What is the fluorescence excitation and emission maxima of Alexa Fluor 647 dye?
Alexa Fluor 647 has an excitation/emission maxima of 650/670 nm.
Find additional tips, troubleshooting help, and resources within our Cell Analysis Support Center.
I will be performing a cell proliferation assay using Click-iT EdU kit. At what point can I stop overnight, or do I have to perform all the steps continuously?
One may store the sample after fixation overnight in PBS at 4oC. For longer storage (<1 week) , store in buffer with 1-2% formaldehyde or in formalin to limit microbial growth. If you use sodium azide as a microbial inhibitor, it must be completely removed prior to the Click-iT reaction.
Find additional tips, troubleshooting help, and resources within our Cell Viability, Proliferation, Cryopreservation, and Apoptosis Support Center.
I need to test cells for apoptosis after they have been formaldehyde-fixed and permeabilized. What dye or conjugate do you recommend? Will Annexin V conjugates work?
We do not recommend Annexin V for post-fix labeling, since fixation inactivates the function of the translocase; fixed samples would show mostly uniform labeling with Annexin V. The only options you have for apoptosis assays after fixation are to use an anti-caspase antibody or perform a TUNEL assay, such as with the Click-iT TUNEL Imaging kits.
Find additional tips, troubleshooting help, and resources within our Cell Analysis Support Center.
Can I use Click-iT Plus TUNEL Assay Kits for In Situ Apoptosis Detection (Cat. Nos. C10617, C10618, C10619) for whole mount immunofluorescence staining of zebrafish larvae?
Yes. The Click-iT Plus TUNEL Assay Kits for In Situ Apoptosis Detection (Cat. Nos. C10617, C10618, C10619) is optimized for use with tissues and should work on zebrafish larvae, although it has not been internally validated with zebrafish larvae.
Find additional tips, troubleshooting help, and resources within our Cell Viability, Proliferation, Cryopreservation, and Apoptosis Support Center.
I am observing no signal or very low specific signal for my click-labeled samples. What can I do to improve the signal?
The click reaction is only effective when copper is in the appropriate valency. Azides and alkynes will not react with each other without copper. Make sure that the click reaction mixture is used immediately after preparation when the copper (II) concentration is at its highest.
Do not use additive buffer that has turned yellow; it must be colorless to be active.
Cells need to be adequately fixed and permeabilized for the TdT enzyme and click reagents to have access to the nucleus. Tissue samples require digestion with proteinase K or other proteolytic enzymes for sufficient TdT access.
Some reagents can bind copper and reduce its effective concentration available to catalyze the click reaction. Do not include any metal chelator (e.g., EDTA, EGTA, citrate, etc.) in any buffer or reagent prior to the click reaction. Avoid buffers or reagents that include other metal ions that may be o xidized or reduced. It may be help to include extra wash steps on the cell or tissue sample before performing the click reaction.
You can repeat the click reaction with fresh reagents to try to improve signal. Increasing the click reaction time longer than 30 minutes will not improve a low signal. Performing a second, 30 minute incubation with fresh click reaction reagents is more effective at improving labeling.
Your cells may not be apoptotic. Prepare a DNase I-treated positive control to verify that the TdT enzymatic reaction and click labeling reaction are working correctly.
Find additional tips, troubleshooting help, and resources within our Labeling Chemistry Support Center.