Scientists in Denmark have developed a lipase-based method for the detection of tiny quantities of DNA, which could be used to test for bacteria in beer. 

Rapid and sensitive DNA detection methods have a wide range of uses from cancer and disease diagnosis to the detection of harmful bacteria in food and drink. Previous methods rely on optical methods and a time consuming pre-amplification of the sample, which while sensitive often take several weeks and require bulky apparatus. Electrochemical methods have been used to improve the speed and portability. 

Now, Elena Ferapontova, Kurt Gothelf and colleagues at Aarhus University have developed a lipase-based electrochemical technique that can detect as little as 20 attomoles (2 x 10^-17 moles) of DNA. Lipases are inexpensive ester-cleaving enzymes that find many applications in biotechnology and bioorganic synthesis. 

In Ferapontova's system, the target DNA is captured on a magnetic bead and labelled with the lipase. These are then collected and allowed to react with a ferrocene modified gold electrode. The lipase cleaves the ester bond that holds the electrochemically active ferrocene group onto the electrode, decreasing the signal and indicating the presence of the target DNA. 

Ferapontova says she plans to use the sensor to detect bacterial growth that makes beer go off. 'Any rapid and sensitive method of assaying for spoilage bacteria in beer would be of great economic interest to the brewing industry and would serve the public interest,' she adds. At the moment the team are investigating DNA samples from a known beer spoilage bacteria to test the validity of the method for analysing real beer samples. 

Ben Horrocks, an expert in the biological applications of electrochemistry at Newcastle University, UK, is impressed that the team have married together several existing techniques to produce 'one of the lowest detection limits of an electrochemically-based system'. 

Jon Watson 

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