Cy3 Goat Anti-Human IgG (H+L) Antibody: Precision Detection in Immunoassays

Executive Summary: The Cy3 Goat Anti-Human IgG (H+L) Antibody (SKU: K1208) is an affinity-purified, polyclonal secondary antibody designed for sensitive detection of human immunoglobulins. It is conjugated with Cy3, a fluorophore characterized by excitation at 552 nm and emission at 565 nm, providing robust signal amplification in fluorescence-based assays (Zhao et al., 2025). The antibody is validated for key applications such as immunofluorescence (IF), immunohistochemistry (IHC), flow cytometry, and ELISA. APExBIO supplies the product as a 1 mg/mL liquid in a stabilizing buffer, ensuring 12 months of stability at -20°C. The reagent is widely cited for its role in translational immunology, including orthopoxvirus research (Illuminating Translational Immunology).

Biological Rationale

Secondary antibodies such as the Cy3 Goat Anti-Human IgG (H+L) Antibody are essential for detecting, sorting, and quantifying human immunoglobulins in research and clinical diagnostics. Their use enables the visualization and amplification of antigen-antibody interactions, which is critical for sensitive immunoassays (Zhao et al., 2025). The goat-derived polyclonal format ensures broad epitope recognition across the heavy and light chains (H+L) of human IgG, maximizing assay sensitivity. Fluorescent conjugation with Cy3 allows multiplexing and direct visualization under standard fluorescence microscopy setups. Amplified detection is especially valuable in workflows targeting low-abundance analytes or assessing neutralizing antibody responses in infectious disease studies, such as those involving orthopoxvirus or SARS-CoV-2 (Illuminating Translational Immunology).

Mechanism of Action of Cy3 Goat Anti-Human IgG (H+L) Antibody

This antibody is generated by immunizing goats with pooled human immunoglobulins, followed by immunoaffinity purification using antigen-coupled agarose beads. The resulting polyclonal antibodies are conjugated to Cy3, a sulfoindocyanine fluorophore with a peak excitation at 552 nm and emission at 565 nm (APExBIO product page). Upon binding to primary human IgG antibodies, the Cy3-conjugated secondary amplifies the detection signal via multiple binding events (signal amplification). Cy3's photostability and high quantum yield support clear, quantifiable fluorescence signals. The antibody specifically targets both heavy and light chains of human IgG, rendering it compatible with diverse primary antibody isotypes and subclasses.

Evidence & Benchmarks

• Affinity-purified polyclonal goat anti-human IgG (H+L) exhibits broad epitope coverage, increasing sensitivity in immunodetection assays (Zhao et al., 2025).
• Cy3 conjugation provides stable, bright fluorescence with excitation/emission maxima at 552/565 nm, compatible with standard filter sets (APExBIO product page).
• Validated for ICC/IF, IHC (frozen and paraffin-embedded), flow cytometry, and ELISA at 1 mg/mL concentration in PBS/23% glycerol/1% BSA/0.02% sodium azide buffer (Optimizing Immunoassays).
• Stability is maintained for 12 months at -20°C with protection from light; repeated freeze-thaw cycles reduce signal intensity (APExBIO product page).
• Signal amplification is observed due to multivalent binding: multiple secondary antibodies can bind a single primary, enhancing assay linearity and sensitivity compared to directly labeled primaries (Precision Immunofluorescence).

Applications, Limits & Misconceptions

The Cy3 Goat Anti-Human IgG (H+L) Antibody is validated for:

• Immunocytochemistry/Immunofluorescence (ICC/IF): Enables visualization of human IgG in cultured cells with Cy3 fluorescence (Optimizing Immunoassays).
• Immunohistochemistry (IHC): Suitable for both frozen and paraffin-embedded tissue sections, supporting broad histological profiling.
• Flow Cytometry: Detects surface-bound or intracellular human IgG by Cy3 fluorescence, compatible with standard flow cytometers.
• ELISA: Provides bright, quantifiable fluorescence for endpoint or kinetic detection.

The antibody is not suitable for direct primary detection, cannot distinguish human Ig subclasses (without primary specificity), and may cross-react with non-human primates due to sequence homology. For a deeper exploration of mechanistic versus translational utility, see From Mechanism to Medicine, which this article extends by benchmarking stability and application scope.

Common Pitfalls or Misconceptions

• Not for direct antigen detection: Requires human IgG as primary antibody target.
• Photobleaching: Cy3 signal degrades with prolonged light exposure; always protect from light.
• Species cross-reactivity: May bind non-human primate IgG; verify specificity for non-human samples.
• Buffer incompatibility: Avoid using sodium azide in live cell assays due to cytotoxicity.
• Signal loss from repeated freeze-thaw: Aliquot to minimize freeze-thaw cycles.

Workflow Integration & Parameters

For optimal results, dilute the antibody as recommended (typically 1:100–1:1000 for IF/IHC; 0.1–1 μg/mL for flow cytometry and ELISA). Store at 4°C for up to 2 weeks or at -20°C for long-term stability. Use aliquots to avoid freeze-thaw cycles and always protect from light. The supplied buffer (PBS, 23% glycerol, 1% BSA, 0.02% sodium azide) stabilizes the antibody, but sodium azide is unsuitable for live-cell staining. The product is shipped at 4°C and should be equilibrated to room temperature before use. For detailed real-world workflow strategies and troubleshooting, see Optimizing Cell-Based Assays, which this article updates by adding current evidence benchmarks and stability guidance.

Conclusion & Outlook

The Cy3 Goat Anti-Human IgG (H+L) Antibody from APExBIO is a validated, high-performance secondary antibody for detecting human immunoglobulins in diverse immunoassays. Its robust signal amplification, broad application, and stable Cy3 fluorescence make it a reference standard for translational research, including orthopoxvirus antibody characterization (Zhao et al., 2025). Ongoing advances in antibody therapeutics and detection platforms underscore the continued relevance of optimized fluorescent secondary antibodies. For the complete product specification and ordering, visit the Cy3 Goat Anti-Human IgG (H+L) Antibody product page.