Lab Chiphttp://dx.doi.org/10.1039/c2lc40489c (2012)

Colourimetry is a simple and low-cost technique for determining the concentration of coloured compounds in a solution. Although some properties of a compound can result in a colour change in an indicator material, coupling a colourimetric response that is sensitive to a general physical or chemical property is much more of a challenge. Ian Burgess and co-workers from Canada and the USA have now demonstrated a simple colourimetric litmus test for differentiating organic liquids. The test achieves chemical specificity by employing a combination of colourimetric wetting patterns produced from liquids in an array of inverse opal films, each having a graded wettability but using different surface groups to define the wetting gradient. The widespread applicability of this sensing platform is due to its sensitivity to wettability, which is a property of all liquids. A simple-to-use reference-based scoring system allows qualitatively perceptible degrees of wetting to be translated into numerical values, which can then be assigned by eye without the need for sophisticated equipment. This provides chemical specificity without causing a significant sacrifice in terms of portability or ease of use.