As with any nanoparticle, the properties of silver nanoparticles are dependent on size. Many synthesis strategies produce nanoparticles with a wide size distribution. One way to separate these particles based on size is to use density gradient centrifugation. A sucrose gradient is an easy way to perform this separation because the sucrose gradient is simple to create using common laboratory equipment.
Proteins are fundamental building blocks for life. All tissues and organisms are made up of protein, and all of the work performed inside and outside of cells is mediated by protein signaling cascades. Proteins are polymers of amino acids with three or four layers of organized structure. Primary structure is defined as the linear order of amino acids. This is dictated by the genome: the code is transcribed from DNA and translated into the string of amino acids. Secondary structure is thought of as two basic forms: a beta sheet or alpha helix. The string of amino acids adopts the conformation that allows the lowest energy state. Beyond the sheets and helices, the chain can take other twists and turns to fold into a shape known as its tertiary structure. Some proteins are actually made up of two or more subunits of individually folded amino acids strands. The complexing of protein subunits to form one functional protein is called quaternary structure. All of this folding is extremely important to the character and function of each individual protein because it results in certain side chains of amino acids being located on the exterior or interior of the protein. Importantly, the folds create binding pockets where key amino acids are located to create a unique chemical landscape that allows the protein to bind to other proteins and carry out its job in a signaling cascade.
An in vitro diagnostic product (IVD) is any reagent, device, system, or part of a system used outside of the body to diagnose a disease or infection. The IVD can be used to detect DNA/RNA, microorganisms, or protein. This can be in a laboratory setting or in a “point of care setting.” Point of care (POC) is beneficial because it removes the need to send a sample to a laboratory for testing. Therefore, the time between sample collection and diagnosis is significantly reduced. Point of care IVD is especially useful in resource-poor settings where laboratories are located far away and there is a lack of good communication or transportation infrastructure.
Gold has always held a special allure for humans throughout history: wars were fought over it, alchemists strived to turn other metals into it, graves were looted for it, and love was sworn by it. Gold is so entwined in our lives that many people don’t even realize that it is fundamental to many state-of-the-art biotechnology. One of the most useful modern properties of gold is the creation of a surface plasmon resonance condition upon exposure to incident light of a resonance frequency. Gold used in this way is applied as a thin layer on a surface plasmon resonance (SPR) chip or is used as nanoparticles in Surface Enhanced Raman Scattering (SERS). These aqueous solutions of gold nanoparticles (5-50 nm in diameter) are the least recognizable form of gold because these colloidal solutions actually appear reddish in color rather than the characteristic yellow color of larger solid gold. It turns out that the work of the alchemists was not wasted. The discovery of aqua regia (noble or royal water) by an alchemist in the 8th century AD is critical to gold nanoparticle synthesis. This powerful mixture of nitric acid and hydrochloric acid is capable of dissolving solid gold to make chloroauric acid, which is the starting point for gold nanoparticle synthesis.
Cell separation is widely used in research and clinical therapy. For research purposes, sorting cells from a heterogeneous population enables the study of the different isolated types. From a therapeutic perspective, cell separation allows for the therapeutic infusion of enriched cell populations into a patient. Moreover, the latest advances in stem cell therapy, tissue engineering and regenerative medicine show the potential of cells derived from different tissues. The use of highly selective separation processes is critical to improve the quality of these cell-based treatments.
The sandwich ELISA is a type of Enzyme-linked immunosorbent Assay that uses two antibodies: a capture antibody and a detection antibody. The purpose of any ELISA is to detect the presence of a target antigen in a sample. In a sandwich ELISA the target antigen is bound between a capture antibody and a detection antibody. The capture antibody is immobilized on a surface, while the detection antibody (conjugated to an enzyme or fluorophore label) is applied as a last step before quantitation.
ELISA stands for Enzyme Linked Immunosorbent Assay. The immunoassay utilizes the specific lock-and-key recognition between antibodies and antigens. This recognition occurs naturally in the adaptive immune system; antibodies are created by the immune system when an antigen such as a virus or bacteria invades the body. The immune system recognizes the foreign invader and creates antibodies that specifically recognize surface proteins on the virus or bacteria. The antibodies are either attached to the surface of an immune cell or move freely through the body to tag the invader and begin a cascade of destruction and elimination. The most useful part of this process from a biotechnology and engineering perspective is the specificity of the antibody-antigen recognition.
Filtration is a simple technique used to separate solid particles from suspension in a liquid solution. There are many filtration methods available, but all are based on the same general principle: a heterogenous mixture is poured over a filter membrane. The filter membrane has pores of a particular size. Particles larger than the pores will be unable to pass through the membrane, while particles smaller than the pores will pass through unhindered. Additionally, all liquids will pass through. The final result of a filtration process is a collection of residue on the filtration membrane. This residue is therefore effectively separated from the rest of the mixture that passed through the membrane.
Fluorescent microspheres are small polymers embedded with fluorescent dye. They are a useful tool for medical imaging because they are non-toxic and non-biologically reactive when used as directed. Fluorescent microspheres are also useful in research laboratories as markers for fluorescent microscopy and as standards for flow cytometry fluorescent cell sorting. The main benefit of using a polymer microsphere embedded with fluorescent dye rather than using the dye alone, is two-fold: the matrix protects the dye from photobleaching, and the microsphere concentrates the dye leading to a more robust fluorescent signal.