Abstract
Easy-to-use sensors for ethanol solutions have broad applications ranging from monitoring alcohol quality to combating underage drinking. Although there are a number of electronic and colorimetric sensors available for determining alcohol concentration, there is currently no device that can concurrently provide a prompt, well-defined, quickly recoverable readout and remain readily affordable. Here, we developed a field-ready, colorimetric indicator that provides a fast, clear identification of ethanol-water mixtures between 0 and 40% based on the discoloration of a wetted photonic crystal. We cooperatively exploit the iridescence and the geometrical gating in silica inverse opal films (IOFs), together with a fine-tuned surface chemistry gradient, to distinguish ethanol concentrations by their wettability patterns in the different segments of the IOFs. The resultant all-in-one colorimetric sensor delivers a striking and instantaneous optical response at an ethanol concentration as low as 5%. We further improve the ease of use by seamlessly integrating this colorimetric platform with drinking glassware (a glass stirrer and a vial). This research provides an optimal means for colorimetric ethanol detection and is a step toward the immersible sensing of diverse molecules (e.g., biomarkers) in aqueous solutions without expensive laboratory tests.
Highlights
Measuring ethanol content in a fast and straightforward manner has profound implications for quality control and legitimate consumption of alcoholic beverages
To make an inverse opal, a direct opal is used as a sacrificial template that is first infiltrated with a matrix material and removed
We fabricated thin film inverse opals using evaporation-induced co-assembly of a polystyrene colloidal template and silica matrix material formed from the polycondensation of tetraethyl orthosilicate (TEOS).[38]
Summary
Measuring ethanol content in a fast and straightforward manner has profound implications for quality control and legitimate consumption of alcoholic beverages. We developed a field-ready, colorimetric indicator that provides fast, clear identification of ethanol/water mixtures between 0 to 40% based on the discoloration of a wetted photonic crystal. W-Ink uses interconnected highly ordered inverse opal films (IOFs) and silane surface functionalization to control the infiltration of liquid into the structure.
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