Portable and Low-Cost Paper-Based Sensor Integrated with Smartphone for Chromium Ions DetectionTeguh Pambudi, Hilman Imadul Umam, Fajar Amelia Rachmawati Putri, Melisa Nur Halimah and Cindy Salsabilla AnjaniE3S Web Conf., 622 (2025) 01011DOI: https://doi.org/10.1051/e3sconf/202562201011