I'm labeling live cells with Vybrant DiI or DiD lipophilic cyanine dyes. DiI gives a nice even membrane labeling, but DiD is more "spotty". What can be done?
This is expected. DiD (which is far-red fluorescent) is never as uniform as DiI (which is orange fluorescent). If uniformity is desired, try increasing the label time and concentration, but it still isn't likely to be as uniform as DiI. CellMask Deep Red Plasma Membrane stain is much more uniform and is about the same wavelength as DiD. However, if you intend to do cell tracking over days, CellMask stain has not been tried for that application.
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I stained my cells with a lipophilic cyanine dye, like DiI, but the signal was lost when I tried to follow up with antibody labeling. Why?
Since these dyes insert into lipid membranes, any disruption of the membranes leads to loss of the dye. This includes permeabilization with detergents like Triton X-100 or organic solvents like methanol. Permeabilization is necessary for intracellular antibody labeling, leading to loss of the dye. Instead, a reactive dye such as CFDA SE should be used to allow for covalent attachment to cellular components, thus providing for better retention upon fixation and permeabilization.
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How long does it take for lipophlic tracers to transport along the membrane? How much faster are the FAST lipophilic dyes?
The transport is fairly slow, around 6 mm/day in live tissue and slower in fixed tissue, so diffusion of lipophilic carbocyanine tracers from the point of their application to the terminus of a neuron can take several days to weeks The FAST DiO and DiI analogs (which have unsaturated alkyl tails) can improve transport rate by around 50%.
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Which form of the lipophilic tracers (DiO, DiI, DiD, etc) should I use?
Select the dye that is compatible with your available excitation source(s) and emission filter set/channels. The solid, paste and crystal forms can be applied directly to neurons in tissues. For labeling cells in culture or microinjection, the lipophilic dyes in solution or solid form can be used.
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I want to label two cell populations and then perform a cell fusion assay. Which reagents are best for imaging this?
Lipophilic cyanine dyes are preferred for this sort of assay, since they insert into cellular membranes and then, upon fusion, are shared by the fused cells as the membranes are shared. For example, one cell population can be labeled with DiI (orange-red) and another cell population can be labeled with DiO (green), and when the cells fuse, the combined color appears yellow (when imaged with a dual-bandpass filter set).
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