“W-Ink Technology”- Powerless Device To Detect Unknown Liquid Formulations

Harvard's  School of Engineering and Applied Sciences (SEAS) have come up with a chip that can detect unknown liquids within seconds. The technology used to develop the chip is called as Wireless Ink or simply W-Ink. The device can detect the liquid by changing its own color or even by displaying pre-programmed message when the liquid to be tested is applied on its surface. Even though the chip looks extremely normal at first sight, it is a result of amalgamation of myriad technologies such as optics, chemistry, condensed matter, fluidics and nanotechnology.

The chip is made up of complexly structured nano crystals in 3 dimensions. The structure is in the form of many layers. Each individual layer is made up of glass in nano dimensions. The glass forms a network that is interconnected in such a way that air pores are created. These structured are termed as inverse opal by the scientists. The chip detects the liquid based on the surface tension it encounters when it is wetted by the liquid. Each liquid has a surface tension that is unique to itself. Hence, every liquid will make the chip to change its color, different in each case, depending on the surface tension.

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Chip changes its color for different liquid. (Credit:Ian Burgess)

This device developed by Ian B. Burgess and team was possible due to the developments made in production of the inverse opals by Lidiya Mishchenko (a graduate student at SEAS) and Benjamin D. Hatton (a research appointee at SEAS and a technology development fellow at the WYSS Institute for Biologically Inspired Engineering at Harvard). The initial difficulty faced by researchers was the realization of selective wetting of the chip with a greater precision. The 3D structure was essential for using the optical and fluidic properties at its fullest.

The detection of the liquid depends on two factors: the surface chemistry of the liquid and the degree to which the liquid affects the pore structure. The color of the opal structure depends on how much has the liquid has passed through the porous opal structure. When a dry chip is held in air, it shows its natural color. No liquid has entered the pores and we can see the chip as mere green in color. However, as soon as the chip is dipped in liquid or just sprayed with the liquid, the chip changes its color. The change in color can be attributed to the change in optical properties of the liquid when it has entered the pores of the opal structure.

The scientists were successfully able to control which liquid passed through the pores or not. They achieved this by treatment of some parts of opal structure by vaporized chemicals and oxygen plasma in a selective manner. This resulted in the change in reactive properties of the chip and detection of a specific solvent efficiently. The opal chip is in its normal mode when it is dry. As soon as it becomes wet due to any kind of solvent, it changes its optical properties and hence its color changes.

The advantage of using this chip is that a single chip can be used to detect different kinds of liquids. As it does not need any power to function, it can be used a large number of times without any worries regarding the power consumption. It can also categorically differentiate two liquids having very similar surface tensions. However, the most exciting part is that is you do not need a separate chart just to verify the color on the chart and chip to know which liquid has been detected. The chip can be designed to display separate messages when it detects different liquids. Therefore, you know whether you have detected ethanol or water just by looking at the chip! The video tells it all.


The chip does not promise to offer extremely high degree of selectivity like gas chromatography–mass spectrometry techniques but it can provide beneficial for applications where such high degree of efficiency is not required. Immediate applications can be use of the chip to detect any adulteration in various industrial liquids, gasoline, etc. The content of methanol in liquor will be easy, fast and will not require any power! A paper on this innovative technology has been already published in Journal of the American Chemical Society. Funded by Air Force Office of Scientific Research, Natural Sciences and Engineering Research Council of Canada and U.S. Department of Homeland Security (DHS) and other institutions, the technology is been tested in different government agencies. We can hope for a commercially viable product that we can use in our homes and at gasoline stations to detect any adulteration and the exact composition of any liquid. Then and there.

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