Microfibrillated cellulose (MFC), a sustainable material derived from biomass, stands out as an environmentally friendly alternative for developing chemical sensors owing to its advantageous properties including high porosity, surface area, and available surface functional groups. Herein, we propose a simple and low-cost strategy for developing cellulose-based strips for the colorimetric detection of total iron in water. The strips were prepared by functionalizing MFC casting membranes with 1-(2-Thiazolylazo)-2-naphthol (TAN), which was characterized by structural and morphological techniques. The sensing ability of the MFC@TAN strips towards total iron was evaluated under distinct reaction times by digital image colorimetry. Under optimal conditions, the strips yielded limits of detections of 0.08 and 0.09 mg L