Invitrogen™ CellROX™ Reagent for oxidative stress detection

H₂DCFDA and similar derivatives are not fixable. The same goes for dihydroethidium and dihydrorhodamine. However, CellROX Deep Red and CellROX Green are retained for a limited time upon fixation with formaldehyde. CellROX Green may be retained upon subsequent Triton X-100 permeabilization. Avoid the use of any acetone or alcohol-based fixatives or fixatives that include alcohol, such as formalin.

CellROX Green dye diluted in a DMSO stock solution is stable for multiple freeze-thaw cycles, but it is not stable long-term in aqueous solution. Please note, every time the stock solution is opened, some of the dye can oxidize, which will increase background noise. DMSO readily absorbs moisture from the air, especially when cold, so be sure to completely thaw the stock solution to room temperature before opening and only open briefly. Water in the DMSO will gradually cause the dye to precipitate and come out of solution. Minimize the number of times you use a stock solution to several freeze-thaw cycles or make small aliquots to reduce the number of freeze-thaw cycles.

The main difference between the CellROX Green Flow Cytometry Assay Kit (Cat. No. C10492) and CellROX Green Reagent, for oxidative stress detection (Cat. No. C10444), is the suggested final working concentrations and application. The CellROX Green in the CellROX Green Flow Cytometry Assay Kit is specifically designed for flow cytometry analysis and is used at a lower concentration than what is required for imaging, as fluorescence-activated cell sorting (FACS) is a very sensitive detection system.

The standalone CellROX Green Reagent (Cat. No. C10444) is marketed for fluorescent microscopy and require working concentrations appropriate for imaging. This can typically be as much as 10-fold higher than the concentration recommended for flowcytometry. The standalone CellROX Green Reagent can also be used for flowcytometry; however, the working concentration will have to be optimized. For the flow cytometry quick reference, use the link below.

CellROX Flow Cytometry Assay Kit Quick Reference

Many dyes that are used on mammalian cells have also been shown to be useful in bacterial cells. For example, CellROX Deep Red Reagent has been shown to work in B. subtilis (see Reference: http://www-brs.ub.ruhr-uni-bochum.de/netahtml/HSS/Diss/RaatschenNadja/diss.pdf). If you are interested in a particular dye, but are not sure if it will work on your bacteria, literature searches are the best way to check to see if it has been tested. If not, then it may be worth testing yourself.

First, make sure you have both a negative (untreated) and positive (ROS-induced) sample to compare. A good positive control can be the use of 100 µM menadione for one hour or 50 µM nefazodone for 24 hours. H2O2 can also be used, though it does not work well for CellROX dyes. Some dyes, such as H2DCFDA, require esterase cleavage, so don't incubate in the presence of serum (which contains esterases that can prematurely cleave the dye). If your positive control does not show significant change compared to the negative control, try increasing the concentration and label time for the dye. Our manuals give starting recommendations. Be sure to image your live cells as soon as possible. Only two dyes (CellROX Green and CellROX Deep Red) are retained with formaldehyde fixation. Finally, make sure you are using filters and instrument settings to match the excitation and emission spectra of the dye.