Dual emissive carbon dots as Ratiometric fluorescence sensors: A comprehensive review

Ratiometric fluorescence sensing offers significant advantages over traditional fluorescence techniques due to its inherent self-referencing nature, enabling robust and accurate measurements. This review focuses on the utilization of Carbon Dots (CDs) as promising platforms for developing ratiometric fluorescence sensors RFS. It outlines the fundamental principles of ratiometric sensing, highlighting its advantages over traditional fluorescence methods. The sensing mechanisms employed in ratiometric sensors are discussed, including intramolecular charge transfer (ICT), fluorescence resonance energy transfer (FRET), chelation-enhanced fluorescence (CHEF), photoinduced electron transfer (PET), excited-state intramolecular proton transfer (ESIPT), aggregation-induced emission (AIE), static quenching effect (SQE), dynamic quenching (DQE) and internal filtration effect (IFE). Furthermore, various methods for constructing CD-based RFS are investigated in this review, including surface functionalization, doping, mixing strategy, hybridization/compositing, and synthesis of intrinsic dual-emissive CDs. In addition, the diverse applications of CD-based RFS in key areas are discussed, such as environmental monitoring, food safety analysis, pharmaceutical analysis, bioanalysis, and bioimaging. Finally, this review highlights the challenges associated with CD-based RFS and outlines potential directions for future research.