New device can instantly 'fingerprint' unknown liquids

Harvard scientists have created a new pocket-sized device that can instantly identify unknown liquids and may be used by first responders to characterise chemical spills, or by officials to verify the fuel grade right at the pump.
Unlike other techniques for identifying and authenticating liquids, the new technology, called Watermark Ink (W-INK), is inexpensive, instantaneous, and portable.
Developed in the laboratory of Joanna Aizenberg, Professor at the Harvard John A Paulson School of Engineering and Applied Sciences (SEAS), the W-INK concept exploits the chemical and optical properties of precisely nanostructured materials to distinguish liquids by their surface tension.
Akin to the litmus paper used to detect the pH of a liquid, the detector changes colour when it comes in contact with a liquid with a particular surface tension.

The colour-changing strip can be programmed to respond precisely to the unique surface tension exhibited by any liquid of interest.
A new company Validere, cofounded by Harvard University scientists and engineers, will commercialise the W-INK technology.

"Validere translates this technology to create inexpensive, one-time-use test kits that can be used anywhere in the field to visually identify unknown liquids, all without the need for a dedicated power source," said Ian Burgess, CEO at Validere, who co-invented W-INK as a doctoral student at SEAS.
"What our solution does, is to simplify the readouts to a level that you don't need a technician to interpret the results," Burgess said.

"Anyone in the field can immediately know, on the spot, how to respond to a sampled liquid," he said.
W-INK mimics two biological systems to achieve a tunable device with properties that allow it to change colours when it comes in contact with certain liquids.
The wings of some species of butterfly owe their brilliant colours to structure rather than pigment; the surface of each wing contains networks of tiny pores, the size of which determines the perceived colour.
Brittle stars, relatives of starfish can change colour from black to white by modulating the position of pigmented cells inside lens-like, light-focusing structures arranged in an array across the star's back.

By combining both of these mechanisms so that they respond optically to liquid infiltration into chemically modified porous structures, researchers developed a liquid decoder that is small enough to fit in the palm of the hand and can function without a power source.
Engineered surface properties interact with liquids to change the interfacial chemistry of the test strip, which instantly causes corresponding colour changes or markers to appear.
The device will pair with disposable strips to comprise customisable field test kits that can be tailored to identify virtually any liquid or liquid mixture.