Name: Acid Red 91 (Highly Pure)
Brand: Molecular Depot
SKU: B2018405
Price: 595.00 USD
Availability: InStock

<h2 data-section-id="gmblv6" data-start="0" data-end="33">What are cell stains and dyes?</h2>
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Cell stains and dyes are fluorescent or colorimetric reagents that label cells or cellular components to enable visualization, quantification, or viability assessment. Common categories include live/dead viability dyes (trypan blue, calcein AM/ethidium homodimer combinations), nuclear stains (DAPI, Hoechst), organelle-selective dyes (mitochondrial, lysosomal, lipid stains), and cell-tracking dyes (carbocyanine-based membrane labels). Related entities include flow cytometry gating, fluorescence channels (FITC, TRITC, Cy5), high-content imaging, apoptosis and necrosis assays, and cell proliferation monitoring.
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<h2 dir="ltr">What you'll find in this category: </h2>
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Organelle-Specific Stains: Target-selective dyes designed to cleanly isolate nuclei, mitochondria, membranes, or cytoskeletal networks.
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Viability Indicator Dyes: Colorimetric and fluorescent metabolic markers engineered to differentiate live, dying, or necrotic cell populations.
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Classic Histological Stains: Time-tested chemical dyes optimized for definitive tissue morphology assays, counterstaining protocols, and pathology reviews. 
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<h2 data-section-id="1o0zxdz" data-start="834" data-end="871">How to choose cell stains and dyes</h2>
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Viability dye chemistry
Trypan blue remains the standard for manual hemocytometer cell counting based on membrane impermeability in dead cells, while fluorescence-based live/dead kits (e.g., calcein AM for live cells paired with a membrane-impermeable dead-cell stain) are preferred for flow cytometry and imaging workflows that require higher throughput or multiplexing.
Fluorescence channel compatibility
Match the dye&rsquo;s excitation/emission spectrum to the available channels on the flow cytometer or imaging system (FITC, TRITC, Cy5, and others). When multiplexing multiple stains, check for spectral overlap to avoid signal bleed-through between channels.
Live-cell vs fixed-cell compatibility
Some dyes (such as long-term live-cell tracking dyes) are designed for extended imaging without cytotoxicity, while others (such as many nuclear stains) require fixation and/or permeabilization. Confirm live-cell compatibility if the experiment continues after staining.
Cell-tracking dye retention and dilution
Carbocyanine-based membrane dyes (e.g., PKH-type dyes) are diluted with each cell division, making them suitable for proliferation and migration tracking over a limited number of generations. They are less suitable for long-term lineage tracking across many passages, so confirm expected experimental duration against dye retention characteristics.
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<h2 data-section-id="1fljvas" data-start="3171" data-end="3196">Specifications context</h2>
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Fluorescent dyes are defined by excitation and emission wavelength pairs (for example, FITC-range dyes around ~495/515 nm). Viability assays often include reference controls to define live versus dead populations and ensure consistent gating in flow cytometry or imaging workflows. Pack sizes for academic labs range from single-use kits to bulk reagent formats sufficient for hundreds of assays, with cell-tracking dyes typically provided per labeling set or per vial.
This category sits within MBP's cell culture reagents catalog. Labs performing 3D culture or spheroid viability assays may also review organoids, spheroids, and 3D cell culture reagents, while those combining imaging with receptor or pathway analysis can consult receptors and modulators for linked signaling studies. MBP's specialist team can help match dye spectral properties with existing flow cytometry or imaging system configurations before order placement.
Looking to optimize your multi-color imaging panels or match a specific laser line? Drop a message to the MBP desk, and we'll help you lock in the ideal dye pairings.

Cell Stains & Dyes

Molecular Depot

Key Specifications

Acid Red 91 (Highly Pure)

Acid Red 91, catalog B2018405, is a xanthene dye (also known as eosin B), with typical uses including histological counterstain and dye research. Available from MBP, a registered vendor at leading US research institutions.