Carbocyanine dyes, including DiO (DiOC18(3)), DiI (DiIC18(3)), DiD (DiIC18(5)), DiR, and the dialkyl aminostyryl dye DiA (4-Di-16-ASP), are employed for marking membranes and other hydrophobic structures. These dyes possess high extinction coefficients, display environmental-dependent fluorescence, and exhibit short excited-state lifetimes in lipid environments, becoming fluorescent and photostable when integrated into membranes or attached to lipophilic biomolecules^[1].

DiO, DiI, DiD, and DiR provide green, orange, red, and infrared fluorescence, respectively, enabling multicolor imaging and flow cytometric analysis of live cells. DiO and DiI are compatible with standard FITC and TRITC filters, respectively. DiI and its analogs, known for their minimal cell toxicity, are frequently used for labeling lipoproteins such as LDL and HDL. DiA is commonly utilized in neuronal tracing^[2].