Recent Developments in Colorimetric and Fluorimetric Sensing of Fe²⁺ and Fe³⁺ Ions: A Review (2021 to 2025)

Iron ions, Fe²⁺ and Fe³⁺, play essential roles in biological, environmental, and industrial processes. However, their imbalance can lead to severe health and ecological issues, including oxidative stress-related diseases and water contamination. Both metal ions are commonly found in environmental water sources, biological fluids, and food products, necessitating their precise detection and quantification. Colorimetric and fluorimetric chemosensors are powerful tools, offering simple, rapid, and highly sensitive methods for monitoring Fe²⁺ and Fe³⁺ ions. These chemosensors are based on changes in color or fluorescence intensity upon interaction with target ions, providing clear and easily interpretable signals. Both types of chemosensors can be designed using organic molecules, polymers, or nanomaterials, each with unique advantages in selectivity, stability, and sensitivity, making them highly effective for environmental and biological ion detection. The aim of this review is to provide a comprehensive overview of the recent advancements in the development of colorimetric and fluorimetric chemosensors for the detection of Fe²⁺ and Fe³⁺ ions, with a focus on innovations from 2021 to 2025. This review explores the progress in organic, polymeric, and nanomaterial-based chemosensors, highlighting their design, sensing mechanisms, and practical applications. By examining the sensitivity, selectivity, and stability of these chemosensors, the review aims to identify key trends, challenges, and future directions in the field, offering valuable insights for researchers and practitioners working on the detection of Fe²⁺ and Fe³⁺ in environmental, biological, and industrial contexts.