods measuring indicators of fecal contamination and are expensive. Recent efforts are focused on reducing these product costs and enabling continuous in situ water quality monitoring …”

“…Recent efforts are focused on reducing these product costs and enabling continuous in situ water quality monitoring. 99 Fecal streptococci were identified as an alternative to total coliform in the 1950s when it became clear that total coliform was a nonspecific indicator for fecal contamination, but the use of this indicator diminished once more specific methods for E. coli culturing were established. 86 Enterococci are a subset of species of the fecal streptococci group, more specific to fecal contamination than fecal streptococci and more persistent in the environment.…”

Optical Properties of Water for Prediction of Wastewater Contamination, Human-Associated Bacteria, and Fecal Indicator Bacteria in Surface Water at Three Watershed Scales

“…The sensor models indicated that currently available T and F fluorescence sensors and turbidity could be used for this purpose. These two sensors have been used in previous efforts for detecting wastewater contamination, ,,− although on a more limited scale or different water matrix than the current study. These models, however, were developed using data from laboratory analysis for T and F. Additional work would be needed to understand the steps necessary to translate these models to a field setting.…”

Advances in quantifying microbial contamination in potable water: Potential of fluorescence‐based sensor technology

“…Tryptophan fluorescence is facilitated by the indole group attached to the molecule and is often referred to as “Tryptophan‐like fluorescence (TLF)” which encompasses both the amino acid identifier and other compounds, such as free indole, that fluoresce at the same wavelength (Aiken, 2014). In environmental fluorescence spectroscopy, the focus is typically on the wavelengths 280 ex /350–60 em nm as this has been shown to be a proxy for biological activity in water (Box 1) (Baker, 2001; Bedell et al, 2020; Bridgeman et al, 2013; Carstea et al, 2010; Cumberland et al, 2012; Sorensen, Baker, et al, 2018).…”