What is Cytotoxicity?

Cytotoxicity is a general term that describes the detrimental effects of substances or environmental changes on cell health. Exposure of cells to a cytotoxic stimulus may compromise metabolic activity, inhibit cell growth or division or ultimately produce cell death. 'Necrotic' cell death is a catastrophic cell lysis. 'Apoptotic' cell death is a more controlled, programmed mechanism. 'Autophagy' is a specialised process whereby cells digest themselves from within. Irrespective of the mechanism of cytotoxicity, once a cell irreversibly loses its membrane integrity it is destined to die.

A number of cytotoxicity assays involve measurement of cell membrane integrity, either with vital dyes that are excluded from healthy cells, e.g. trypan blue or propidium iodide, or via the release of markers from dying cells (e.g. cellular proteases). Metabolic activity measurements, e.g. MTT, LDH or ATP assays are also used to measure cell health and viability. However, despite these methods, few if any involve direct counting of the number of dying cells over time.

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Video Introduction to Live-Cell Analysis for Cytotoxicity

See how live-cell analysis is used to visualize and quantify cell proliferation, identify specific subpopulations, and measure cell death.

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Introducing the Incucyte® Cytotoxicity Assay

The Incucyte® Live-Cell Analysis System enables real-time, automated cytotoxicity assays within your tissue culture incubator.

The Incucyte® Cytotoxicity Assay uses the Incucyte® Cytotox Dyes to make real time measurements of cell death based on cell membrane integrity, all within your incubator.

  • Incucyte® Cytotox Green Dye - labels dying cells green
  • Incucyte® Cytotox Red Dye - labels dying cells red

When added to the tissue culture growth medium, the Incucyte® Cytotox Dyes are inert, non-fluorescent and do not enter viable cells. As cells die and membrane integrity is lost, the Cytotox Dye enters the cell and fluorescently labels the nuclei. Dying cells are identified and quantified over time by the appearance of green- (or red) labelled nuclei. High definition phase contrast images and movies provide an additional validation of cell death based on morphology (e.g. loss of cytoskeleton structure, loss of motility).

Measure cytotoxicity in tumor, immune or neuronal cultures using the Incucyte® Cytotoxicity Assay. (Left) Real-time detection of cytotoxicity in HT-1080 fibrosarcoma cells following treatment with the cytotoxic drug camptothecin. Dying cells are labeled green, in real-time, by the mix-and-read Incucyte® Cytotox Green Dye. (Right) Incucyte® Cytotox Red Dye labels dead rat forebrain neurons treated with 333 μM glutamate.

Incucyte® Cytotoxicity Assay Concept

  1. Detect cytotoxicity in real-time by adding the mix-and-read Incucyte® Cytotox Dyes to your cultures
  2. Automatically quantify number of dying cells using intuitive Incucyte® live-cell imaging and analysis tools
  3. Multiplex cytotoxicity readouts with measurements of proliferation or apoptosis by combining with Incucyte® Nuclight nuclear labeling reagents, the Incucyte® Caspase 3/7 Dye, or the Incucyte® Annexin V Dye

Key Advantages of the Incucyte® Cytotoxicity Assay

Visualize and quantify cytotoxicity using time-lapse imaging

Observe cell death over time and measure cytotoxicity using intuitive Incucyte® integrated image analysis tools. Validate treatment effects with images and movies.

Figure 1. Visualize and validate cytotoxicity with images and movies. Time lapse images of SK-OV-3 ovarian cancer cell death in response to the anti-cancer drug camptothecin. Correlate fluorescent signal from the Incucyte® Cytotox Dyes with morphological changes associated with cell death. Quantify cytotoxicity using Incucyte® integrated image analysis tools. User-friendly software enables direct image-based detection of dying cells (pink mask).

Automatic analysis of the time course of cell death within your incubator

Determine how and when treatment effects occured without removing cells from the stable environment of the incubator - ideal for long-term studies (0 to <10 days).

Figure 2. Quantify treatment effects automatically and non-invasively.  Incucyte® Cytotoxicity Assay allows every well of a 96/384 well plate to be imaged and analyzed automatically to provide a microplate readout of cytotoxicity over time (left). Time-courses reveal concentration-dependent treatment effects (center). Transform data into concentration-response curves to compare pharmacology (right).

Simple mix-and-read 96/384-well protocols - no washing, no fixing, no lifting

Plate cells, add your treatments along with the Incucyte® Cytotoxicity Assay and Incucyte® Cytotox Dye and read kinetically in the IncuCyte® Live-Cell Analysis System. Read up to 6 x 384-well plates at once for medium/high-throughput screening.

View the Incucyte® Cytotoxicity Assay Protocol***[PDF LINK]

Figure 3. Adherent cell line protocol for the IncuCyte® Cytotoxicity Assay.

Multiplex with proliferation and apoptosis measurements

  • Combine Incucyte® Cytotoxicity Assays with Incucyte® Nuclight nuclear labeling reagents, Caspase-3/7 Dyes, or Annexin V Dyes for multiplexed measurements of proliferation/apoptosis. Readily discriminate between cytotoxic and cytostatic treatment effects.
  • Capture proliferation label-free, using Incucyte® Cell-by-Cell Analysis Software Module, thus enabling individual cell segmentation and classification based on fluorescence. Calculate the cytotoxic or apoptotic index within the Incucyte® software.

Figure 4. Multiplex cytotoxicity measurements with live-cell counting. Camptothecin (150 nM) treated HT-1080 fibrosarcoma cells (labeled with Incucyte® Nuclight Red Lentivirus) in the presence of the Incucyte® Cytotox Green Dye to detect live/dead cells over time.

Figure 5. Multiplex cytotoxicity measurements with live-cell label free counting and quantification of time-courses and concentration-dependence of cytotoxicity and proliferation. Camptothecin (1 µM) or cycloheximide (1 µM) treated HT-1080 fibrosarcoma cells in the presence of the Incucyte® Cytotox Green Dye to detect live/dead cells at 24h (masking of dead cells shown). Classification plots to identify green (dead) population (second column), time-course plots (third column) and concentration-response curves (forth column) show difference in effect of a cytotoxic and cytostatic compound.

Frequently Asked Questions

Yes, the interaction of cells in complex, tissue-like relationships can be studied in vitro with co-cultures, and cell death can be tracked in those co-cultures with markers of apoptosis and membrane integrity. For the most meaningful data, cell proliferation and cell death can be monitored at the same time in the same culture, with live-cell imaging.

To track a specific cell type throughout the co-culture experiment, start by transducing the cells with one of the NucLight reagents, ensuring that it is a different color than the Cytotox reagent used. The cells will grow and associate into dense, interacting cultures, and cell death will be monitored with the Cytotox or Caspase 3/7 reagents.

Note: All dead and dying cells will be positive for the Cytotox or Caspase 3/7 reagent, not just the ones transduced with the NucLight reagent.

The most commonly used method for predicting cell death in cytotoxicity assays is by using a reagent that is impermeant to intact lipid bilayers. Upon the onset of the cell death cascade, the lipid bilayer becomes porous and leaky, allowing the reagent into the cells where it stains the nucleus. Other assays are capable of detecting different stages and forms of cell death. Apoptosis assays detect the presence of certain markers of dying cells, like activated caspases and Annexin V.

View the cytotoxicity assay protocol
Learn more about apoptosis assays

The three assays you mentioned are not mutually exclusive. Cytotoxicity (or cytotox) assays could easily be measured alongside cell proliferation or cell migration assays. The only factors to keep in mind are that you'll need to have enough imaging channels to monitor the readouts from all of the assays at the same time. For live-cell imaging with the IncuCyte that means you could track cell confluence (which needs no fluorochrome), chemotaxis (in either the red or green channel), and cytotoxicity (in the remaining channel).

They reduce human variance as they take care of aspiration and dispensing. Their multiple pipetting modes speed up work. Also electronic pipettes offer security features, like calibration reminders and password protection for saved programs.

The range of cytotoxicity assays is very broad, so it's impossible to provide an answer that applies to all cytotox assay methods. However, for methods that involve a visual-recognition component alongside a fluorescent intensity component, it is possible to differentiate between a number of cells undergoing apoptosis and a single cell lysing. Specific apoptosis assays, when multiplexed, can even provide finer detail, including signaling the onset of the apoptotic cascade or the derangement of the lipid membrane. Assays like ELISAs, where signal is entirely cumulative, could not provide details like these.

A common reason for this problem is continued cell growth throughout the cell death assay, leading to overcrowding in the well. When plating your cells for cytotoxicity assays, make sure to have an exact count, and don't seed so many cells that your cells will become contact inhibited (by reaching 100% confluence) before your endpoint.

Occasionally, cytotoxic substances can have the paradoxical effect of stimulating cell proliferation at sublethal concentrations. If you routinely see this effect with your combination of cells and cytotoxic agent, this may be the explanation.

Ordering Information

Ordering Information

Incucyte® Cytotox Dyes are fully validated for use with the Incucyte® Live-Cell Analysis System and cytotoxicity assays. Furthermore, they can be combined with our range of Incucyte® Nuclight nuclear labeling reagents, the Incucyte® Caspase 3/7 Dye, or the Incucyte® Annexin V Dye for multiplexed measurements of proliferation and apoptosis alongside cytotoxicity in a single well.


Product Data Sheet

Safety Data Sheet


Cat. No.

Incucyte® Cytotox Red Dye for counting dead cells



5 μL x 5


Incucyte® Cytotox Green Dye for counting dead cells



5 μL x 5


Incucyte® Cytotox NIR Dye for counting dead cells



100 µl


Incucyte® Caspase 3/7 Green Dye for Apoptosis



20 µl


Incucyte® Annexin V Red Dye for Apoptosis



100 tests


Incucyte® Annexin V Green Dye for Apoptosis



100 tests


Incucyte® NucLight Rapid Red Dye for nuclear labeling



50 µL


Incucyte® Caspase 3/7 Red Dye for Apoptosis



20 µL


Incucyte® Cell-by-Cell Analysis Software Module



1 module



Literature and Documentation

Incucyte® Cell Health and Viability Assays Brochure

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Quantification of Cytotoxicity Using the Incucyte® Cytotoxicity Assay

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Incucyte® Cytotox Dyes For Detection of Cell Membrane Integrity D...

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SFN 2016 Poster

Quantitative, real-time live-cell analysis method and reagents for evaluation of cell health in neuronal cultures 

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Cell Proliferation

Cell proliferation is the biological process of cells increasing in number over time through cell division ('mitosis' in eukaryotic cells).

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Apoptosis is an essential process for normal tissue development and homeostasis by which cells undergo timely programmed cell death.

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Cell-by-Cell Analysis

Quantify the process and effects of cellular heterogeneity in real-time in living cells – inside your incubator.

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