Labeling membranes with carbocyanine dyes (DiIs) as phospholipid analogs

Cell membranes can be labeled with cationic lipophilic fluorescent carbocyanine dyes that function as phospholipid analogs. These dyes, such as DiI-C(16)(3) (1,1'-dihexadecyl-3,3,3',3'-tetramethylindocarbocyanine perchlorate), label the plasma membrane and (eventually) label all of the membranes within a living cell. The dyes can be also used with model membranes. Carbocyanine dyes are commercially available in different carbon chain lengths (e.g., C(12), C(14), C(18), and C(22)). Depending on the fatty acid composition of the phospholipids in the membrane studied with respect to chain length and degree of saturation, DiIs with different chain lengths can provide optimal incorporation and accurate reporting of membrane motions. DiI-labeled cells can be studied using fluorescence microscopy or fluorescence recovery after photobleaching (FRAP), as well as other techniques.