Inverse opal technology could help identify chemical spills

The handheld device uses a 3D-nanostructured chip to distinguish liquids by their surface tension, with a colour read-out.

The so-called ‘Watermark Ink’ or ‘W-Ink’ concept relies on a precisely fabricated material called an inverse opal — a layered glass structure with an internal network of ordered, interconnected air pores.

A team at Harvard’s School of Engineering and Applied Sciences (SEAS) discovered that selectively treating parts of the inverse opal with vaporised chemicals and oxygen plasma creates variations in the reactive properties of the pores and channels, letting certain liquids pass through while excluding others.

Allowing liquid into a pore changes the material’s optical properties, so the natural colour of the inverse opal shows up only in the dry regions.

Each chip is calibrated to recognise only certain liquids, but it can be used over and over (provided the liquid evaporates between tests).

One immediate application would allow authorities to verify the fuel grade of petrol right at the pump.

The W-Ink technology would additionally be useful for identifying chemical spills very quickly. A W-Ink chip that was calibrated to recognise a range of toxic substances could be used to determine, on the spot, whether the spill required special treatment.

‘A device like this is not going to rival the selectivity of GC-MS [gas chromatography–mass spectrometry],’ said project co-investigator Prof Joanna Aizenberg of SEAS.

‘But the point is that if you want something in the field that requires no power, is easy to use and gives you an instant result, then the W-Ink may be what you need.’