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I have always used Dextrans (10,000 MW) or BSA (TMR or Alexa Fluor647
Labeled) on both cells and C. elegans for the following reasons:

1. they are non-toxic
2. Last for days - (4-5 days)
3. very photostable

Of course the caveat is that they are taken into the lysosomes via the
endocytic pathway and require a chase (>4 hours) after labeling to ensure
endosomes are not labelled as well. I get great colocalisation with
cathepsin L and other lysosomal enzymes.

Hope this helps, 

Cliff

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