Scientists in the US have made a low-cost, disposable paper device to test the purity of drinking water. 

George Whitesides, Zihong Nie and colleagues at Harvard University, Cambridge, US have designed a paper-based electrochemical device that can detect tiny concentrations of heavy metal ions in water. 

Heavy-metal ions such as mercury, lead, and cadmium are toxic, non-biodegradable, and can find their way into humans and animals via drinking water. Whitesides' device can detect lead in water at levels as low as one part per billon (ppb), which is much lower than the World Health Organization guideline value (<10 ppb) for the safe level of lead in drinking water. What's more, it only costs 2 cents to make and no qualified personnel or complicated instruments are needed to use them. 

Low-cost, paper-based analytical devices are attractive for use in developing countries. 'Our paper-based diagnostic devices can provide average families and families with limited resources a way to test the safety of their drinking water,' explains Nie. 

Three carbon and silver ink electrodes are printed onto a piece of paper or polyester film to make the device. Microfluidic channels created from polymers are patterned on the paper and form hydrophobic barriers to confine liquids in the channels and over the electrodes. 

The team say that the devices are versatile and could have many other uses. For instance in medical diagnosis of diseases such as HIV, tuberculosis and malaria or environmental monitoring developing areas. 'It can also be applied to food inspection for the common household,' adds Nie. 

'This is nice work using paper-based microfluidics. The incorporation of electrochemical sensing opens up a broad range of possibilities extending the number of assays that can be performed,' comments David Holmes, an expert in microfluidics biosensors and biomedical devices at University College London, UK. 

Michael Brown 

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