Carboxyl Iron Oxide Nanoparticles (5–30 nm) – Catalog #B2026060

Carboxyl-functionalized iron oxide nanoparticles unite two powerful capabilities: a magnetic core for rapid separation and a reactive carboxyl surface for covalent coupling. These 5–30 nm particles are supplied as a stable liquid suspension, making them immediately useful for immunoprecipitation, affinity capture, and targeted purification. The small size ensures rapid sedimentation in a magnetic field and rapid kinetics of binding and release. The carboxyl groups enable direct coupling of antibodies, streptavidin, biotin, aptamers, and other targeting ligands via standard carbodiimide (EDC) or carbodiimide/sulfo-NHS chemistry.

Scientific Overview

Iron oxide nanoparticles, particularly magnetite (Fe₃O₄), possess superparamagnetic properties at sizes below ~100 nm. This means they develop strong magnetic moments in the presence of an external magnetic field but retain no residual magnetization when the field is removed. This property enables rapid, reversible capture and release of particle-bound targets, a hallmark advantage over permanent magnets or ferromagnetic particles that can aggregate.

The carboxyl surface coating provides reactive anchor points for covalent attachment of proteins, peptides, and other molecules. Carboxyl groups are activated via EDC (1-ethyl-3-(3-dimethylaminopropyl)carbodiimide) with or without sulfo-NHS to form reactive O-acylisourea intermediates that readily react with primary amines on proteins. This chemistry is mild, aqueous, and highly reproducible, making it the gold standard for biomolecule attachment to nanoparticles. The small particle size (5–30 nm) maximizes surface area per unit mass and minimizes steric hindrance, supporting high coupling densities and rapid binding kinetics.

Key applications include:

• Immunomagnetic separation: capture antibody-bound cells, pathogens, or proteins from complex mixtures
• Affinity purification: isolate His-tagged, biotin-tagged, or antigen-specific proteins without centrifugation tubes or columns
• Co-immunoprecipitation: pull down protein–protein complexes using magnetic beads coated with capture antibodies
• Biomarker enrichment: isolate rare cells, exosomes, or circulating tumor DNA before downstream analysis
• Drug conjugation research: attach small molecules or peptides to a magnetic scaffold for screening or targeted delivery

Usage & Handling Guidance

Before coupling, gently mix the suspension to resuspend any settled particles. For EDC coupling, dilute the nanoparticle suspension in coupling buffer (typically 10 mM MES, pH 4.5–6.5), add EDC and optionally sulfo-NHS, then add your target protein. Incubate 30 minutes to 2 hours at room temperature or 4 °C. Wash by magnetic separation (applying a magnet to the side of the tube) 2–3 times. Coupled particles are then ready for capture experiments or may be stored at 2–8 °C in PBS with a carrier protein (e.g., 0.1% BSA) to prevent aggregation.

• Use a strong permanent magnet (neodymium or samarium-cobalt) held to the outside of the tube for rapid sedimentation
• Do not expose to powerful electromagnets or strong static fields for extended periods, as this may cause irreversible aggregation
• Always include a protein carrier (BSA, casein) in long-term storage buffers to prevent non-specific aggregation
• Minimize freeze–thaw cycles; store coupled particles in glycerol or ethylene glycol-containing buffers if freezing is necessary
• For removal of excess EDC or coupling reagents, perform 3–5 magnetic washes in 1× PBS before use

What You Get

• 2 mL of carboxyl iron oxide nanoparticle suspension (5–30 nm, in aqueous medium)
• Particles ready to couple or use directly in magnetic separation workflows
• Storage buffer optimized for stability and minimal aggregation

Why Researchers Choose It

• Superparamagnetic behavior enables rapid, reversible capture without permanent aggregation
• Carboxyl groups allow quick, efficient protein coupling via standard EDC chemistry
• Small particle size (5–30 nm) ensures rapid equilibration and high surface-area-to-volume ratio
• Liquid suspension format requires no resuspension; ready to use directly in coupling or capture protocols
• Nanoparticle scale enables both bulk purification (mL scale) and high-sensitivity detection in analytical workflows

Frequently Asked Questions (FAQ)

• What is the typical coupling density?
  Coupling density depends on the target protein size, carboxyl group density, and incubation time. Literature reports 100–500 µg of protein per mL of carboxylated nanoparticles, equivalent to ~10⁸–10⁹ protein molecules per particle. Optimization for your protein is recommended.
• How do I prevent non-specific binding?
  Block the nanoparticles post-coupling with a carrier protein (1% BSA, 1% casein, or goat serum) and include detergents (0.01–0.1% Triton X-100 or Tween-20) in wash and incubation buffers. Pre-incubation of coupled particles in blocking buffer for 30 minutes before capture improves specificity.
• Can I couple antibodies, aptamers, or other molecules?
  Yes. Any molecule with a primary amine group (or convertible to one) can be coupled via EDC chemistry. Antibodies, streptavidin, biotin-conjugated ligands, peptides, and DNA aptamers are commonly used. Optimize EDC and target molecule concentrations for your specific application.
• How long do coupled nanoparticles remain stable?
  Properly stored coupled particles (2–8 °C, in PBS + 0.1% BSA) typically remain functional for 3–6 months. Storage in glycerol-based buffers can extend stability for longer-term use. Avoid repeated freeze–thaw cycles.
• Do I need a special magnet?
  A strong permanent neodymium magnet (e.g., 1–2 Tesla field strength) held to the outside of a standard microcentrifuge tube or well plate is sufficient for rapid sedimentation (30 seconds to 2 minutes). Electromagnets or weaker magnets may require longer incubation times.

References