Overview
Calcein AM is a vital fluorescent probe in biomedical research, designed to assess cell viability and membrane integrity. As a lipophilic, non-fluorescent compound, it passively diffuses into cells and is hydrolyzed by intracellular esterases to yield brightly fluorescent calcein. This conversion occurs only in live cells with active esterase activity, making it a reliable indicator of cell health. Its compatibility with high-throughput systems and multiplex assays has solidified its role in drug discovery and toxicology studies. The dye’s acetoxymethyl (AM) ester groups mask its polar carboxylates, enabling membrane permeability. Upon cleavage, the trapped calcein emits green fluorescence, detectable by standard FITC filters. This mechanism avoids the need for cell fixation or lysis, allowing real-time monitoring of dynamic cellular processes.
Physical and Chemical Properties
Calcein AM appears as an orange-red crystalline powder with limited solubility in aqueous solutions but dissolves readily in organic solvents like dimethyl sulfoxide (DMSO). Its fluorescence activation depends on esterase-mediated hydrolysis, which releases calcein with peak excitation at 494 nm and emission at 517 nm. The dye exhibits minimal photobleaching and retains stability for hours post-loading, ideal for prolonged imaging sessions. Chemically, the AM ester groups confer stability in storage but are labile to enzymatic cleavage. The product’s performance can vary with factors like esterase activity levels, incubation time (typically 15–30 minutes at 37°C), and dye concentration (0.1–10 µM). Optimal results require titration to balance signal intensity and potential dye toxicity.
Main Applications
Calcein AM is a cornerstone in cell-based assays, primarily for viability testing in pharmaceutical screens and cancer research. It distinguishes live cells from dead ones (often combined with ethidium homodimer-1 for dual staining) in cytotoxicity models. Its non-disruptive nature enables longitudinal studies, such as tracking cell migration in wound-healing assays or monitoring stem cell differentiation. In industrial settings, the dye validates sterilization processes by confirming microbial lethality. Flow cytometry applications leverage its uniform staining to quantify viable cell populations. Recent adaptations include microfluidics-based organ-on-chip systems, where real-time viability data enhances mechanistic studies.
Safety and Storage
While Calcein AM itself is low-risk, precautions are necessary during handling due to its DMSO solubility. Use in a fume hood with nitrile gloves to prevent skin contact. Post-hydrolysis, the fluorescent product is non-toxic and biodegradable, aligning with standard laboratory waste protocols. Long-term storage demands anhydrous conditions at -20°C in sealed, light-proof containers. Repeated freeze-thaw cycles degrade performance; aliquot stock solutions (e.g., 1–10 mM in DMSO) for single-use. For consistent results, verify dye activity with control cells before large-scale experiments.
B2B Procurement Guide
Bulk buyers should prioritize suppliers with ISO 13485 certification for consistent quality. Key specifications include HPLC purity (>90%), low heavy metal content, and absence of free calcein (impurity). Batch-specific certificates of analysis (CoA) are mandatory for regulatory compliance in GLP studies. Pricing scales with volume; negotiate contracts for 100 mg+ quantities. Consider lyophilized formats for reduced shipping costs. Alternative vendors (e.g., Thermo Fisher, Sigma-Aldrich, BioLegend) offer competitive formulations, but validate equivalency via pilot tests. Lead times may extend for GMP-grade material.
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