Colorimetric CO2 indicators were prepared by printing pH dyes (M-cresol purple or phenol red, tetrabutylammonium hydroxide, ethylcellulose, 1:2 ethanol:1-butanol solvent), using a commercially available thermal inkjet printer, on either cellulose paper or plastic transparency film. Indicators inks printed on the papers had higher sensitivity to CO2, greater color change, and more producible than those printed on plastic film. Varying the print intensities of the two pH dyes resulted in multiplexed indicators with tunable sensitivity and expanded detection concentration range towards CO2. The ink-jet printing method is simple and highly flexible for the development of indicator to detect CO2 - a gas indicative of product quality in many food products. Further optimization can potentially lead to application of the indicators in intelligent food packaging systems.
Keywords: Carbon dioxide; Colorimetric indicators; Inkjet-printed; Intelligent packaging; Multiplexing.
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