Double labeling with Alexa 488 and QD-streptavidin. Fixed and BSA-
blocked 3T3 cells were incubated sequentially with a mixture of ANA and
mouse anti-α-tubulin overnight at 4 with 3 biotinylated anti-
human IgG for 30 min, and then with a mixture of Alexa 488 conjugated to
anti-mouse IgG (68 nM; Molecular Probes) to label microtubules and red
QD-streptavidin (40 nM) to label the nucleus. Alternatively, after
overnight incubation with primary antibodies, cells were incubated with
goat anti-mouse IgG–biotin and then exposed to a mixture of 68 nM Alexa
488 conjugated to anti-human IgG (to label the nucleus) and 40 nM QD-
streptavidin (to stain microtubules).