“Watermark Ink” device identifies unknown liquids instantly

Materials scientists and applied physicists collaborating at Harvard’s School of Engineering and Applied Sciences (SEAS) have invented a new device that can instantly identify an unknown liquid.

The device, which fits in the palm of a hand and requires no power source, exploits the chemical and optical properties of precisely nanostructured materials to distinguish liquids by their surface tension.

The finding, published in the Journal of the American Chemical Society (JACS), offers a cheap, fast, and portable way to perform quality control tests and diagnose liquid contaminants in the field.

“Digital encryption and sensors have become extremely sophisticated these days, but this is a tool that will work anywhere, without extra equipment, and with a very wide range of potential applications,” says co-principal investigator Marko Lončar, associate professor of electrical engineering at SEAS.

Akin to the litmus paper used in chemistry labs around the world to detect the pH of a liquid, the new device changes color when it encounters a liquid with a particular surface tension. A single chip can react differently to a wide range of substances; it is also sensitive enough to distinguish between two very closely related liquids.

Watch a video of the new process.