Ammonium alginate and cellulose nanofiber-based sea anemone tentacle-inspired colorimetric gas-sensitive aerogel enabling ultra-sensitive ammonia visual detection

Real-time visual detection of ammonia (NH₃) is crucial for environmental safety and food quality, yet traditional sensors often suffer from slow response, poor selectivity, and limited adaptability. Here, we innovatively report an ammonium alginate (AL) and cellulose nanofiber-based colorimetric aerogel (APPC aerogel) with a sea anemone-inspired structure for rapid, sensitive, and reversible NH₃ detection. The aerogel is prepared by embedding a sulfonated indole photoacid (PMUH) into a matrix of AL, cellulose nanofibers (CNF), and phytic acid (PA), cast into a 3D-printed template, and directionally frozen to form an ordered porous bionic structure. Upon NH₃ exposure, PMU-H undergoes fast, reversible proton transfer and enol-keto tautomerization, producing a color change from yellow to purplish-red within 5 s. The aerogel shows a detection limit of 0.65 ppm, a linear range of 1–250 ppm, and maintains performance over 50 cycles. FTIR and DFT analyses reveal the sensing mechanism. The material remains stable under humidity, temperature variations, and complex gases, enabling effective visual monitoring of NH₃ during seafood spoilage and offering promise for food packaging, environmental monitoring, and safety applications.