Colorimetric Detection of Nickel Ions Using Bacterial Nanocellulose Paper‐Based Strips

ABSTRACT Bacterial nanocellulose (BNC) has proven to be an excellent platform for developing sustainable optical (bio)sensors due to its exceptional properties, including optical transparency, high porosity, and large surface area. These features enable uniform dye distribution, thereby mitigating issues commonly found in paper‐based devices, such as low dye immobilization and non‐uniform color response. Herein, we report a simple, affordable (∼$0.03/strip) BNC‐based colorimetric strip for detecting Ni 2+ ions using digital image analysis. The strips were prepared by functionalizing BNC membranes with the dye 4‐(2‐thiazolylazo)resorcinol (TAR), a complexing agent widely used for the detection of metal ions. Physicochemical characterization confirmed the presence of a porous, interconnected nanofiber network and a hydroxyl‐rich surface, which enabled effective and uniform dye incorporation. The BNC@TAR strips exhibited a linear response up to 10 mg L −1 and a limit of detection of 0.18 mg L −1 . The sensor fabrication process was highly reproducible, and the strips exhibited long‐term stability, maintaining their analytical performance even after 40 days of storage. The strips were also applied to real water analysis, yielding recovery values ranging from 93.1% to 103.4%. These findings support the potential of BNC as a sustainable substrate for developing low‐cost, disposable colorimetric sensors for on‐site environmental monitoring.