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ABSTRACT
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.
Keywords: Biosensors, microfluidics, nano-biosensors, E. coli detection
INTRODUCTION
The increase in population numbers, industrial pollution and changes in climate are the main factors leading to water scarcity and a decrease in the quality of potable water (Water Supply and Sanitation Technology Platform, 2006). Polluted water accounts for millions of deaths per annum, especially amongst children under the age of five (WHO, 2003; WHO and UNICEF, 2006). Most of these communities live in droughtstricken countries, often in rural and less developed areas (WHO and UNICEF, 2006). Ten years ago, the World Health Organisation (WHO) and UNICEF estimated that 1.7 billion people in rural areas will not have access to clean, potable water and sanitation (WHO and UNICEF, 2006). The current situation is alarming. Communities in undeveloped rural areas usually have no water purification plants and are prone to develop life-threatening diseases. In many cases, they have to rely on rivers, open reservoirs, springs and open wells for drinking water (WHO and UNICEF, 2006; WHO and United Nations Children's Fund, 2000; Ministry of Health and Social Welfare and WHO, 2002; Gwimbi, 2011). The lack of proper sanitation facilities exacerbates the problem and wells with drinking water are often located close to dug-out latrines, bathing areas and animal camps (WHO and UNICEF, 2006; Ministry of Health and Social Welfare and WHO, 2002; Gwimbi, 2011). Due to the lack in finances and infrastructure, water supplies in...