A hot copper wire can detect important biochemical intermediates, say Chinese scientists.

Jian-Jun Sun and colleagues at Fuzhou University used thin copper wire to make an oxide-covered copper electrode, which they heated using an electric current. They found that the high temperature accelerated redox reaction rates at the electrode, enabling sensitive detection of polyhydroxylated compounds, such as shikimic acid (SA).

SA is a biochemical intermediate found in plants and microorganisms. It is also an effective anti-thrombosis drug and is used to make Tamiflu, the antiviral drug currently being used to treat swine flu. SA cannot be synthesised cheaply and so most of it is extracted from star anise. As the demand for Tamiflu increases and scientists look for new ways to produce SA, its determination and extraction are of great interest, says Sun.

Until now, scientists have detected SA using a UV detector coupled to liquid chromatography or capillary electrophoresis separation techniques. No electrochemical methods for detection have been reported before, comments Sun, because SA's functional groups cannot be easily oxidised or reduced using traditional bare electrodes made from glassy carbon, gold or platinum.

The heated oxide-covered electrode (HOCE) electrochemically detects SA by electrocatalytically oxidising its hydroxy groups. It can detect SA levels as low as 0.01 parts per million, much lower than the UV detection limit of 0.3 parts per million, Sun explains. He adds that it also shows good responses for other analytes, including glucose, amino acids, purine bases and ribonucleosides.

'The idea of using thin metal wires and passing a current through them to heat them in solution is both simple and elegant,' remarks Phil Bartlett, an expert in electrochemistry at the University of Southampton, UK. 'Extending this to metals such as copper, where a catalytic oxide can be formed, has great promise, since it does not require significant capital investment or complex equipment to apply.'

Many analytes exhibit similar electrocatalytic responses to shikimic acid, meaning that their voltammetric peaks overlap. To overcome this problem, the electrochemical detector must be coupled with separation techniques such as high performance liquid chromatography or capillary electrophoresis, says Sun. 'The design of a heated electrode adapted to the interface of the [separation] instrument is the primary challenge,' he adds.

Philippa Ross

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