What are the properties of the immunomagnetic beads you use and how did they come about?
In the research and development of IVD reagents, immunomagnetism should be familiar to everyone. You should deal with it every day. It has the unique advantages of solid-phase reagents and the high specificity of immunological reactions, so it is widely used in immunoassays, immunoadsorption, and cell culture. It is increasingly widely used in fields such as isolation and culture. Magnetic microspheres are composed of carrier microspheres and ligands. Ideal magnetic microspheres are uniform spherical particles with superparamagnetic properties and protective shells. This article briefly introduces the performance, preparation and application of immunomagnetic beads in IVD.
1. Introduction to the properties of magnetic microspheres
1. Magnetic materials
γ-Fe2O4, Me-Fe2O4 (Me = Co, Mn, Ni), Fe3O4, Ni, Co, Fe, Fe-Co and Ni-Fe alloys, etc. The most studied and widely used one is iron and its oxides. (Fe, Fe2O4 and Fe3O4, etc.).
2. Polymer materials
Polyethylenimine, polyvinyl alcohol, polysaccharides (cellulose, agarose, dextran, chitosan, etc.) and bovine serum albumin, etc. The surface often carries chemical functional groups, such as -OH, -NH2, -COOH and -CONO2, etc., so that magnetic microcarriers can be coupled to almost any biologically active protein.
3. Functional ligand
The ligand must have biological specificity, and the combination of the carrier and the microsphere with the ligand will not affect or change the original biological properties of the ligand, ensuring the special recognition function of the microsphere.
Magnetic polymer microspheres determine the size and shape of immunomagnetic microspheres. Hirschein obtained the relationship between the external magnetic field force and the magnetic microspheres as:
F=（Xv-Xv0）VH（dH/dX）
Among them, F is the force of the external magnetic field; Xv is the magnetic susceptibility of the magnetic microspheres; Xv0 is the magnetic susceptibility of the medium; H is the external magnetic field; The force F exerted on a magnetic particle in a magnetic field is proportional to the size of the particle. When the particle diameter D>10μm, it can be separated under a weak magnetic field, is easy to precipitate, and has a small amount of adsorbed biomolecules; when the diameter D
F is also related to the magnetic susceptibility of the magnetic microspheres. The magnetic susceptibility of the microspheres is directly determined by the composition and size of the magnetic powder as the magnetic core. Commonly used oxide deficient materials become superparamagnetic materials when the crystals of their structures are less than 30nm. When the crystal is larger than 30nm, it becomes ferromagnetic. Large specific surface and high dispersion stability: As the microspheres become refined and their particle size reaches the nanometer level, their specific surface surges, the functional group density and selective adsorption capacity of the microsphere surface increase, and the time to reach adsorption equilibrium is greatly shortened. , the dispersion stability of the particles is also greatly improved.
4. Soft magnetic effect
Under the action of an external magnetic field, the soft magnetic polymer microspheres can generate magnetism and move directionally. The magnetism disappears after the magnetic field is removed, so that separation and magnetic guidance can be easily performed.
5. Biocompatibility
Nanomagnetic microspheres have good biocompatibility with most biopolymers such as polysaccharides and proteins. In bioengineering, especially in biomedical applications, good biocompatibility is very important.
6. Functional base characteristics
The functionalized groups on the surface of magnetic microspheres can be covalently linked to various active groups of biopolymers such as -OH, -COOH, and -NH2, and can stably immobilize biologically active substances (such as antibodies, antigens, receptors, etc.) on their surfaces. bodies, enzymes, nucleic acids and drugs, etc.).
Since nanomagnetic polymer microspheres have the above characteristics, they can be given a variety of specific reactive functional groups on their surface through copolymerization and surface modification according to different needs, and then combined with various functional substances. They are widely used in organic synthesis carriers, biophilic and chromatographic fillers, labeling and separation of cells, immobilized enzymes and bacteria, separation and purification of nucleic acids, biochip materials, industrial wastewater purification, carriers and immunoassays for targeted drug release systems, etc.
2. Preparation of immunomagnetic microspheres
1. Basic technical route
Microspheres of magnetic material are made, and then active groups are introduced on the surface of the microspheres. The antibody can be bound to the carrier through a carrier surface coupling reaction to form immunomagnetic microspheres.
2. Performance of high-quality microcarriers
Suitable and uniform magnetic response intensity, small and uniform particle size, stable, uniform and specific adsorption surface properties.
3. Preparation of magnetic microcarriers
(1) Embedding method
The magnetic particles are dispersed in the polymer solution, and magnetic polymer microspheres are obtained through atomization, flocculation, deposition, evaporation and other means.
(2) Monomer polymerization method
Core/shell magnetic polymer microspheres are polymerized by adding initiators, stabilizers, etc. in the presence of magnetic particles and monomers. Combination of antibody and magnetic carrier: The polymer layer on the surface of the magnetic microcarrier is activated and suspended in the antibody solution. The antibody can be connected to the surface of the microsphere by shaking it at room temperature or low temperature (ice water bath) for a period of time to obtain the immunomagnetic microcarrier. ball.
3. Application of immunomagnetic microspheres
1. Used for cell separation and purification
There are two ways to use IMB to separate cells; the method of directly separating target cells from the cell mixture is called positive separation; the method of using immunomagnetic beads to remove irrelevant cells and purifying the target cells is called negative separation. Immunomagnetic bead technology can be used to isolate various human cells such as red blood cells, peripheral blood eosinophils/basic granulocytes, neural stem cells, hematopoietic cells, T lymphocytes, γδT lymphocytes, human joint synovial cells, dendritic cells, and endothelial cells. cells, and various tumor cells, etc.
2. In vitro cell expansion
Cells such as dendritic cells (DC), hematopoietic stem cells, and progenitor cells have great application value in scientific research and clinical applications. However, they are relatively small in the body and widely distributed, making it difficult to obtain a large number of high-purity cells, which limits the use of these cells. development of the field. In vitro amplification supplemented by immunomagnetic bead technology is expected to solve this problem. In this process, immunomagnetic microspheres are used to separate and purify the cells to be expanded, and then culture them with a specific combination of factors. Many researchers use this method to find the best combination of cytokines for expansion and the best time for transplantation.
3. Immunoassay
Immunomagnetic microspheres can simply and quickly enrich and remove cancer cells from blood or bone marrow. They are widely used in disease detection, cancer treatment and autologous bone marrow transplantation. They are also used to non-invasively isolate fetal cells from maternal peripheral blood. Prenatal diagnosis.
Immunomagnetic bead separation technology is used in microbial detection to accurately and quickly detect Coli O 157 in samples, which is of great significance for food hygiene and preventing the spread of diseases. The combination of PCR technology and immunomagnetic bead technology plays a very important role in molecular biology, medical diagnostics, etc. The application of this research in medical detection can easily and quickly diagnose bladder cancer, breast cancer, prostate cancer, and peritoneal cancer. Gastric cancer, epithelial tumor cells, etc., making immunomagnetic separation technology more widely used.
4. Application in nucleic acid and genetic engineering
Immunomagnetic beads can be regarded as miniature ligands in affinity chromatography technology. With the help of the Biotin-Avidin system, immunomagnetic beads can bind to non-proteins. There is a high degree of interaction between biotin and avidin. With high affinity, the combination of the two is rapid, specific and stable, and their applications in the fields of molecular biology, medicine, immunohistochemistry and other fields are becoming more and more extensive. After combining with biomagnetic bead technology, it has produced attractive development prospects, and is widely used in the isolation and purification of RNA, mRNA, nucleic acid fragments, etc. and related research.
5. Used for tying
The immunomagnetic bead method can be applied to the rapid selection of clinical organ transplant donors and recipients. Under a high gradient magnetic field, the immunomagnetic bead method is used to isolate T and B lymphocytes from venous or peritoneal blood, and the isolated lymphocytes are used for HLA-Ⅰ class II antigen typing. For example, magnetic bead technology and monoclonal antibody reagents can be used to establish a new method that can complete HLA-I and II antigen typing in 1.5 hours. Immunomagnetic bead separation technology can also be used to conduct HLA typing of kidney transplant donors and recipients, and to explore blood Correlation between the therapeutic effect of repeated platelet transfusions and HLA in patients with the disease.
6. Used as a carrier for targeted drug release systems
As the carrier of the targeted drug release system, immunomagnetic microspheres can make the anti-cancer drugs on the immunomagnetic microspheres more accessible to cancer cells. After taking this preparation, use a magnet of appropriate strength at an appropriate location outside the body to remove the magnetic microspheres. Guided to specific target areas in the body, improving the effect of killing cancer cells. Many researchers have used different methods to prepare immunomagnetic microspheres targeting different cancer cells as carriers for targeted drug delivery systems, and have confirmed in experiments that this drug release carrier has good efficacy.
