What Are Magnetic Nanoparticles?

In February 2015, the x-ray research results of the German synchrotron showed that magnetic nanoparticles can improve the performance of high-polymer solar cells. This work was carried out by the Technical University of Munich, Germany. Polymer solar cells have low cost, but the conversion efficiency is only about 50% of silicon solar power. Therefore, many scientists are constantly working to improve the conversion efficiency of polymer solar cells. The work of the Technical University of Munich found that adding magnetic Fe3O4 nanoparticles to high-polymer solar cells can increase the cell conversion efficiency to 11%. However, it is advisable that the added amount does not affect its structure change.

Magnetic nanoparticles

In February 2015, X-ray research results from Deutsches Elektron-Synchrotron showed that magnetic nanoparticles can increase the performance of polymer solar cells. This work was led by Professor Peter Muller-Buschbaum of the Tecnical University of Munich (Tech: Germany: Technologie Universität München, TU München).

Polymer or organic solar cells have many advantages: cheap, flexible, and multiple properties; the disadvantage is that they are less efficient than silicon solar cells. Typical high-polymer solar cells convert solar energy to a few percent. But because it is cheap, it can still be used in some cases, and scientists are looking for ways to improve its conversion efficiency.

One feasible method is to add nanoparticles; for example, gold-added nanoparticles absorb additional sunlight and generate more charge carriers, which improves the conversion efficiency.

Muller-Buschbaum's research group uses a different approach; they believe that in solar cells, positive and negative charge pairs of charge carriers are generated. They need to be separated before positive and negative charge carriers are recombined, and then they are separated. The electrode flows in the opposite direction.

Electron spins can be divided into +1/2 and -1/2; the two electrons can be combined into 1 or 0 spins. Researchers are looking for ways to change the state of two electrons from zero to one: this requires nanoparticles of heavy elements; Fe3O4 is applicable in this case. In their experiments, adding Fe3O4 to polymer solar cells increased the cell's efficiency to 11%.

X-ray research results show that if too many nanoparticles are mixed in the solar cell material, its structure will change; if it is added at 1% by weight, its structure will not change. But the effect of adding 0.6% by weight of nanoparticles is the best; it can increase the efficiency of solar cells from 3.06 to 3.37%. This is good for a particular use.

Researchers also believe that for other polymers, adding nanoparticles can also increase their efficiency. But they believe that using X-rays alone as a research tool does not yet understand the specific mechanism why adding nanoparticles to polymers will increase the efficiency of solar cells.

Magnetic Nanoparticles / Magnetic Nanoparticles (MNPs) are new materials that have developed rapidly and have great application value in recent years. They are used in many fields of modern science such as biomedicine, magnetic fluids, catalysis, nuclear magnetic resonance imaging, data storage and Environmental protection has been used more and more widely. ^[1]

Magnetic nanoparticles have a series of unique and superior physical and chemical properties. With the development of synthetic technology, a series of magnetic nanoparticles with controllable shape, good stability and monodispersity have been successfully produced.
The magnetic properties of magnetic nanoparticles make it easy to perform enrichment and separation, or to perform directional movement and positioning. The magnetic effect is formed by the movement of particles with mass and charge. These particles include electrons, protons, positively and negatively charged ions, and so on. The charged particles rotate to produce magnetic dipoles, or magnetons. Magnetic domains refer to the arrangement of all magnetons in a volume of ferromagnetic material in the same direction under the action of an exchange force. This concept distinguishes ferromagnetic from paramagnetic.
Ferromagnetic materials have spontaneous magnetization and are magnetic when no external magnetic field is applied. The magnetic domain structure of ferromagnetic materials determines the dependence of magnetic behavior on size. When the volume of a ferromagnetic material is below a certain threshold, it becomes a single magnetic domain. This critical value is related to the intrinsic properties of the material, which is generally around tens of nanometers. The magnetic properties of extremely small particles originate from the size effect based on the magnetic domain structure of ferromagnetic materials. The assumption of this conclusion is that in the state with the lowest free energy, the ferromagnetic particles have uniform magnetic properties for particles smaller than a certain critical value, and non-uniform magnetic properties for larger particles. The smaller particles of the former are called single magnetic domain particles, and the larger particles of the latter are called multi magnetic domain particles.
When the diameter of a single magnetic domain particle decreases further than the critical value and the coercive force becomes zero, such particles become superparamagnetic. Superparamagnetism is caused by thermal effects. Superparamagnetic nanoparticles are magnetic under the action of an external magnetic field, but not magnetic after the external magnetic field is removed. In a living body, superparamagnetic particles are magnetic only when an external magnetic field is applied, which makes them uniquely advantageous in the living body environment. Crystal materials such as iron, cobalt, and nickel all have ferromagnetism, but because iron oxide magnets (Fe3O4) are the most magnetic among natural minerals on the earth and have high biological safety (materials such as cobalt and nickel are biotoxic), In many biomedical applications, superparamagnetic iron oxide magnetic nanoparticles are the most common.
Ferrofluids (ferrofluids) are liquids that become highly magnetic under the action of an external magnetic field. It is a new type of functional material that is both magnetic and fluid. A ferrofluid is a colloidal solution composed of nano-scale ferromagnetic or ferrimagnetic particles. The particles are suspended in a carrier solution. The carrier solution is usually an organic solvent or water. The nanoparticles are completely encapsulated by the surfactant to prevent aggregation into agglomerates. Ferrofluids usually do not remain magnetic in the absence of an external magnetic field and are classified as superparamagnetic. Nanoparticles in ferrofluids do not settle under normal conditions due to thermal motion.
The specific surface area (ratio of surface area to volume) of magnetic nanoparticles of spherical particles is inversely proportional to the diameter. For particles smaller than 0.1um in diameter, the percentage of surface atoms increases sharply, and the surface effect is significant at this time. The particle diameter decreases, the specific surface area increases significantly, and the number of surface atoms rapidly increases. When the particle size is 1 nm, the number of surface atoms is 99% of the total number of complete grain atoms. At this time, almost all atoms constituting the nanoparticles are distributed on the surface, and many dangling bonds are formed around the surface atoms. Other atoms combine to form a stable structure and show high chemical activity. Therefore, the efficiency of fixing the target molecule / atom is high.
Magnetic nanoparticles have good biocompatibility with many polymers. Surface modification of magnetic nanoparticles includes non-polymer organic fixation, polymer organic fixation, inorganic molecular fixation, targeted matching modification, and the like. Commonly used as modified substances are polyethylene glycol, dextran, polyvinylpyrrolidone, fatty acids, polyvinyl alcohol, peptides, gelatin, chitosan, methylsilane, liposomes, etc. There are two main ways to modify the surface of magnetic nanoparticles: first, the surface modification material and the particle surface rely on chemical bonds, which usually refers to some organic small molecular compounds; second, the organic nanoparticles are directly wrapped magnetic nanoparticles, mainly including the surface Active agents, polymers, precious metals and silica. Surface modification not only enhances the stability of magnetic nanoparticles, but also improves their dispersibility and biocompatibility in aqueous solution, improves targeting, prevents protein adsorption, increases their time in the blood circulation, and further compound other Nano-particles, compounds or biological ligands to achieve the functionalization of magnetic nanoparticles.

The application of magnetic nanoparticles in biomedicine is mainly divided into two categories: in vitro applications mainly include separation and purification, magnetic transfection, immunoassay, catalysis, Magnetorelaxometry, and solid-phase extraction. In vivo applications can be broadly divided into two categories: treatment and diagnosis. Therapeutic applications such as hyperthermia and targeted medicine, and diagnostic applications such as nuclear magnetic resonance imaging (NuclearMagentic Resonance, NMR).

Biological separation and purification is one of the most important technologies in biological and medical technology. This is also one of the most fruitful applications in magnetic particle applications. The magnetic separation method has the advantages of being efficient, simple and fast. Magnetic particles can be used for the separation of proteins, nucleic acids and other biomolecules and cells. The separation and purification of nucleic acids are made of nano-scale magnetic particles.
In biological separation, magnetic nanoparticles have small volume, large surface area, good dispersibility, and can quickly and effectively bind biomolecules. This binding is reversible, and floc formation can be controlled. Therefore, magnetic nanoparticles are used for separation. Better than traditional methods using micron resins and beads. Most magnetic nanoparticles used for separation are superparamagnetic-in the absence of an external magnetic field, the particles are non-magnetic and evenly suspended in the solution, and when an external magnetic field is used, the particles are magnetic and can be magnetically separated. Active substances such as biologically active adsorbents or other ligands attached to the surface of magnetic nanoparticles can specifically bind to specific biomolecules or cells and be separated under the action of an external magnetic field. The magnetic separation method basically includes only two steps: 1. labeling the target molecule or cell with magnetic nanoparticles; 2. separating the target molecule or cell by a magnetic separation device. One example of the use of magnetic nanoparticle separation is the binding of specific antibodies to magnetic nanoparticles, which can connect magnetic nanoparticles to specific cells, and externally apply a magnetic field to quickly separate magnetic nanoparticle-bound cells or perform immunological analysis. This method has high specificity, rapid separation and good reproducibility. For another example, glucose-DEAE is wrapped on the surface of magnetic nanoparticles, and the plasmid is purified from the bacterial lysate supernatant by ion exchange using the charge adsorption between the positively-charged DEAE and the negatively-charged nucleic acid.

It is a method for transfecting magnetic nanoparticles with carrier DNA into cells under the influence of external magnetic fields. The magnetic particles used for magnetic transfection are mostly surface modified with polycations and polyaziridines. Because they are positively charged, they are easy to bind to negatively charged DNA, and transfection efficiency is improved by tens to thousands of times compared to transfection with viral or non-viral vectors. Magnetic transfection also has the advantages of improved transgene expression, the use of extremely low-dose vectors can achieve both high transfection rates and high transgene expression, and simple methods of use. The magnetic transfection method has been successfully used for many types of adherent cells and a small number of suspension cells, including primary cells, tumor cells, and the like that are difficult to transfect with conventional methods. MagnetofectionTM magnetic transfection reagent produced by German Chemicell company has been selected by many of the world's top laboratories, and many articles have been published.
Immunoassay is an important method in modern biological analysis technology. It can be used to quantitatively analyze proteins, antigens, antibodies and cells. For example, in immunoassay, antibodies (or antigens) are often labeled with labels with special physicochemical properties such as radioisotopes, enzymes, colloidal gold, and organic fluorescent dye molecules. After the antigens and antibodies are recognized, The qualitative or quantitative detection of the marker achieves the purpose of detecting the antigen (or antibody). Due to the superparamagnetism of magnetic nanoparticles, it provides great convenience for the separation, enrichment and purification of samples, and has received widespread attention in immunoassay.
In recent years, the use of magnetic nanoparticles to support catalysts has been widely used to improve the problem of catalytic heterogeneity. Magnetic separation makes it easier to recover the catalyst in a liquid phase reaction than by cross-flow filtration and centrifugation, especially when the catalyst is in the submicron range. Such a small and magnetically separable catalyst has the advantages of high dispersibility, reactivity, and easy separation. In terms of recycling expensive catalysts or ligands, immobilizing these active materials with magnetic nanoparticles makes it easy to separate catalysts in quasi-homogeneous systems. In recent years, there have been transplanted catalytic sites onto magnetic nanoparticles for different types of transition metal-catalyzed reactions including carbon-carbon cross-linking reactions, olefin aldolization reactions, hydrogenation, and polymerization reactions. Catalysts that have been reported to support magnetic nanoparticles include enzymes, amino acids that hydrolyze esters, and organic amine catalysts that promote Knoevenagel and related reactions.

Net magnetic moment of the magnetic nanoparticle system after removing the magnetic field. There are two different relaxation mechanisms: Neil relaxation and Brown relaxation. The difference between these two mechanisms is the different relaxation time. In addition, Brownian relaxation occurs only in liquids, but Neil relaxation does not depend on the dispersibility of the nanoparticles.
Magnetorelaxometry is determined by the size of the nucleus, its hydrated diameter, and anisotropy. This technique can be used to distinguish between free and bound states based on the magnetic behavior of free and bound conjugates. Therefore, this technique can be used to evaluate immunoassays analyzing tool.
Magnetorelaxometry was originally used to evaluate immunoassays, and it can be used for in vitro or in vivo research. Magnetorelaxometry can quantitatively analyze the distribution of magnetic nanoparticles in organs or whole animals. Because this method is non-invasive, it can monitor animals for a long time, such as monitoring magnetically labeled stem cells. Another example is cancer diagnosis. Magnetic Relaxation Immunoassay (MARIA) using functionalized magnetic nanoparticles that has appeared in recent years is based on this physical method. The advantages of magnetic relaxation immunoassay technology are: the combined particles and free particles produce different signals, unlike traditional methods, no washing step is required; no labeling is required; each detection time is extremely short, so it can be used for high throughput Experiments; Because magnetic relaxation can be detected in opaque media, it can also be used for in vivo experiments; magnetic nanoparticles are combined with a technology based on the detection of magnetic relaxation using a highly sensitive magnetic field sensor such as SQUID (SuperconductiveQuantum Interference Device), Achieving high sensitivity. In this application, similar to separation and purification, nano-scale particles are better than micro-scale particles.
At present, Solid-Phase Extraction (SPE) has attracted much attention as a target component for separation and preconcentration from samples. Solid phase extraction is a common method for detecting trace contaminants from environmental samples. Recently, the application of nano-scale particles in sample extraction has been rapidly and greatly developed. Compared with traditional sample enrichment methods (such as liquid phase extraction), solid phase extraction is a good alternative. When separating and pre-concentrating target components from large volume samples, solid phase extraction methods using standard purification columns are time consuming. Therefore, Magnetic Solid-Phase Extractin (MSPE) using magnetic or magnetizable adsorbents becomes more important. In this process, a magnetic adsorbent is added to a solution or suspension containing a target component. Then, using a suitable magnetic separation device, the magnetic adsorbent having adsorbed the target component is recovered.
In the environmental sciences, research on the removal of organic and inorganic pollutants with magnetic nanoparticles has been conducted in recent years, and experiments using them to remove pollutants from groundwater, soil, and air have been used in laboratories and on the field scale. High concentrations of organic pollutants are mostly dyes. Wastewater from weaving and dyeing factories, pigment factories, and tannery factories contains dyes. Substituting magnetic nanoparticles for expensive or inefficient adsorbents can be a good platform, but more research is still needed. A major aspect of removing inorganic contaminants is the removal of metal toxins. Magnetic nanoparticles, as sorbents for removing metal toxins from complex matrices, have the advantages of high capacity and high efficiency. Due to their small size and large surface area, they are better than micron-sized sorbents. These findings will help design better adsorption treatment plans to remove or recover metal ions from wastewater. In addition, functional magnetic nanoparticles can be used to isolate and detect microorganisms such as bacteria and fungi in environmental samples.

Two main properties that affect magnetic nanoparticles for in vivo applications are size and surface function. The diameter of superparamagnetic iron oxide nanoparticles (SPIOs) has a great impact on their biological distribution in the body. Particles with a diameter of 10-40nm include ultra-small superparamagnetic iron oxide nanoparticles that can stay in the blood circulation for a long time. They can pass through the capillary wall and are often engulfed by macrophages that go to the lymph nodes and bone marrow.
Hyperthermia refers to placing superparamagnetic iron oxide in an alternating electromagnetic field, which can randomly change the magnetic direction between parallel and antiparallel, so that the magnetic energy is transferred to the particles in the form of heat. This property can be used to destroy sick cells in the body. . Tumor cells are more sensitive to temperature than healthy cells. Studies have shown that magnetic cationic liposome nanoparticles and dextran-encapsulated magnets effectively increase the temperature of tumor cells during thermal radiation therapy of cells. This method is considered to be the main method of cancer treatment in the future. The advantage of magnetic thermotherapy is that the temperature increase is limited to the tumor area. In addition, subdomain magnetic particles (nanoscale) are better than multidomain magnetic particles (micron) because they can absorb more energy in the AC electromagnetic field that the body can withstand, which is determined by their size and shape. Therefore, a clear and uniform synthesis path for producing particles is critical for strict temperature control.
Drug targeting has become one of the modern drug delivery technologies. Magnetic nanoparticles and an external magnetic field and / or a magnetizable implant can deliver the particles to the target area and fix the particles at a local site when the drug is released, so the drug can be released locally. This process is called Magnetic Drug Targeting (MDT). Recently, the use of iron oxide magnetic nanoparticles for targeted drug delivery has become increasingly feasible. Fe3O4 magnetic nanoparticles used in the core have a small diameter, high sensitivity, low toxicity, stable performance, and easy access to raw materials. Fe3O4 generally does not cause toxic side effects to the human body. The carrier used in the entire course of treatment does not exceed the conventional total iron supplementation for anemia patients. Except for part of the body's use, the remaining magnetic particles can be safely excreted through the skin, bile, kidney, etc. . Organic polymers or inorganic metals or oxides modified on the surface of the nanoparticles make them biocompatible and suitable for linking biologically active molecules to be functional. Delivering the drug to a specific site eliminates the side effects of the drug and reduces the dosage.
The application of magnetic nanoparticles in in vivo diagnosis is mainly used in nuclear magnetic resonance imaging. Due to the development of magnetic resonance imaging in diagnosis, a new class of drugs, magnetic drugs, has emerged. The main use of these drugs after administration to patients is to increase the contrast (contrast agent) of normal and diseased tissue and / or to display organ function or blood flow. Superparamagnetic iron oxide nanoparticles have become a new class of probes for cell and molecular imaging in vitro and in vivo. The use of superparamagnetic developers in nuclear magnetic resonance has the advantage of producing stronger proton relaxations than paramagnetic developers. Therefore, a smaller amount of developer needs to be injected into the body. However, MRI is not convenient for in situ monitoring.
Magnetic nanoparticles have shown unique advantages in the field of biomedicine, and their application in this field is still growing rapidly. Magnetic nanoparticles will play a greater role in the field of biomedicine and other fields.
German Chemicell company produces a variety of magnetic nanoparticles, magnetic nanoparticles, fluorescent nanoparticles, fluorescent particles, etc., suitable for a variety of biomedical applications. Beijing Qiwei Yicheng Technology Co., Ltd. represents all products of Chemicell. Some of Chemicell's magnetic nanoparticle products and applications are shown in the table below.

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