Sanmartín Matalobos, JesúsBermejo Barrera, PilarGarcía Deibe, Ana MaríaFondo Busto, María MatildeAlves Iglesias, Yeneva2025-10-142025-10-142025Sanmartín-Matalobos, J., Bermejo-Barrera, P., García-Deibe, A.M. et al. Convenient colorimetric approach to quantify CuO NPs in water using only a smartphone and cellulose paper with an immobilised chemosensor. Microchim Acta 192, 594 (2025). https://doi.org/10.1007/s00604-025-07439-9https://hdl.handle.net/10347/43072A novel approach is reported to quantify CuO NPs in aqueous samples by using digital image colorimetry (DIC), which is a rapid, low-cost, and facile method. We have used a colour recogniser application on a smartphone to register the gradual colour changes experimented, under λex = 365 nm radiation, by a dansyl-based chemosensor immobilised on cellulose paper, after interacting with aqueous dispersions of CuO NPs with concentrations between 5 and 100 µg L−1. The low limits of detection (LOD) and quantification (LOQ) (10.5 and 34.9 µg L−1, respectively) show a relevant sensitivity for this simple method, which also displays a good precision and accuracy (analytical recovery, 99 ± 1%). A comparison of the results similarly obtained for the modified paper through diffuse reflectance (DR) revealed worse detection parameters (LOD = 100.0 µg L−1 and LOQ = 333.4 µg L−1). In addition, fluorescence spectroscopy (λem = 520 nm) demonstrated the ability of the free chemosensor (1.26 µg L−1 in 20:80 (v/v) water–ethanol solutions) for the quantification of CuO NPs (LOD = 30 µg L−1 and LOQ = 101 µg L−1), without improvement of the results obtained with DIC on the modified papers. The dissolved free chemosensor demonstrated selectivity towards CuO NPs in the presence both of metal ions common in aqueous samples as K+, Na+, Ca2+, Mg2+, Fe3+, or Al3+ and of other usual nanomaterials as those of Cu, CdSe, TiO2, and ZnO NPseng© The Author(s) 2025. This article is licensed under a Creative Commons Attribution 4.0 International License, which permits use, sharing, adaptation, distribution and reproduction in any medium or format, as long as you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons licence, and indicate if changes were made. The images or other third party material in this article are included in the article's Creative Commons licence, unless indicated otherwise in a credit line to the material. If material is not included in the article's Creative Commons licence and your intended use is not permitted by statutory regulation or exceeds the permitted use, you will need to obtain permission directly from the copyright holder. To view a copy of this licence, visit http://creativecommons.org/licenses/by/4.0/Attribution 4.0 Internationalhttp://creativecommons.org/licenses/by/4.0/CuO NPsChemosensorFluorescenceDiffuse reflectanceSmartphone assisted detectionjournal article10.1007/s00604-025-07439-9open access