Optical Probes for Fe³⁺ Sensing with Cellulose-Based Materials for Bioimaging and Environmental Applications

Iron (Fe³⁺) plays a vital role in numerous biological and environmental systems; however, its abnormal concentration can lead to severe health issues and ecological damage. Conventional analytical methods for Fe³⁺ detection often require sophisticated instrumentation, multi-step sample preparation, and limited portability, restricting their applicability for real-time analysis. In recent years, cellulose-derived colorimetric and fluorimetric sensors have emerged as promising alternatives owing to their biodegradability, abundance, tunable surface chemistry, and strong affinity for metal coordination. This review summarizes the latest advances in the design, fabrication, and sensing mechanisms of cellulose-based materials, including nanocellulose, cellulose composites, and cellulose quantum dots for selective and sensitive Fe³⁺ detection. Moreover, the review highlights their growing applications in environmental monitoring, food safety analysis, and biological imaging, showing their potential for non-toxic, in situ, and real-time sensing.