Immunofluorescence is only limited to fixed ( i.e. , dead ) cells when structures within the cell are to be visualized .
Antibodies do not penetrate the cell membrane when reacting with fluorescent labels .
Immunofluorescence is only limited to fixed ( i.e. , dead ) cells when structures within the cell are to be visualized because antibodies do not penetrate the cell membrane when reacting with fluorescent labels .