Cy5.5 NHS Ester (Non-Sulfonated): Driving Precision in Near-Infrared Fluorescence Imaging

Principle and Setup: The Power of Near-Infrared Fluorescent Protein Conjugation

Cy5.5 NHS ester (non-sulfonated) is a high-performance near-infrared fluorescent dye specifically engineered for covalent labeling of biomolecules with primary amines. Its chemical structure features an N-hydroxysuccinimide (NHS) ester group, which reacts efficiently with amino groups on peptides, proteins, and oligonucleotides to form stable amide bonds. The dye's absorption (excitation) maximum at 684 nm and emission maximum near 710 nm enable deep-tissue imaging with minimal background interference, a decisive advantage for in vivo fluorescence imaging and optical imaging of tumors. According to the product information, Cy5.5 NHS ester (non-sulfonated) delivers a high extinction coefficient of 209,000 M⁻¹cm⁻¹ and a quantum yield of 0.2, supporting robust fluorescence output for sensitive detection even at low target concentrations.

The dye's solubility profile is optimized for conjugation: it dissolves readily in DMF or DMSO (≥35.82 mg/mL in DMSO), but is poorly soluble in water, necessitating an initial dissolution in organic solvent before introduction to aqueous labeling buffers. This property, combined with its photostability and long shelf-life (24 months at -20°C, protected from light), makes Cy5.5 NHS ester a staple in translational and preclinical imaging workflows.

Step-by-Step Workflow for Protein and Nanoparticle Labeling

For researchers deploying Cy5.5 NHS ester (non-sulfonated) in experimental protocols, optimizing conditions is critical for maximizing labeling efficiency and preserving biomolecule function. Below is a streamlined workflow with practical enhancements derived from leading references and validated by APExBIO users.

Protocol Parameters

• Dye stock preparation: Dissolve Cy5.5 NHS ester (non-sulfonated) to 10 mM in anhydrous DMSO. Prepare fresh aliquots immediately before use to avoid hydrolysis.
• Protein/peptide labeling: Mix protein (1–5 mg/mL) in 0.1 M sodium bicarbonate buffer, pH 8.3, with dye at a final molar ratio of 3:1 (dye:protein). Incubate for 1 hour at room temperature, shielded from light.
• Purification: Remove unreacted dye by gel filtration (e.g., Sephadex G-25 column) or dialysis (cutoff ≥10 kDa) against PBS for 2–4 hours at 4°C.

These conditions align with best practices highlighted in workflow guides and protocol optimization resources, which stress the importance of careful buffer selection (avoiding amine-containing buffers like Tris) and rapid dye usage after stock preparation.

Advanced Applications: From Tumor Imaging to Ultrasound-Responsive Nanoplatforms

Cy5.5 NHS ester (non-sulfonated) empowers a spectrum of advanced applications, from classic protein labeling to the latest nanotechnology-enabled imaging. Its near-infrared emission is particularly suited for in vivo fluorescence imaging, as demonstrated in translational oncology and neuroscience. For example, in recent tumor delineation studies, Cy5.5-labeled antibodies enabled precise, real-time visualization of tumor margins in live animal models, outperforming visible-wavelength dyes in signal-to-noise and imaging depth.

The dye’s compatibility with nanoparticles and polymers further extends its utility. In the context of the reference study, piezoelectric nanoplatforms were precisely tracked in vivo using near-infrared fluorescent labeling. By covalently conjugating Cy5.5 NHS ester to the surface of biomimetic nanoparticles, researchers achieved real-time, non-invasive monitoring of nanoplatform distribution and accumulation in neural tissues, critical for evaluating the safety and targeting of neuromodulatory devices. This application bridges molecular imaging with functional bioelectronics, underscoring Cy5.5’s versatility in both basic research and preclinical development.

Key Innovation from the Reference Study

The reference study introduces a transformative approach to non-invasive epilepsy treatment by harnessing ultrasound-triggered, biomimetic piezoelectric nanoplatforms. Instead of relying on surgically implanted electrodes for neuromodulation, these platforms use ultrasound to activate piezoelectric materials, generating localized electric fields that modulate neuronal activity. To track and validate these platforms in vivo, researchers employed near-infrared dyes for optical imaging—directly leveraging the deep-tissue penetration and low autofluorescence background of Cy5.5 NHS ester (non-sulfonated).

In practice, this means that when designing nanoparticle-based or polymer-based neuromodulation systems, the inclusion of a near-infrared fluorescent dye such as Cy5.5 NHS ester enables quantitative biodistribution studies, temporal tracking of therapeutic delivery, and non-invasive safety assessment—capabilities that are essential for translation into clinical research. This insight guides assay developers to prioritize dyes with high extinction coefficients, robust photostability, and proven performance in complex biological environments.

Troubleshooting and Optimization Tips

Despite its robust performance, optimizing Cy5.5 NHS ester (non-sulfonated) labeling requires attention to several critical factors:

• Buffer interference: Avoid using Tris, glycine, or other amine-containing buffers during conjugation. These can compete with your target biomolecule, dramatically reducing labeling efficiency.
• Hydrolysis risk: NHS esters are susceptible to hydrolysis in aqueous solutions, especially at higher pH. Prepare the dye stock immediately before use and minimize exposure to water prior to mixing with target molecules.
• Over-labeling: Excessive dye incorporation can quench fluorescence or impair biomolecule function. Empirically optimize the dye-to-protein ratio; typical ranges are 2–5 molar equivalents, but the optimal value varies by target size and structure.
• Aggregation and precipitation: If precipitation occurs during labeling, reduce dye concentration or increase organic co-solvent (up to 10% DMSO is generally well tolerated by most proteins).
• Storage: Store the solid dye at -20°C, protected from light. Do not store dye solutions long-term; use within a few hours of preparation for best results, as per the product page.

For further troubleshooting, protocol resources provide detailed flowcharts and decision trees to resolve low labeling efficiency or signal loss, while in vivo imaging guides offer advanced tips for maximizing detection in live animal models.

Comparative Advantages: Why Cy5.5 NHS Ester (Non-Sulfonated)?

Compared to other fluorescent dyes, Cy5.5 NHS ester (non-sulfonated) stands out for:

• Superior tissue penetration: Near-infrared emission reduces background autofluorescence and enables imaging at greater depths, outperforming most visible-spectrum dyes in in vivo applications.
• High labeling efficiency: With a high extinction coefficient and quantum yield, even low-abundance targets can be visualized with excellent clarity.
• Proven flexibility: From protein and oligonucleotide labeling to nanoparticle and polymer conjugation, Cy5.5 NHS ester adapts across workflow requirements, as highlighted in studies on tumor-microbiome imaging and polysaccharide bioactivity research.

For researchers seeking a trusted supplier, APExBIO offers validated, high-purity Cy5.5 NHS ester (non-sulfonated) with comprehensive technical support and batch-to-batch consistency.

Future Outlook: Enabling the Next Generation of Optical Imaging

The integration of Cy5.5 NHS ester (non-sulfonated) into advanced experimental systems—such as ultrasound-responsive piezo-nanoplatforms—signals a new era for non-invasive neuromodulation and deep-tissue optical imaging. The reference study demonstrates that combining precise molecular labeling with functional nanomaterials can overcome the traditional limitations of both pharmacotherapy and implant-based neuromodulation, offering safer and more effective therapeutic strategies for conditions like epilepsy.

Looking forward, the continued refinement of dye chemistries, conjugation workflows, and imaging modalities will further expand the capabilities of near-infrared fluorescence tools. Cy5.5 NHS ester (non-sulfonated) is poised to remain at the forefront of this evolution, enabling real-time, longitudinal tracking of biomolecules, cells, and nanoscale devices in increasingly complex biological systems.

For comprehensive product details and ordering information, visit the Cy5.5 NHS ester (non-sulfonated) product page.