Photobleaching Comparison of R-Phycoerythrin-Streptavidin and Streptavidin-Alexa Fluor 568 in a Breast Cancer Cell Line

Fluorescent dyes are excited by light and emit light at a longer wavelength. Photobleaching is one the most important obstacles in fluorescent image capturing. Photochemical alteration of a fluorescent dye caused by several excitation/emission cycles results in a fluorophore to be unable to emit light. In this study, R-phycoerythrin (R-PE) and Alexa Fluor 568 were separately conjugated to streptavidin. The efficiency of conjugations, R-PE-streptavidin and streptavidin-Alexa Fluor 568, were evaluated by sodium dodecyl sulfate polyacrylamide gel electrophoresis and spectrophotometry, respectively. Herceptin, a humanized therapeutic antibody, was subsequently biotinylated. The reactivity of biotin-labeled Herceptin was examined by enzyme-linked immunosorbent assay. The photobleaching of R-PE-streptavidin and streptavidin-Alexa Fluor 568 were then compared in an immunofluorescent staining on a breast cancer cell line, BT-474. Our data showed that streptavidin-Alexa Fluor 568 was more photostable than R-PE-streptavidin, which provides more time for longer viewing of labeled proteins and image capturing.