Down to the wire

The laws of physics are strange at nano-scale. Take optical fibres, for example. Normal-size fibres act like pipes, with the light flowing inside the confines of the strands of glass. But make the fibre smaller — below the wavelength of the light — and the light will leak out of the sides of the strand while still following its path.

Using this odd property, researchers from

are building a sensor sensitive enough to analyse solutions so weak that they contain only one molecule of target compound in 10 million of solvent. Ten times more sensitive than anything else available, the sensors are likely to find applications in forensics and security-related sectors.

The sensitivity of the technique could allow the detection of small amounts of explosives or toxins and will also allow forensics experts to test extremely small samples gathered from crime scenes.

Gilberto Brambilla's team at the university's optoelectronics research centre makes the nanowires from standard optical fibres and stretches them carefully to reduce the diameter almost a thousand-fold. The sensor will use fibres around 400nm in diameter, although Brambilla said his stretching technique can produce diameters as low as 50nm.