Microbial water quality: Voltammetric detection of coliforms based on riboflavin–ferrocyanide redox couples

It is well established that drinking water contaminated with faecal matter poses a series risk of waterborne disease yet, it is estimated that almost 2 million people are reliant on such sources. The production of improved water sources for low- and middle-income countries has been a long-standing international commitment but ensuring that the drinking water is safe to drink remains a challenge – particularly in rural communities. The development of low-cost diagnostic systems capable of detecting coliform contamination is clearly required. The design of a disposable microfluidic based device that integrates the preconcentration, culture and detection of E. coli is presented as a possible solution. The device is based on a thin layer conductive carbon fibre filter modified with a riboflavin – ferrocyanide redox couple. The device utilises the fermentation characteristics of captured indicator bacteria to lower the local pH by the production of lactic acid and pyruvate after the introduction of lactose. The process can be monitored voltammetrically whereby ferrocyanide (internal reference) and riboflavin (pH probe) are readily detectable at the carbon fibre filter and allows the indirect measure of the change in pH as a function of time and bacterial concentration. The construction of the device and the electroanalytical responses are presented and the analytical efficacy, in terms of bacterial detection and in relation to present WHO criteria, is critically evaluated.