The supply of safe potable water, free from pathogens and chemicals, requires routine analyses and the application of several diagnostic techniques. Apart from being expensive, many of the detection methods require trained personnel and are often time-consuming. With drastic climate changes, severe droughts, increases in population and pollution of natural water systems, the need to develop ultrasensitive, low-cost and hand-held, point-of-use detection kits to monitor water quality is critical. Although Escherichia coli is still considered the best indicator of water quality, cell numbers may be below detection limits, or the cells may be non-culturable and thus only detected by DNA amplification. A number of different biosensors have been developed to detect viable, dead or non-culturable microbial cells and chemicals in water. This review discusses the differences in these biosensors and evaluates the application of microfluidics in the design of ultra-sensitive nano-biosensors.

Polyclonal antibodies against Escherichia coli and fluorescent, secondary, antibodies were immobilized on borosilicate glass fibers pre-treated with 3-glycidyloxypropyl trimethoxysilane (GPS). Light with an average wavelength of 627 nm, emitted by a diode placed at one end of the glass fiber, was detected by an ultrasensitive photodiode with peak sensitivity at 640 nm. Changes in fluorescence, caused by binding of E. coli to the antibodies, changed the net refractive index of the glass fiber and thus the internal reflection of light. These evanescent changes in photon energy were recorded by an ultrasensitive photodiode. Signals were amplified and changes in voltage recorded with a digital multimeter. A linear increase in voltage readings was recorded over 2 h when 3.0 × 10 CFU/ml and 2.77 × 10 CFU/ml E. coli were adhered to the antibodies. Voltage readings were recorded with E. coli cell numbers from 2 × 10 CFU/ml to 2 × 10 CFU/ml, but readings remained unchanged for 2 h, indicating that the limit of detection is 3.0 × 10 CFU/ml. This simple technology may be used to develop a low-cost, portable, fiber-optic biosensor to detect E. coli in infections and may have applications in the medical field. Research is in progress to optimize the sensitivity of the fiber-optic biosensor and determine its specificity.

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The Papillion Creek Watershed in Nebraska and the Arkansas River system in Kansas share many similar qualities. Both systems include cities that are roughly equivalent in size-Omaha, Nebraska and Wichita, Kansas. Both have a similar mix of urban and agricultural land use, and both share a similar topography. Both fecal coliform bacteria (FCB) studies used statistical modeling, trend line analyses, mass loading analyses and fate-transport dynamic modeling. Specific examples and findings are compared and discussed.While both studies shared similarities, the Wichita water quality study is unique in that, in addition to water column grab sample data, it includes sediment sampling data, Antibiotic Resistance Analyses (ARA), and dry weather and wet weather hydrographic sampling at fourhour intervals; the latter of which provided actual fate-transport patterns.Technical findings from the Wichita data add valuable insights about the potential longevity of fecal coliform bacteria. It has been widely believed that outside of the host organism, FCB will typically survive for 24 to 48 hours. Testing results from the Wichita study showed that FCB persist for extended periods of time in sediment, including relatively cold-water conditions. Hydrographic sampling during dry weather, non-runoff conditions uncovered a distinct diurnal pattern that was highly suggestive of sediment as being a significant source of FCB.Technical findings to date from water quality modeling for FCB for both studies suggest:• FCB levels are highly dependent on runoff events and sediment transport mechanisms.• FCB levels are well above surface water quality standards for "summer season" primary contact recreation. • Urbanized areas contribute approximately another order of magnitude above already high non-urban contributions of FCB under median weather conditions. • It is possible that background FCB levels from wildlife alone may be higher than standards currently allow.• Comprehensive best management practices will be required to control sediment, bacteria, and nutrients. • Regulatory compliance for FCB will be difficult. KEYWORDSFecal coliform bacteria, water quality modeling, WASP, MIKE11, watershed impairment.