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 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.

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.