Can QR Codes be used to readout Colorimetric Gas Sensors? A Back-Compatible Color QR Code with an Embedded CO2 Sensor Dye

Ismael Benito-Altamirano, Laura Engel, Ferran Crugeira, Miriam Marchena, Cristian Fàbrega, Jürgen Wöllenstein, Joan Daniel Prades

Abstract: Colorimetric dye readout devices have been explored extensively, with many approaches relying on complex hardware setups that stabilize the illuminant and capture conditions, typically involving attachments to smartphones or other digital cameras. In this work, we introduce a cost-effective sensor fabrication pipeline to embed a colorimetric dye in a QR Code, enabling readout by any standard smartphone without the need for specialized equipment. QR Codes, as established machine- readable patterns, offer a robust platform for integrating gasometric active dyes. Our approach ensures the preservation of QR Code data integrity by employing a novel method for maintaining back-compatibility throughout the pattern creation process, avoiding the limitations of dye placement solely in the center or outside the QR Code. We demonstrate this concept by embedding a CO2 sensor dye in a QR Code, while the QR Code presents a link to our website and a traceability ID. The dye is based on a pH-sensitive dye that changes color in the presence of CO2, focused on Modified Atmosphere Packaging (MAP) applications.