CytoTrace Red CMTPX Staining Protocol & Usage Guide

CytoTrace Red CMTPX is a cell-permeant, chloromethyl-based fluorescent dye that covalently labels cytoplasmic components to enable robust long-term tracking of live cells across multiple generations.

Product SKU

C1452254

Also Known As

CMTPX; CellTracker Red CMTPX analog

Excitation / Emission

Approximately 577 nm excitation / 602 nm emission (red channel)

Cell Permeability

Cell-permeant; freely crosses plasma membrane

Labeling Mechanism

Chloromethyl group reacts covalently with intracellular thiols to retain dye in viable cells

Compatible Applications

Cell migration, invasion assays, co-culture tracking, flow cytometry, fluorescence microscopy

Principle and Mechanism of Action

CytoTrace Red CMTPX belongs to the chloromethyl (CM) family of cell-permeant fluorescent tracers. Upon passive diffusion into live cells, the reactive chloromethyl moiety forms covalent thioether bonds with intracellular glutathione and other low-molecular-weight thiols. This covalent attachment anchors the dye within the cytoplasm and prevents significant leakage into neighboring cells or the extracellular medium, making it well suited for multi-generation cell tracking studies.

The dye fluoresces in the red spectral range (excitation ~577 nm, emission ~602 nm), allowing simultaneous use with green-channel probes (e.g., GFP, calcein AM) in multi-color experiments. Because retention depends on cellular thiol content and metabolic activity, CytoTrace Red CMTPX also serves as an indirect indicator of cell viability; dead or membrane-compromised cells fail to retain the dye effectively.

Materials and Reagent Preparation

Required materials:

• CytoTrace Red CMTPX (SKU: C1452254)
• Dimethyl sulfoxide (DMSO), anhydrous, cell-culture grade
• Phosphate-buffered saline (PBS), pH 7.4, prewarmed to 37 °C
• Serum-free cell culture medium, prewarmed to 37 °C
• Complete growth medium for recovery incubation
• Fluorescence microscope or flow cytometer equipped with a 561 nm (or 543/555 nm) laser/filter set

Stock solution preparation: Reconstitute the lyophilized or solid CMTPX powder in anhydrous DMSO to prepare a 10 mM stock solution. Vortex briefly and ensure complete dissolution. Aliquot into single-use volumes, protect from light, and store at −20 °C. Avoid repeated freeze–thaw cycles. Confirm the exact recommended concentration on the Certificate of Analysis supplied with the product, as lot-specific guidance takes precedence.

Working solution preparation: Dilute the stock solution in prewarmed serum-free medium to a working concentration typically in the range of 1–25 µM. Serum-containing medium should be avoided during the staining step because serum proteins may sequester the dye before it enters cells.

Step-by-Step Staining Protocol

1. Cell preparation: Culture cells to 50–80% confluency in appropriate vessels. For adherent cells, wash twice with prewarmed PBS to remove serum.
2. Staining: Remove PBS and add sufficient prewarmed working solution to cover the cell monolayer (e.g., 1 mL per well of a 6-well plate). Incubate at 37 °C, 5% CO₂ for 15–45 minutes, protected from light. Optimize incubation time and dye concentration empirically for each cell type.
3. Wash: Aspirate the staining solution and wash cells twice with prewarmed PBS to remove unincorporated dye.
4. Recovery incubation (recommended): Add complete growth medium (containing serum) and incubate for an additional 15–30 minutes at 37 °C. This step allows non-covalently bound dye to diffuse out, improving signal-to-background ratio and ensuring only covalently retained dye remains.
5. Imaging or assay: Cells are now ready for fluorescence microscopy, flow cytometry, or downstream functional assays. For live-cell imaging, maintain cells in appropriate live-cell imaging buffer or medium at 37 °C.
6. Long-term tracking: Labeled cells can be maintained in culture for extended periods. Monitor fluorescence intensity over time; signal will dilute with each cell division, which can be exploited to estimate proliferation rate.

Note: All steps should be performed under subdued light to minimize photobleaching of the dye.

Troubleshooting and Optimization Tips

Problem	Likely Cause	Suggested Solution
Weak or no fluorescent signal	Dye concentration too low; inadequate incubation time; degraded stock	Increase working concentration within tested range; extend incubation; prepare fresh stock in dry DMSO
High background / diffuse signal in medium	Insufficient washing; serum present during staining	Perform additional PBS washes; ensure serum-free medium is used during staining step
Rapid signal loss after labeling	Cells have low thiol content; non-viable cells	Confirm cell viability before staining; include recovery incubation step; verify storage conditions of dye
Cytotoxicity observed	Working concentration too high or incubation too long	Reduce concentration and/or incubation time; validate with viability assay (e.g., Trypan blue exclusion)
Spectral bleed-through in multi-color panel	Emission overlap with green-channel probes	Apply spectral compensation; use appropriate bandpass filters; consider sequential acquisition

Storage, Safety and Handling

Storage: Store the neat compound and DMSO stock solutions at −20 °C, protected from light and moisture. Under recommended storage conditions, the reagent is expected to be stable for at least 12 months from the date of receipt; consult the product Certificate of Analysis for lot-specific expiry information. Reconstituted working solutions should be prepared fresh on the day of use and not stored.

Handling precautions: CytoTrace Red CMTPX is intended for in vitro research use only and is not approved for use in humans or animals. As with all reactive fluorescent dyes, avoid prolonged skin and eye contact. Wear appropriate personal protective equipment (gloves, lab coat, eye protection) when handling. DMSO enhances dermal penetration of dissolved compounds; exercise additional caution when preparing stock solutions.

Disposal: Dispose of waste reagent and contaminated materials in accordance with local institutional and governmental regulations for chemical waste.

Frequently asked questions

What is the recommended working concentration of CytoTrace Red CMTPX for most mammalian cell lines?

Working concentrations typically range from 1 to 25 µM, with 5–10 µM being a common starting point for many adherent mammalian cell lines. Optimal concentration should be determined empirically for each cell type by balancing signal intensity against potential cytotoxicity.

Can CytoTrace Red CMTPX be used for flow cytometry in addition to fluorescence microscopy?

Yes, CytoTrace Red CMTPX is compatible with flow cytometry. Use an instrument equipped with a 532 nm, 543 nm, or 561 nm laser and an appropriate bandpass filter in the 590–620 nm range to detect the red emission. Ensure cells are maintained as a single-cell suspension and processed promptly after labeling.

How long can labeled cells be tracked after staining with CytoTrace Red CMTPX?

Because the dye is covalently retained within the cytoplasm, labeled cells can generally be tracked for several days under standard culture conditions. However, fluorescence intensity will decrease with each cell division due to dye dilution among daughter cells, so the practical tracking window depends on the proliferation rate of the cell type under study.

Is a recovery incubation step mandatory after washing?

The recovery incubation (15–30 minutes in complete medium) is strongly recommended rather than strictly mandatory. It allows non-covalently associated dye molecules to diffuse out of cells, significantly reducing background fluorescence and improving the specificity of the retained signal. Skipping this step may result in higher non-specific background.

Can CytoTrace Red CMTPX be used simultaneously with GFP-expressing cells?

Yes, the red emission of CytoTrace Red CMTPX (~602 nm) is spectrally distinct from GFP emission (~509 nm), making it well suited for dual-color experiments with GFP-labeled cells. Appropriate bandpass filters and spectral compensation should be applied to minimize any residual bleed-through between channels.

References

1. Haugland RP. Handbook of Fluorescent Probes and Research Products, 10th ed. Molecular Probes/Invitrogen; 2005. (General reference for chloromethyl cell-permeant tracers.)
2. Invitrogen/Thermo Fisher Scientific. CellTracker Dyes for Long-Term Tracing of Living Cells — Product Information Sheet. (Canonical protocol reference for CMTPX-class reagents.)
3. Bhanu Prashanth GK, et al. Use of fluorescent cell tracers to monitor lymphocyte migration in vivo and in vitro. J Immunol Methods. (Representative application reference — specific authors and volume need verification.)

Products are supplied for research and development use only. Not for use in humans, animals, diagnosis, or therapy.