A reagent is an integral part of any chemical reaction. A reagent is a substance or compound that can facilitate a reaction, and they are used in the most commonly used tests. This includes, for example, pregnancy tests, blood glucose tests, and most COVID-19 test kits.

Reagents in chemistry

Reagents trigger chemical reactions. This term encompasses organic substances that trigger natural chain reactions in the body but also includes inorganic substances that can be used in artificially triggered reactions. Reagents are commonly used to test for the presence of certain substances, as the binding of the reagents to the substance or other related substances triggers certain reactions.

While sometimes used interchangeably with the term “reagent,” reagents and reagents are quite different. In a chemical reaction, a reactant binds to something and thus triggers a reaction. It is not consumed during this. However, a reactant is consumed. A reactant is a substrate in a reaction, while a reactant is a catalyst.

Rulers can also be limiting. Limiting reagents stop a chemical reaction when they are used up. The chemical reaction depends on the reactant to continue the reaction and stops when there is no more substance. Limiting reagents, therefore, dictate when a certain chemical reaction does not proceed.

The reagents are commonly used in laboratory settings for various tests. For example, Collins’ reagent is used to convert alcohols to aldehydes and ketones. As such, it can be useful for oxidizing acid-sensitive compounds. Fenton’s reagent, similarly, is used in the oxidation. However, Fenton’s reagent catalyzes the oxidation of contaminants in water and can be used to remove toxic compounds, such as tetrachlorethylene.

Reagents are often used to indicate the presence of compounds by causing changes in colours to indicate presence. For example, Fehling’s reagent can indicate whether carbohydrates or ketones are present and differentiate between the two functional groups. Millon’s reagent can be used to indicate the presence of proteins. The presence of protein, as inferred from the presence of tyrosine residues, causes the solution to which Millon’s reagent has been added to take on a reddish-brown colour.

Reagent kits and how they are used

Reagents, such as those listed above, are commonly used in laboratory or field settings to detect the presence of a variety of substances. For example, one of the widespread uses of reagents in everyday life is the detection of illegal drugs. While most kits, such as those used to test common drugs, are easy to use and involve noticing if there is a colour change, other kits are more complicated and require laboratory equipment such as chromatography.

Mandelin reagent kits are commonly used to detect alkaloids. This means that the kit can turn dark green if the drug amphetamine is present, and cocaine turns the color deep orange. Similarly, Marquis reagent kits can detect the drug LSD by turning olive-black when the drug is present in the solution. Marquis reagent kits can also test for methamphetamine and a variety of other drugs.

Reagents during COVID-19 testing

There are two main methods by which COVID-19 tests are performed: antibody tests and PCR-based tests. Both rely on reagents to successfully test for COVID-19 infections. In antibody tests, the compound that is detected in the reagent test kit is the antibody against the COVID-19 virus. In these cases, the patient’s blood is analyzed with enzymes as reagents. Test reagents bind to antibodies, such as IgG and IgM, and if they are present, a line will indicate this on the test kit. These tests are quick to perform and can indicate previous infection with the virus.

PCR, or polymerase chain reaction, tests whether the genetic material of the COVID-19 virus is present in the blood. Using real-time reverse transcription PCR (RT-PCR), the reagents used are enzymes to detect the specific genetic material, which is very unique to the virus. This is a more complicated form of the reagent test kit as it requires chromatography techniques. Lateral flow device (LFD) tests for COVID-19 have been developed later in the pandemic, to provide rapid, large-scale testing, for example in schools. detect antigens

However, as with other forms of reagents, those used to test for COVID-19 are limited and prone to problems in production and trade. Especially in a pandemic environment, this has become an issue, as previously laboratories and producers were operating at much lower capacity compared to the current need and a shortage of reagents on the same scale has never been encountered before. There are different reagents that are used to extract the virus or viral materials, others to amplify this, and then other reagents to test for its presence.

NATtrol Meningitis/Encephalitis

Quality Controls Of Infectious Diseases NATtrol

Globally, millions of people are screened for infectious diseases each year. The implications of reporting a false positive or false negative can be devastating to the patient. Accurate and sensitive diagnostics are needed to confirm that laboratories are providing patients with adequate test results. Consistent use of ZeptoMetrix® NATtrol™ controls helps monitor test performance and provides additional confidence in the quality and reliability of laboratory operations.

NATtrol™ (Nucleic Acid Assay Control) products are the industry’s preferred standard for molecular diagnostic testing and can be used as independent (third-party) quality control materials. NATtrol™ products are prepared from purified microorganisms that are grown in cell culture, microbial culture, or isolated from the plasma of infected individuals.

The NATtrol™ treatment modifies surface proteins and renders organisms non-infectious and stable in the refrigerator while preserving the entire genome. Inactivation of organisms is verified by the absence of growth invalidated tissue culture based infectivity assays or in validated growth protocols (as appropriate)

  • Non-infectious and stable in the refrigerator
  • Organisms purified and intact
  • Comprehensive process controls to monitor extraction and amplification steps
  • Available in different formats (single or multiple analytes)
  • Can be used in various molecular testing platforms and assays
  • Traceable to WHO international standards (where available)
  • 12-24 month shelf life
  • Extensive patent coverage* and/or patents pending

Frequent use NATtrol™ controls can be used to:

  • Train and monitor laboratory staff
  • Evaluate lot-to-lot consistency of test kits and assay reagents
  • Monitor daily variations in reported results
  • Provide an impartial and independent test proficiency assessment
  • Provide consistent, reliable and accurate quality control solutions
  • Help identify laboratory trends.

Polyclonal Antibodies

What are polyclonal antibodies (pAbs)?

Polyclonal antibodies (pAbs) are a complex mixture of various antibodies that are usually produced by different clones of B cells from an animal. These antibodies recognize and bind to many different epitopes on a single antigen and thus can form networks with the antigens.

How are polyclonal antibodies generated?

Antigen preparation

The quality and quantity of the antigen used directly affect the immune response. Even small amounts of impurities will cause the antibodies to react more to the impurity than to the desired antigen. Too little or too much antigen can cause sensitization, suppression, or other unwarranted immunomodulatory effects. Therefore, antigen purification is a crucial process to achieve higher antibody specificity.

The antigen must be prepared under sterile conditions to ensure that it is free from endotoxins. The amount of antigen depends on several factors, such as the properties of the particular antigen, the animal species chosen, the route of injection, the frequency of injection, and the level of purity of the antigen.

Selection of animal species

Factors that influence the choice of animal species are the amount of pAb required, the phylogenetic relationship between the animal and the antigen, the age of the animal, the ease of obtaining blood samples, and the application in which the pAb is used.

Animal species commonly used in the laboratory are rabbits, rats, mice, guinea pigs, hamsters, goats, chickens, and sheep. Rabbits are preferred due to their size and relatively long lifespan. However, to produce higher amounts of pAbs, farm animals such as goats, sheep, and horses are used.

Vaccination protocol

The immunization protocol differs for different animal species. Adjuvants are compounds that are used as a form of stimulation in cases where the induced immune response would otherwise be inadequate. The most widely used adjuvant for the production of pAbs is Freund’s complete adjuvant (FCA).

FCA induces high antibody titers against most types of antigens. However, care must be taken that FCA is not over-administered. FCA use should be limited to one-time use, as FCA can cause serious tissue damage. The smallest volume of an antigen capable of inducing an effective immune response is injected into the animal. However, the route of injection depends on the nature of the antigen and the animal used. The antigen can be injected as a single volume or several low volumes at different sites.

Booster injections are given if the antibody titer concentration has reached a plateau or is declining. Such injections do not always require an adjuvant, and very small amounts of the antigen are sufficient to enhance antibody concentration. A maximum of three booster injections is recommended.

Post-immunization observation

Animals are monitored daily for side effects of immunization and bled at regular intervals. Serum from animals is tested to monitor antibody responses and extract antibodies when a sufficient amount is produced.

Advantages of polyclonal antibodies

This is a relatively inexpensive process and can be used to isolate large quantities of an antibody in a single extraction. PAbs are a heterogeneous mixture of antibodies that can bind to a wide range of antigenic epitopes. Therefore, a small change in the epitopes of an antigen is less likely to affect pAbs. These antibodies are very stable over a wide range of salt concentrations and pH values.

Disadvantages of polyclonal antibodies

The affinity of pAbs for antigens can change over time, leading to a lot of lot-to-lot variabilities. Furthermore, the amount of pAbs produced is limited by the size and lifespan of the animal. The purity and concentration levels of a specific antibody are lower in pAbs than in monoclonal antibodies.

How are polyclonal antibodies used?

pAbs have a wide range of applications, including diagnostic tests and qualitative and quantitative biological analyses. For example, pAbs are used in immunofluorescence and immunohistochemical techniques such as sandwich ELISAs to detect tumour markers and other proteins of interest. pAbs are also used for mediating or modulating purposes, such as in immunotherapy, active signalling, or for neutralizing activities. An example of this is the use of pAbs in the treatment of Digoxin Immune Fab in fatal digoxin toxicity.

pAbs such as Rho (D) immunoglobulin are injected into mothers with negative Rhesus blood group to prevent hemolytic disease in a newborn. Rho (D) is produced from a pool of human plasma collected from Rhesus negative donors who have antibodies against the D antigen (present on red blood cells). pAbs also find applications in histopathological analyzes employing immunoperoxidase staining. In addition to these applications, pAbs are used in immunoaffinity purification for the purification or enrichment of antigens.

Recombinant pAbs are used in cancer therapy due to their ability to target multiple tumour cells compared to monoclonal antibodies. Although monoclonal antibodies are widely used in cancer therapy, relapse is common due to the appearance of tumour cells that are resistant to the antibody. By using pAbs, various recombinant antibodies can be developed that cross-react with different types of cancer.

The way forward shows the use of recombinant pAbs to minimize unnecessary polyreactivity as seen when using traditional pAbs. The use of pAbs in different assays not only leads to high throughput but can also be used to develop antibodies specific for human gene products that are also renewable.