Environmental Engineering Reference
In-Depth Information
children die every day worldwide from fecally contaminated drinking water alone.
World Health Organization and United Nation's Children Fund estimate 1.8 million
deaths from water related diseases out of which 1.6 million are children of ages 5 or
under. Such risks are not completely eliminated even with the best practices in the water
treatment industry. In part this is due to many emerging and reemerging infectious
diseases. At least 35 new agents of disease have been added to this list between 1972
and 1999.
Traditionally, the predominant techniques used to identify the waterborne
pathogens rely upon culture-based approaches, which is selective and time consuming.
Polymerase chain reaction based assays (real time or end point) are becoming common,
but they are yet to be widely adopted by the drinking water treatment industry. The
extent of adoption is mainly governed by the lack of regulation to directly measure the
pathogens. Specificity, sensitivity, quantitation, speed, ruggedness and the ability to
handle large volumes of water are among the key characteristics needed for any assay
used for waterborne pathogen detection. Specificity is critical due to the presence of
numerous microbial species present in the background. Sensitivity and quantitation are
important because very low doses (e.g., it is 10 to 100 cells for Escherichia coli
O157:H7) can be a serious health risk (Nataro and Kaper, 1998). As a consequence there
are more than 100 kits available in the market to detect E. coli with varying ability to
resolve at the strain level. Nanosensors are not far behind in this race. The very first
product that was launched by a company with the same name (i.e., NanoSensors Inc.)
focused on a disposable biosensor kit for E. coli . Ruggedness is a required trait because
highly trained microbiologist and molecular biologists are not available at all treatment
plants. Speed of an assay is important because of the need to ensure the safety of water
before it reaches the consumer.
Micro and nano-scale sensors have the potential to meet most of the above
requirements leading to highly sensitive, specific, and rapid platform for detection of
waterborne pathogens. Many studies have been reported targeting various biological
molecules and transduction techniques for a number of pathogens (Table 13.1).
However, at present there are very few assays that meet the requirements in terms of
assay time and detection limit. As indicated earlier, the ability to process large volumes
of water and sample preparation are critical steps in the application of biosensor
technology to water environment. Sample preparation includes the concentration of large
quantities of water (1 to 100 L) to a few μL that could be applied to the biosensor
platform. A number of factors associated with sample processing like reliability, batch
processing of samples, presence of inhibitory substances etc. are the major challenges
for the use of biosensor for water industry (Lim et al., 2005).
This chapter summarizes the characteristics, working mechanism and type of
commonly used micro- and nano-scale sensors. Fabrication/synthesis techniques and
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