Janus particles named after Roman god Janus who was illustrated with two faces, one looking to the future, and the other to the past. Pierre-Gilles de Gennes mentioned the term Janus particle in his Nobel lecture on soft matter in 1991. Janus particles are synthesized by joining two or more different materials together. Each material imparts a unique and useful quality to the particle; therefore, one Janus particle can display multiple properties and functionalities. It is this fundamental asymmetry that makes Janus particles a powerful tool in biotechnology for biosensing, bioseparation, self-assembly, drug delivery, and much more. This blog post will summarize a lengthy and informative reviewarticle of the same title that was published in Chemical Reviews in 2013.
Lluis M. Martínez, SEPMAG Chief Scientific Officer
Recent Posts
Janus Particles and anisotropy
Janus particles (JPs) have two or more properties or functions wrapped up into one package. There are many different synthesis methods, properties, and applications for JPs. Anisotropy is defined as an object having a different physical property or different value when measured in different directions. Janus particles are anisotropic. Their properties are asymmetric. They can have a hydrophobic face and a hydrophilic face. They can have magnetic properties as well as optical reporters on the same particle. JPs can have different optical properties on either side. They can have different ligands on opposing faces. It is anisotropy that makes them useful tools for biosensing and bioseparation. One particle with multiple functionalities is often more useful than an isotropic particle with one property.
The ability to isolate cells is important in both clinical and research settings. There are many available techniques for cell separation. These techniques differ in specificity of cell selection, cost of equipment, time to complete, technology needed, and skill required. Cell separation based on cell density is rapid and inexpensive, but is unspecific. Still, it is a fundamental technique that is commonly used in a variety of settings for general cell separation.
Antibodies labeled with fluorescent tags, radioactive molecules, biotin, enzymes, and other small molecules are essential for immunoassays, cell sorting, diagnostic assays, cell imaging, and other procedures. The attachment of small molecules to individual antibodies is not trivial, and to do it with a specific orientation is especially challenging. The purified antibody to be labeled must be in solution at high concentrations, and the process requires multiple washing steps. On-bead labeling methods are used to improve the labeling efficiency. Protein A binds to the Fc region of IgG antibodies across a variety of species, and is commonly used to capture antibodies onto a bead surface for isolation or for small molecule modification.
In this post we will cover in detail chemiluminescence definition and many chemiluminescence examples. The Chemiluminescence definition is the release of light from a chemical reaction. The light is released either from a high-energy intermediate itself or when a high-energy intermediate relaxes down to the lower energy final product. It is important to remember that chemiluminesence is the result of a chemical reaction, and is not the same as fluorescence. This means that chemiluminescent reactions do not need an input of excitation light of any kind. The overriding chemical formula of chemiluminescent reactions is
In-vitro diagnostic assays are used to diagnose infection or disease by specifically targeting a unique surface antigen or DNA sequence. Traditionally it was necessary to increase microbe density by culturing the sample for a few days under strict laboratory conditions. This was an important step toward obtaining enough genetic material for accurate analysis by qPCR.
Streptavidin magnetic beads are used to isolate biotinylated biomolecules
The affinity between streptavidin and biotin is one of the strongest non-covalent interactions known in nature. It is extremely specific and is unperturbed by extreme changes in temperature, pH, and detergent. It is therefore a very useful tool in biotechnology. For example, the system is commonly used in magnetic separation. Target molecules are biotinylated, which means that a biotin molecule is covalently attached to the protein, nucleic acid, or other molecule of interest. Streptavidin-bound magnetic particles are incubated with a solution containing the biotinylated target molecule for a sufficient time for the streptavidin-biotin affinity to form. The complexes can then be isolated from solution by magnetic separation.
The Zika virus (ZIKV) is emerging as a global public heath threat. It has been linked to the development of microcephaly in newborn babies whose mothers’ were infected by ZIKV during pregnancy. Recently, it has been shown that the virus can be sexually transmitted. The clinical signs in adults include fever, rash, joint pain, and conjunctivitis, which are common clinical signs for a general viral infection. This makes clinical diagnosis difficult without a specific immunoassay. The current methods for ZIKV detection are qPCR (quantitative polymerase chain reactions) or ELISA (enzyme-linked immunosorbent assay). Each of these is time consuming and the reagents can be expensive. As more people become infected and the virus spreads throughout the population it will become necessary to find a cheaper and faster alternative assay for detection of ZIKV. A magneto-actuated chemiluminescence immunoassay for the Zika virus has been developed. The demonstrated limit of detection is comparable to qPCR.
CD4+ lymphocytes are of particular interest in patients infected with Human Immunodeficiency Virus (HIV). A devastating effect of this retroviral infection is a progressive loss of CD4+ cells. These cells are crucial to a healthy immune system. When the level of CD4+ cells fall below 200cells/uL whole blood the patient is diagnosed with Aquired Immune Deficiency Syndrome (AIDS).
Therefore, the number of CD4+ cells in these patients is a good way to determine when to start antiretroviral treatment, and to administer drugs to protect against opportunistic pathogens. Currently, the most accepted way to measure the CD4+ concentration in whole blood is to use flow cytometry. However, this technology is extremely expensive and requires trained technicians to operate and maintain the machine. An alternative method is needed in resource poor areas. This alternative method would ideally be implemented at the point of care to avoid transportation of samples to and from a laboratory. One such recently developed technology is a magneto-ELISA to detect the concentration of CD4+ lymphocytes in whole blood. The detection system relies on magnetic separation to obtain an isolated population of CD4+ cells. It has a demonstrated limit of detection of 50 Cd4+ cells per μL, which is sensitive enough to diagnosis AIDS.
Efficient methods for DNA detectionin clinical, environmental, and experimental samples are constantly in demand. In a clinical sample, DNA capture and identification can be essential to the diagnosis of disease. In public heath and environmental situations it can be used to identify contamination of food or water. DNA collection and characterization is constantly expanding our ability to answer experimental questions. DNA capture is a mainstay of modern biotechnology. Traditional techniques rely on affinity columns, centrifugation, and multiple washing steps. Newer methods are based on magnetic separation. In the beginning, magnetic separation was limitedto packing a column with magnetic material and running a solution through it. As nanotechnology evolved it became possible to use mobile solid support systems such as magnetic nanoparticles.
