BioAssay Works FAQ, nanoparticle gold

A sol is defined as a colloid that has a continuous liquid phase in which a solid is suspended in a liquid. A colloid is a form of matter intermediate between a true solution and a mixture (suspension).

In a gold sol, gold particles so small they appear intensely red and remain suspended in water serve as the core component that enables rapid, point-of-care (POC) assays to detect minute traces of important substances. To accomplish this feat, nano-gold particles must be coated with appropriate receptors that react specifically with the molecules to be detected. BioAssay Works creates nanoparticle gold used in ultra-sensitive diagnostic tests. The Company's mission includes a service to assemble gold sols into working assay systems. BioAssay Works uses proprietary methods to create gold sols with a 10- to 15-fold increase in gold particle concentration over existing technology.

What size are the gold nanoparticles in a typical gold sol created by BioAssay Works? See the scanning electron microscopy image of gold particles coated on a latex bead in the image above. BioAssay Works produces gold sols in which gold particles are uniform in size (15, 20 or 50 nm, for example). Typical particles produced by conventional methods may range from 15-150 nm. "Red gold" particles are 15-50 nm, and are generally spherical. BioAssay Works creates wine-red gold sols.

How do gold sols relate to the Human Genome Project? One of the important spin-offs of the Human Genome Project is the identification of hundreds, if not thousands, of critical substances that need to be measured in the course of life-science research, and for the prevention of human, animal, and plant diseases. Some of these substances can be measured in the laboratory with sophisticated instrumentation, but many need to be measured rapidly at the point-of-care (POC).

What are rapid lateral-flow assays, and how are gold sols used in these tests? The behavior of a molecule as it reacts with ultra-specific receptors while it is being carried along a nitrocellulose membrane can be used to rapidly identify and measure the material. The critical agent for visualizing this reaction is gold particles that are so small (nanometers) that they appear red and remain suspended in water while they are transported along the nitro-cellulose. Ultra-sensitive tests based on this principle are often referred to as "rapid lateral-flow (immuno)assays." A common example of a rapid lateral-flow assay is the pregnancy test that measures the peptide hormone associated with pregnancy.

A good lateral-flow assay is very easy to perform and will provide an accurate answer within minutes. To achieve this performance, receptors bound to the gold particles must be carefully balanced with paired receptors striped on the nitro-cellulose membrane. Chemically, this process is the molecular equivalent of setting a mouse trap.

Stabilized gold conjugates made from concentrated sols are ready for use in lateral-flow and flow-through assays without additional optimizations. Typically, 5-15 µl gold conjugate per test will give optimally sensitive assays. The gold conjugate is excellent for use in a variety of gold-amplified assay procedures. This includes BioAssay Works' patented, ultra-sensitive C-FLAT technology. Researchers interested in evaluating this technology may contact BioAssay Works for a research-use license with no fee.

What are some of the technical problems associated with gold sols? The availability of lateral-flow assays continues to be severely restricted by the availability of reliable "gold conjugates," i.e., gold particles that have been coated with the appropriate receptors. Without going into too much technical detail, this availability problem stems from two issues: the chemistry involved in dressing the gold, and the problems associated with the scale-up of gold sols into reliable industrial products. A closely associated problem is the formulation of the eluant that carries the gold particles along the nitro-cellulose membrane in a manner that minimizes background noise and enhances the tell-tale gold reaction.

Storage, shipping, handling, and packaging can cause problems with current gold sols that are 1-OD concentrations. Stability over time becomes an issue. Gold loses its red color when partially reduced gold chloride comes out of the metallic lattice. A variety of reactions can cause this to happen. One possibility is that gold chloride continues to be reduced, such that gold-chloride becomes metallic gold plus HCl. A second possibility is that a metal chelating agent, (EDTA, for example), extracts the gold ions out of the gold lattice. Trace contaminants on the glass surface may possess reduction properties. Alternatively, the glass lattice may serve to chelate gold ions. Air itself may also be involved in the decomposition of gold. Macromolecules can suddenly lose activity as their concentration approaches zero. It seems this phenomenon is always in the background, which is one of the reasons that BioAssay Works' chemists work at concentrations that make this background reaction negligible.

How does BioAssay Works solve technological problems associated with gold sols?The founders of BioAssay Works have nearly 50 years of experience in the purification and development of bio-receptors in assay systems. Coupled with proprietary improvements that enable the synthesis of gold sols at concentrations 10-20 times conventional levels, BioAssay Works offers a powerful package of products and services that promise reliability and reduced costs for the development of rapid lateral-flow assays.

BioAssay Works' highly concentrated 15- to 50-OD Naked Gold® is produced by a proprietary process that does not involve the traditional boiling and centrifugation methods. This unique process allows the end-user to directly coat antibody or soluble proteins onto gold without the need to concentrate the gold via centrifugation. By eliminating the gold concentration centrifugation step, the potential for aggregates is greatly minimized. BioAssay Works' gold sols meet a high standard for lot-to-lot consistency.

BioAssay Works' services will help customers upgrade current ELISA assays to the rapid, lateral-flow format. BioAssay Works' products will provide customers with standardized Tell-Tale Gold® (gold-coated) ribbon and eluants used in these tests.

BioAssay Works supplies customers with Tell-Tale Gold® ribbon and assay solutions at prices substantially less than those offered by competing products. Test makers who create their own in-house reagents will benefit by switching to BioAssay Works as a supplier. In addition to cost savings for reagents, test builders will save through lowered quality-control costs.

Identity testing, explanation. Identity testing involves distinguishing one humanized monoclonal from another. In large pharma companies, it is not unusual to have multiple therapeutic humanized antibodies directed against cancer-cell epitopes, adhesion molecules, interleukins, cytokines and chemokines, hormones, etc. FDA mandates require in-house testing at all points of manufacturing (cell stock, cell growth, monoclonal expression, scale-up, bioreactor, purification, and vialing) to verify that the contents of a bottle are correctly identified. The most common method used for verification is anti-idiotypic antibody (reactive with only one type of monoclonal, usually in the variable active site region) coated on an ELISA plate, followed by humanized monoclonal capture and then amplification via an enzyme antibody reactive with the FC region on the monoclonal. A less common method is to coat the ELISA plate with the antigen with which the monoclonal reacts, and again use enzyme-anti FC as the amplifier after the monoclonal-addition step. The result is the same with either procedure: 100% certitude as to which monoclonal is which.

Rapid assays perform the same task as ELISA plates, with the added feature of multiplexing the tests, such that 3-4 monoclonals can be quickly identified in a single strip. Rapid assays require only 5-10 minutes. A second feature is ease-of-use; manufacturing personnel can test monoclonals with minimal training.

Rapid-identity assays allow pharma to follow the half-life of an injected monoclonal on prospective patients in a POC setting.

Residual-contaminant identification. An adjunct to identity testing is residual-contaminant identification and semi-quantitation. Rapid assays allow pharma to identify and follow the level of contaminating proteins at all production stages. FDA mandates an allowable level of residual proteins picked up during monoclonal production. The more common contaminating proteins are insulin, protein A, HSA, and transferrin. Different companies often have other unique contaminants such as growth hormones and interleukins. Rapid-assay products based on BioAssay Works' gold sols enable manufacturers to quickly and accurately identify residual contaminants. Rapid-assay technology provides the same result as ELISA-plate technology with less investment in time and training.

novel gold sol technology

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