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

Executive Summary: The Cy3 Goat Anti-Human IgG (H+L) Antibody (SKU K1208, APExBIO) is an affinity-purified, polyclonal secondary antibody conjugated to Cy3, offering excitation at 552 nm and emission at 565 nm (APExBIO). Its high specificity for human IgG and signal amplification properties make it a benchmark reagent in ICC/IF, IHC, flow cytometry, and ELISA workflows. The antibody is generated via goat immunization with pooled human immunoglobulins and is purified with antigen-coupled agarose beads, ensuring minimal cross-reactivity (see Zhao et al., 2025). The Cy3 fluorophore enables multiplexing and robust detection in complex biological samples. Proper storage (≤ −20°C, protected from light) maintains reagent integrity for up to 12 months.

Biological Rationale

Human IgG antibodies are pivotal in adaptive immunity, mediating pathogen neutralization, opsonization, and complement activation (Zhao et al., 2025). Reliable detection of human IgG is fundamental for immune monitoring, infectious disease research, and vaccine evaluation. Secondary antibodies, such as the Cy3 Goat Anti-Human IgG (H+L) Antibody, provide amplified signals by binding multiple epitopes on primary antibodies, thereby enhancing sensitivity in immunoassays (Illuminating Translational Immunology). The polyclonal nature ensures broad detection of diverse human IgG subclasses. Fluorophore conjugation (Cy3) enables quantitative and spatially resolved analyses in cellular and tissue contexts.

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

The Cy3 Goat Anti-Human IgG (H+L) Antibody is generated by immunizing goats with pooled human immunoglobulins, eliciting a polyclonal response targeting multiple IgG epitopes. The antibody is affinity-purified using human IgG-coupled agarose to minimize non-specific binding. The (H+L) designation indicates recognition of both heavy and light chains of human IgG, ensuring comprehensive detection. Cy3 fluorophore is covalently attached to the antibody, providing bright orange-red fluorescence (excitation: 552 nm; emission: 565 nm). Upon binding to a human IgG primary antibody, the Cy3-conjugated secondary amplifies the fluorescence signal, facilitating sensitive detection in immunoassays (Precision in Immunoassays). This mechanism is foundational for multiplexed detection and quantitative analysis.

Evidence & Benchmarks

• Demonstrated high specificity for human IgG, with negligible cross-reactivity to non-human immunoglobulins, as validated via immunoaffinity chromatography (see Table S2, Zhao et al., 2025).
• Cy3 conjugation yields robust fluorescence intensity (excitation: 552 nm; emission: 565 nm) with minimal photobleaching under standard immunofluorescence conditions (APExBIO product data).
• Validated for multiplexed detection in flow cytometry and IHC, providing linear quantitation over 3 log orders of analyte concentration (see Figure 4, Zhao et al., 2025).
• Optimal performance with 1 mg/mL stock, using 1–10 μg/mL working concentrations in PBS with 1% BSA and 0.02% sodium azide at room temperature (see protocol, Optimizing Immunoassays).
• Stability data support 12-month shelf-life at −20°C in 23% glycerol buffer, protected from light (APExBIO).

Applications, Limits & Misconceptions

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

• Immunocytochemistry/Immunofluorescence (ICC/IF): Enables subcellular localization of target proteins in human-derived cells using fluorescence microscopy (Elevating Immunoassay Precision).
• Immunohistochemistry (IHC): Compatible with both frozen (IHC-Fr) and paraffin-embedded (IHC-P) human tissue sections, enabling tissue architecture studies.
• Flow Cytometry: Permits multiplexed immunophenotyping, quantifying human IgG-bound cells with high sensitivity and reproducibility.
• ELISA: Used as a detection antibody for quantifying human IgG in serum or plasma samples, enabling high-throughput screening (Optimizing Cell-Based Assays).

Product limitations include lack of reactivity with non-human IgGs and potential signal quenching if exposed to prolonged light. Not suitable for direct detection of primary antibodies from species other than human or in the presence of endogenous goat IgG. For further assay troubleshooting, see the article Precision in Immunoassays, which focuses on comparative vendor performance. This dossier provides updated storage, cross-reactivity, and workflow parameters not covered in that article.

Common Pitfalls or Misconceptions

• Misuse as a primary antibody: The Cy3 Goat Anti-Human IgG (H+L) Antibody is a secondary reagent and cannot recognize antigens directly.
• Cross-reactivity with non-human samples: The antibody is affinity-purified for human IgG and shows negligible binding to mouse, rat, or other species' IgGs.
• Fluorophore instability: Cy3 fluorescence can be quenched by prolonged exposure to light or repeated freeze-thaw cycles; aliquoting and light protection are essential.
• Buffer incompatibility: Avoid sodium azide in buffers when using horseradish peroxidase (HRP)-based detection, but it is compatible with Cy3-based fluorescence.
• Multiplexing limitations: Cy3 emission overlaps with some red/orange fluorophores; spectral compensation is required for multicolor flow cytometry.

Workflow Integration & Parameters

• Sample Preparation: Use fixed, permeabilized cells/tissues. Block with 1% BSA in PBS to reduce non-specific binding.
• Antibody Dilution: Dilute Cy3 Goat Anti-Human IgG (H+L) Antibody to 1–10 μg/mL in blocking buffer. Incubate at room temperature for 30–60 min.
• Washing: Perform 3× washes with PBS to remove unbound antibody and minimize background fluorescence.
• Mounting/Detection: Use anti-fade mounting medium. Capture images or flow data promptly, using appropriate Cy3 settings (Ex 552 nm/Em 565 nm).
• Storage: Store antibody at 4°C (short-term, ≤2 weeks) or −20°C (long-term) in aliquots. Avoid more than 3 freeze-thaw cycles. Protect from light.

For workflow optimization and troubleshooting, Optimizing Cell-Based Assays presents real-world scenarios, whereas this article provides updated stability and spectral compensation guidelines.

Conclusion & Outlook

The Cy3 Goat Anti-Human IgG (H+L) Antibody from APExBIO sets a benchmark for reliable, sensitive, and multiplexed detection of human immunoglobulins in research and diagnostic workflows. Its validated specificity, robust fluorescence, and broad application range support translational immunology and infectious disease research, as underscored by recent orthopoxvirus antibody characterization studies (Zhao et al., 2025). Ongoing advances in fluorophore chemistry and antibody engineering will further enhance assay robustness and multiplexing capabilities. For detailed protocols and storage considerations, refer to the product page and linked technical resources.