Description

A high-performance conjugation technology is employed to fully functionalize the surface of magnetic beads with natural streptavidin. This design enhances the capture capacity for biotin-labeled molecules while reducing background signals. The streptavidin-bound magnetic beads exhibit superior functional stability and excellent uniformity on their surface.
The bead surface is coated with a layer of streptavidin featuring strong binding affinity, along with outstanding reproducibility. Additionally, the beads possess efficient liquid-phase reaction kinetics.

Specifications

Bead Size	500 nm
Coating Material	Polystyrene
Product Packaging	Available in various specifications: 1 mL, 5 mL, 20 mL
Solid Content	10 mg/mL

Binding Capacity

1 mg of streptavidin magnetic beads can bind to:

1200 pmoles of free biotin
500 pmoles of biotinylated oligonucleotides
20 μg of biotinylated antibodies

The binding capacity for double-stranded DNA depends on the length of the DNA fragments.

Principle

As a solid-phase matrix, streptavidin-conjugated magnetic beads can bind to various biotinylated complexes (such as small-molecule peptides, proteins, antibodies, carbohydrates, lectins, and oligonucleotide DNA/RNA) in a simple, rapid, and efficient manner. Therefore, they are applicable in fields including molecular and immuno-diagnostics, cell sorting, construction of cDNA expression libraries, and drug screening.

Precautions

The binding capacity of streptavidin magnetic beads is related to the size of the specific target molecule.
Ensure there is no excessive free biotin in the sample, as free biotin binds to streptavidin more easily than large-molecular-weight target molecules.
For PCR product solutions amplified with biotinylated primers, try to remove free biotinylated primers before binding to the magnetic beads — this is because biotin-labeled primers have higher binding affinity to magnetic beads than biotinylated DNA fragments. Free biotinylated primers can be removed via ultrafiltration, microdialysis, or general DNA purification and recovery methods.
It is recommended to optimize the dosage of magnetic beads through titration in each application. Both the size of the ligand molecule and the degree of biotinylation may affect their binding capacity. The ratio of magnetic beads to biotinylated ligands directly impacts the overall experimental results: with a constant amount of magnetic beads, when the concentration of biotinylated ligands is low, the target-binding capacity of the bead-ligand complex increases as the concentration of biotinylated ligands rises; however, once saturation adsorption is reached, further increasing the concentration of biotinylated ligands will not improve the target-binding capacity of the bead-ligand complex.
For the preparation of biotinylated ligands, biotinylation reagents produced by manufacturers such as Pierce or Sigma are recommended. Biotin labeling can be applied to various functional groups, including amines, thiols, carboxyl carbohydrates, tyrosine/histidine side chains, guanidines, and cytosine bases. Note that biotinylation may lead to the loss of target molecule activity, so precautions should be taken based on specific applications.
In DNA synthesis, biotin is generally labeled at the 5’-end of oligonucleotide primers. For protein biotinylation, reagents such as biotin-X-NHS Ester (from Pierce or Sigma) can be used.
After the magnetic beads bind to the ligand, when using the ligand to capture the target substance, ensure that the target substance is free in the solution and that its binding sites to the ligand are exposed.

Operational Procedures (For Reference)

A. Magnetic Bead Preparation

1. Before use, vortex the magnetic bead suspension thoroughly (ultrasonic dispersion can also be used: carefully place the test tube in a standard ultrasonic cleaner and sonicate for approximately 3 minutes). Use a pipette to transfer the required volume of magnetic beads into a centrifuge tube.

2. Place the centrifuge tube on a magnetic rack; separation is typically complete within approximately 1 minute. Use a pipette to remove the liquid.

3. Add the washing solution specified for the experiment, cap the test tube, and mix well by vortexing. Then, perform magnetic separation and remove the liquid.

4. Repeat the washing step 1–2 times, and resuspend the magnetic beads in an appropriate volume of solution.

- For antibody- or protein-related experiments: Wash the streptavidin (SA) magnetic beads 2–3 times with PBS or physiological saline buffer before use.
- For nucleic acid-related experiments: Wash the SA magnetic beads with 1× B&W Buffer at least 3 times before use.

Formulation of 2× B&W Buffer: 10 mM Tris-HCl (pH 7.5), 1 mM EDTA, 2 M NaCl.

This product does not contain ribonuclease (RNase). For RNA-related experiments, pre-treat the SA magnetic beads to remove RNase:

Wash the SA magnetic beads twice with Wash Buffer I (Wash Buffer I: DEPC-treated 0.1 M NaOH, DEPC-treated 0.05 M NaCl), 2 minutes per wash.
Then wash once with Wash Buffer II (DEPC-treated 0.1 M NaCl), and finally resuspend the SA magnetic beads in Wash Buffer II.

B. Binding to Biotinylated Ligands

1. Binding of Streptavidin Magnetic Beads to Biotin-Antibody or Biotin-Peptides

- Calculate the required amounts of magnetic beads and biotinylated antibody. Each mg of streptavidin magnetic beads can bind a maximum of 15 μg of antibody or 300 pmol of biotinylated peptide; saturation levels of antibody/peptide are generally not required.
- After resuspending the magnetic beads, incubate them with the biotinylated antibody at room temperature for 30 minutes, mixing by rotation.
- After incubation, place the centrifuge tube on a magnetic rack for 2 minutes and remove the supernatant.
- Wash the magnetic beads 4–5 times with PBS/BSA.
- Resuspend and dilute the magnetic beads to the desired concentration for downstream experiments.

2. Binding of Streptavidin Magnetic Beads to Nucleic Acids

- Take an appropriate amount of pre-washed magnetic beads.
- Resuspend the magnetic beads in 2× B&W Buffer to a final concentration of 1 μg/μL or a concentration suitable for the experiment.
- Add an equal volume of biotinylated DNA/RNA solution.
- At room temperature, mix by rotating or gently tapping the centrifuge tube. Incubate for approximately 10 minutes for ~30 bp fragments, and 15 minutes for ~1 kb fragments.
- After incubation, place the centrifuge tube on a magnetic rack for 1–2 minutes and remove the liquid.
- Wash the magnetic beads 2–3 times with 1× B&W Buffer.
- Finally, resuspend the magnetic beads in a solution suitable for downstream experiments and dilute to the desired concentration.

C. Dissociation of Streptavidin Magnetic Beads from Antibodies/Proteins and Nucleic Acids

1. Elution of Biotin-Labeled Antibodies/Proteins

Two elution protocols are provided below; select the appropriate method based on the requirements of subsequent detection.

a. Denaturing Elution (for SDS–PAGE Detection)

- Procedure: Add 50–100 μL of 1× SDS-PAGE Loading Buffer to the magnetic beads, mix well, and heat at 95°C for 5 minutes. Place on a magnetic rack to separate the magnetic beads, collect the supernatant, and perform SDS-PAGE detection.
- Note: If denaturing elution is selected, the eluate will contain streptavidin monomers, streptavidin multimers, and biotin-labeled antibodies/proteins.

b. Non-Denaturing Elution (for Preserving Biological Activity)

- This method maintains the native biological activity of the eluted sample, enabling subsequent functional analysis.
- Procedure: Add 50–100 μL of Elution Buffer II to the magnetic beads, and incubate at room temperature for 5–10 minutes. Place on a magnetic rack to separate the magnetic beads, collect the supernatant into a new EP tube, and immediately add neutralization buffer (0.1 M NaOH) at 1/10 of the total volume to adjust the pH of the eluate to neutral. The sample is then ready for subsequent functional analysis.
- Note: For non-denaturing elution, streptavidin may dissociate under acidic conditions—do not exceed 10 minutes of incubation. Acidic elution buffer disrupts most antibody-antigen interactions; for better elution efficiency, pre-wash the magnetic beads once with 1 mL of 0.1% Tween-20 aqueous solution.

Elution of Biotin-Labeled Nucleic Acids

Procedure: Add 50–100 μL of Elution Buffer (95% Formamide, 10 mM EDTA, pH 8.2) to the magnetic beads. Incubate at 65°C for 5 minutes or 90°C for 2 minutes. Place on a magnetic rack for magnetic separation, and collect the supernatant.

Documents

User Manual

Streptavidin Beads (500 nm)