Posted by The reason why nano-world or nano-technology attracts everyone’s attention is because when the material is in the nanometer size, it exhibits many physical and chemical properties that are different from macroscopic and molecular levels. For example, silver blocks can be electrically conductive. But when it is small enough to be nanoscale, it can’t conduct electricity. When copper is made of nanometer size, it becomes incapable of conducting heat. These new characteristics of nanomaterials have provided many new opportunities for people in the world of scientific research, and have quickly become the focus of the scientific and technological community. Magnetic nanoparticles are one of the many applications of nanotechnology in the biological field.
What are magnetic nanoparticles?
The so-called magnetic nanoparticles refer to small magnetic particles of a size suitable for measurement by nanometers, generally referred to as 1 to 100 nanometers. Such magnetic particles have a very special magnetic property called superparamagnetism, that is, it has strong magnetic responsiveness in the applied magnetic field, and after the magnetic field is removed, the magnetic properties of the magnetic particles disappear immediately, which means there is no remanence, and the particles are evenly dispersed in solution again. What scientists like is this feature, which can be used to adsorb a certain component in a solution and then magnetically separate the magnetic particles to achieve the purpose of separating the components. Of course, in order to be able to adsorb the desired substance, a specific group such as an amino group, a hydroxyl group, a carboxyl group or a thiol group must be coated on the surface of the particle, and by specifically binding these groups with the target molecule, and then collecting the magnetic particles by magnetic force, the desired substance can be separated.
The magnetic beads themselves are mostly inorganic materials, the most common material being magnetite, and the surface coating is basically organic. According to the positional relationship between the magnetic beads itself and the coating material, there are four kinds of structures for distinguishing the magnetic beads, namely, a core-shell type, a mosaic type, a shell-core type, and a shell-core-shell type.
Among them, the core-shell type is researched and used most, whose core is the magnetic material. The polymer material is encapsulated on the surface of the magnetic particles as a shell layer, contributing to the specificity of the entire particle, and the inorganic magnetic core imparts superparamagnetism to the whole particle, contributing to the availability for separation. In a well-mixed liquid environment, the polymer shell binds with the target substance through its functional group, and an external magnetic field controls the movement and collection of these particles, thereby finally achieving the purpose of separating the target substance. The tiny magnetic particles are so powerful that in addition to their superparamagnetism, they also possess the following characteristics:
1. It has good surface effect. The specific surface area increases sharply, the microsphere functional group density and selective adsorption capacity increase, the adsorption equilibrium time is greatly shortened, and the adsorption capacity is improved.
2. Physicochemical properties are stable, with a certain degree of biocompatibility, and will not cause significant damage to the organism.
3. Particle surface modification is available. The surface of the magnetic particle itself can be of or be modified to have functional groups (such as -OH, -COOH, -NH2, etc.), which can bind to biologically active substances (such as nucleic acids, enzymes, etc.), or can be coupled with specific molecules (such as specific ligands, antibodies, antigens, etc.) to specifically separate biological macromolecules.
The application of magnetic nanoparticles
1. Cell separation
Bioactive adsorbents or other ligands, such as antibodies and exogenous coagulations, are attached to the surface of the magnetic microspheres, and their specific binding to the target cells can be conveniently and quickly applied to separate the cells by the action of an external magnetic field. Magnetic microspheres also have important applications in the isolation, purification and detection of bacteria in microorganisms. The use of immunomagnetic microspheres combined with other immunoassay methods can quickly, accurately and efficiently separate microorganisms in samples, greatly improving the specificity of detection methods, and is of great significance for food hygiene and prevention of disease transmission. For example, the isolation of Staphylococcus aureus and Salmonella can be carried out without subsequent damage to the bacteria which can be further cultured.
2. Protein separation
Traditional protein separation methods such as salt precipitation, organic solvent precipitation, membrane chromatography and ion-exchange chromatography, generally achieve the purpose of separating proteins by changing the pH, dielectric constant, temperature or ionic strength of the solution. The operation process is cumbersome, energy-consuming, and the loss of the target protein is large. The magnetic microspheres have a small particle size, a large specific surface area, and a functional group on the surface, so that the coupling capacity is large, and it is capable of covalently binding a ligand which can be recognized and reversibly bound by the target protein. Then, the magnetic microspheres are added into the mixed solution containing the target protein, after the target protein is tightly bound to the magnetic microspheres, it is separated by an external magnetic field. The entire separation process does not require adjustment of the pH, temperature, ionic strength and dielectric constant of the mixed solution, thereby avoiding the loss of protein during the conventional separation process. Compared with traditional separation methods, protein magnetic separation technology has the advantages of being fast, high purity and high yield.
3. DNA extraction
Magnetic particles-based DNA extraction is widely used in various biological research. Because any DNA-related scientific research is inseparable from DNA extraction, and DNA extraction is the first step in all subsequent studies, so the efficiency of DNA extraction and the effect directly affects subsequent research. Magnetic particles-based DNA extraction has the following advantages:
1). The operation is simple, and the whole process is only four steps, that is, lysis, binding, separation and elution, without cumbersome centrifugation, most of which can be completed in 40 minutes;
2). High efficiency. The large surface area of the magnetic beads and the specific binding with the nucleic acid make the extracted nucleic acid high in purity and concentration;
3). It’s safe and non-toxic, and does not use any toxic reagents, such as phenol, in line with modern environmental protection concepts;
4). It can achieve automation, large-scale operation.
Traditional DNA separation techniques include precipitation and centrifugation. These purification methods are complicated, time-consuming, and low in yield, and are difficult to automate when exposed to toxic reagents. Magnetic particles-based separation technology can overcome these shortcomings well, and achieve rapid and efficient preparation of samples, which is an important direction for the development of future DNA purification methods.
Biomagnetic beads can also be used in gene chips, luminescence detection and disease treatment, and even as contrast agents, showing an extremely broad application prospect.