Color QR Codes for Smartphone-Based Analysis of Free Chlorine in Drinking Water
Free chlorine (FC) plays a crucial role in ensuring the safety of drinking water by effectively inactivating pathogenic microorganisms. However, traditional methods for measuring FC levels often require specialized equipment and laboratory settings, limiting their accessibility and practicality for...
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MDPI AG
2025-05-01
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| Series: | Sensors |
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| Online Access: | https://www.mdpi.com/1424-8220/25/11/3251 |
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| author | María González-Gómez Ismael Benito-Altamirano Hanna Lizarzaburu-Aguilar David Martínez-Carpena Joan Daniel Prades Cristian Fàbrega |
| author_facet | María González-Gómez Ismael Benito-Altamirano Hanna Lizarzaburu-Aguilar David Martínez-Carpena Joan Daniel Prades Cristian Fàbrega |
| author_sort | María González-Gómez |
| collection | DOAJ |
| description | Free chlorine (FC) plays a crucial role in ensuring the safety of drinking water by effectively inactivating pathogenic microorganisms. However, traditional methods for measuring FC levels often require specialized equipment and laboratory settings, limiting their accessibility and practicality for on-site or point-of-use monitoring. QR Codes are powerful machine-readable patterns that are used worldwide to encode information (i.e., URLs or IDs), but their computer vision features allow QR Codes to act as carriers of other features for several applications. Often, this capability is used for aesthetics, e.g., embedding a logo in the QR Code. In this work, we propose using our technique to build back-compatible Color QR Codes, which can embed dozens of colorimetric references, to assist in the color correction to readout sensors. Specifically, we target two well-known products in the HORECA (hotel/restaurant/café) sector that qualitatively measure chlorine levels in samples of water. The two targeted methods were a BTB strip and a DPD powder. First, the BTB strip was a pH-based indicator distributed by Sensafe<sup>®</sup>, which uses the well-known bromothymol blue as a base-reactive indicator; second, the DPD powder was a colorimetric test distributed by Hach<sup>®</sup>, which employs diethyl-p-phenylenediamine (DPD) to produce a pink coloration in the presence of free chlorine. Custom Color QR Codes were created for both color palettes and exposed to several illumination conditions, captured with three different mobile devices and tested over different water samples. Results indicate that both methods could be correctly digitized in real-world conditions with our technology, rendering a 88.10% accuracy for the BTB strip measurement, and 84.62% for the DPD powder one. |
| format | Article |
| id | doaj-art-8a5f7b8030064a31830b60a23cf49c36 |
| institution | DOAJ |
| issn | 1424-8220 |
| language | English |
| publishDate | 2025-05-01 |
| publisher | MDPI AG |
| record_format | Article |
| series | Sensors |
| spelling | doaj-art-8a5f7b8030064a31830b60a23cf49c362025-08-20T03:11:32ZengMDPI AGSensors1424-82202025-05-012511325110.3390/s25113251Color QR Codes for Smartphone-Based Analysis of Free Chlorine in Drinking WaterMaría González-Gómez0Ismael Benito-Altamirano1Hanna Lizarzaburu-Aguilar2David Martínez-Carpena3Joan Daniel Prades4Cristian Fàbrega5Department of Electronic and Biomedical Engineering, Universitat de Barcelona, Martí i Franquès 1, 08028 Barcelona, SpainDepartment of Electronic and Biomedical Engineering, Universitat de Barcelona, Martí i Franquès 1, 08028 Barcelona, SpainDepartment of Electronic and Biomedical Engineering, Universitat de Barcelona, Martí i Franquès 1, 08028 Barcelona, SpainDepartment of Electronic and Biomedical Engineering, Universitat de Barcelona, Martí i Franquès 1, 08028 Barcelona, SpainDepartment of Electronic and Biomedical Engineering, Universitat de Barcelona, Martí i Franquès 1, 08028 Barcelona, SpainDepartment of Electronic and Biomedical Engineering, Universitat de Barcelona, Martí i Franquès 1, 08028 Barcelona, SpainFree chlorine (FC) plays a crucial role in ensuring the safety of drinking water by effectively inactivating pathogenic microorganisms. However, traditional methods for measuring FC levels often require specialized equipment and laboratory settings, limiting their accessibility and practicality for on-site or point-of-use monitoring. QR Codes are powerful machine-readable patterns that are used worldwide to encode information (i.e., URLs or IDs), but their computer vision features allow QR Codes to act as carriers of other features for several applications. Often, this capability is used for aesthetics, e.g., embedding a logo in the QR Code. In this work, we propose using our technique to build back-compatible Color QR Codes, which can embed dozens of colorimetric references, to assist in the color correction to readout sensors. Specifically, we target two well-known products in the HORECA (hotel/restaurant/café) sector that qualitatively measure chlorine levels in samples of water. The two targeted methods were a BTB strip and a DPD powder. First, the BTB strip was a pH-based indicator distributed by Sensafe<sup>®</sup>, which uses the well-known bromothymol blue as a base-reactive indicator; second, the DPD powder was a colorimetric test distributed by Hach<sup>®</sup>, which employs diethyl-p-phenylenediamine (DPD) to produce a pink coloration in the presence of free chlorine. Custom Color QR Codes were created for both color palettes and exposed to several illumination conditions, captured with three different mobile devices and tested over different water samples. Results indicate that both methods could be correctly digitized in real-world conditions with our technology, rendering a 88.10% accuracy for the BTB strip measurement, and 84.62% for the DPD powder one.https://www.mdpi.com/1424-8220/25/11/3251free chlorineQR Codecolorimetric analysiscomputer visionmachine learningwater quality |
| spellingShingle | María González-Gómez Ismael Benito-Altamirano Hanna Lizarzaburu-Aguilar David Martínez-Carpena Joan Daniel Prades Cristian Fàbrega Color QR Codes for Smartphone-Based Analysis of Free Chlorine in Drinking Water Sensors free chlorine QR Code colorimetric analysis computer vision machine learning water quality |
| title | Color QR Codes for Smartphone-Based Analysis of Free Chlorine in Drinking Water |
| title_full | Color QR Codes for Smartphone-Based Analysis of Free Chlorine in Drinking Water |
| title_fullStr | Color QR Codes for Smartphone-Based Analysis of Free Chlorine in Drinking Water |
| title_full_unstemmed | Color QR Codes for Smartphone-Based Analysis of Free Chlorine in Drinking Water |
| title_short | Color QR Codes for Smartphone-Based Analysis of Free Chlorine in Drinking Water |
| title_sort | color qr codes for smartphone based analysis of free chlorine in drinking water |
| topic | free chlorine QR Code colorimetric analysis computer vision machine learning water quality |
| url | https://www.mdpi.com/1424-8220/25/11/3251 |
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