ABSTRACT
The methods for cellular imaging should generally be considered in different ways as compared to the design of molecular imaging probes, such as contrast agents. In order to successfully detect cells in vivo or in tissue, sufficient concentrations of imaging moieties need to be incorporated into the cells. For in vivo cellular imaging, the methods can be categorized in two ways; exogenous or endogenous signaling probes for cell labeling, and ex vivo or in vivo cell labeling. In order to perform endogenous cell labeling, gene transfection of a signaling protein into the target cell is necessary. The cell membrane can be labeled either on the cell surface proteins or within the lipid bilayer. Only ions or small molecules, which have specific pumps, are able to pass across the cell membrane, into the cytoplasm of normal cells. Both fluorescence and bioluminescence labeling of cells have been actively investigated ex vivo, especially for microscopic imaging.
