Scientists working in Spain and the UK have developed a photoelectrochemical sensor that can be used to measure micron-sized objects, and could lead to a faster, more cost-effective tool compared to conventional microscopy.

Richard Compton and his colleagues from Oxford University, UK, and the Centro National de Microelectrónica in Barcelona, Spain, used a net of microelectrodes in a transparent cell to make a self-contained 'photoelectrochemical ruler'. Compton said 'Electrochemistry has long concerned itself with the temporal measurements, such as rates of diffusion and lifetimes of intermediates, but the scope for probing spatial domains in solution has only recently been realised. The question arose as to whether this approach can be used for sizing objects without the need for them to be submerged in solution.' As a test system, Compton used the ruler to measure the thickness of a series of wires.

The wire was placed above the ruler and illuminated from behind, casting a shadow on the array of electrodes. The transparent cell forming the ruler contained a solution that stimulates an electrochemical current only in the presence of light. Compton explained 'The level of the photocurrent decreases with increasing diameter of the wire, as the photochemical reaction is not taking place at the parts of the electrode array that are covered by its shadow.'

By comparing the photocurrent with and without the presence of the wire, its dimensions can be determined readily from the known array spacing. The photoelectrochemical ruler has measured microwires down to 50 µm in diameter.

'Although this seems to be just a basic idea rather than an invention (it could) be of interest from fundamental point of view,' said Ali Eftekhari of Avicenna Institute of Technology, Ohio, US, 'as photoelectrochemical processes can be used for the measurement of physical scales.' Compton concluded 'We are confident that this concept can be expanded to measure smaller objects if the width of the micobands and the separating surfaces are adjusted accordingly.' Isis Innovation, the IP transfer company associated with Oxford University, has applied for a patent on this work and is actively seeking collaborators to commercialise the work.

Michael Spencelayh