Combinatorial Wetting in Colour: An Optofluidic Nose

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Original Entry by Cheng Wang, AP225, Fall 2012


General Information

Authors: Kevin P. Raymond, Ian B. Burgess, Mackenzie H. Kinney, Marko Loncar and Joanna Aizenberg

Publication: Raymond et al., "Combinatorial wetting in colour: an optofluidic nose" (2012) 12: 3666-3669

Keywords: Wetting, colourimetric, chemical test, array


Summary

Colourimetry is powerful in chemical sensing and its biggest challenge is to couple colourimetric response sensitive to general physical or chemical property. This work is based on a previous platform for colourimetry called Wetting In Colour Kit (WICK)Encoding complex wettability patterns in chemically functionalized 3D photonic crystals. In WICK, the macroscopic colour depends on the number of unfilled (unwetted) layers. As the total number of layers changes across the sample, the structural colour pattern is highly sensitive to the liquid's wettability. However, this WICK method is only sensitive to the surface property. It cannot give any chemical information without prior-given information. From Fig 1B we can see that n-octane gives the same result as 80% EtOH, while Acetone is able to mimick the colourimetric response of 90% EtOH.

In this paper, the authors use an array of WICKs with slightly different chemical responses. The combinatorial patterns in the array gives more chemical information about the liquid, as Fig. 1C shows. The system consists of 6 different WICKs. Different concentrated EtOH and IPA are used as reference liquids, and the test liquid is scored by comparing its array pattern with reference pattern. This paper demonstrated the ability to differentiate 17 organic solvents.

This novel "optofluidic nose" is not so highly selective compared to other previously reported "artificial nose". Its biggest advantage, however, lies in that it is easy to use, by simply comparing the colourimetric pattern with naked eyes, just like what we do in pH test paper.