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

The ability to screen water for the presence of faecal contamination is a pressing need for rural communities dependent upon local purification systems. While there are a multitude of coliform detection assays based on the activity of β-galactosidase, this report details the adaptation of a voltammetric pH sensing strategy which could offer rapid analysis. The approach exploits the bacterial metabolism of lactose via pyruvate to lactate with the subsequent decrease in pH measured by examining the peak separation of a riboflavin (sensing)-ferrocyanide (reference) couple. Disposable carbon fibre electrodes were used as in situ sensors in Escherichia coli cultures (103–107 cfu/mL) with detection times of 4h enabling confirmation of coliform activity. The bacterial compatibility of the riboflavin–ferrocyanide system in combination with the simplicity of the detection methodology, stand in marked contrast to many existing coliform assays and could open new avenues through which voltammetric pH sensing could be employed.