Colorimetric and Fluorimetric Phthalocyanine-Based Sensors for Metal Ion Detection: Recent Advances and Perspectives

Phthalocyanines are highly conjugated macrocyclic compounds that possess remarkable thermal stability, strong absorption in the visible and NIR regions, tunable redox behavior, and versatile structural modifiability. These unique properties, combined with the ability to coordinate various metal ions and incorporate functional substituents, make phthalocyanines excellent platforms for sensing applications. In recent years, important progress has been achieved in the development of phthalocyanine-based colorimetric and fluorimetric sensors for the sensitive detection of metal ions. Phthalocyanine-based sensors offer distinct advantages, including strong optical responses, structural tunability, NIR fluorescence, and compatibility with aqueous and biological systems. Detection mechanisms commonly involve coordination-induced spectral shifts, photoinduced electron transfer (PET), aggregation or disaggregation processes, fluorescence resonance energy transfer (FRET), and heavy metal ion effects, leading to measurable fluorescence or colorimetric changes. This review summarizes recent advances in the design, analytical performance, and practical applications of colorimetric and fluorimetric phthalocyanine-based sensors for metal ions detection. The study highlights sensitivity, selectivity, ratiometric strategies, and real-sample analysis. Current challenges and future perspectives in the development of highly sensitive, selective, and application-oriented phthalocyanine sensors are also discussed, highlighting their potential in biomedical analysis, environmental monitoring, and industrial applications.