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October 17th, 2007

The unexpected benefits of using magnetic nanoparticles in immunoassays

Abstract:
In old movies, saying "the rabbit died," was a popular way for a woman to reveal she was pregnant. The belief was that the doctor would inject the woman's urine into a rabbit. If the rabbit died, she was pregnant. The rabbit test actually originated with the discovery that the urine of a pregnant woman - which contains the hormone Human chorionic gonadotropin (hCG) - would cause corpora hemorrhagica in the ovaries of the rabbit. These swollen masses on the ovaries could only be detected by killing the rabbit in order to exam its ovaries. So, in reality, every rabbit died whether the woman was pregnant or not. Fortunately (for rabbits in particular), immunoassays - which can detect hormones (such as hCG), antibodies and antigens in the blood - were developed in the 1950s. Radioimmunoassays were first used to detect insulin in blood, but were later used for a variety of diagnostic tests. The technique is extremely sensitive and specific, but the necessary radioactive substances make it risky and expensive. In the 1960s, immunoassay technology was greatly enhanced by replacing radioisotopes with enzymes for color generation, which eliminated the risk and a great deal of expense. Today, most immunoassays are Enzyme-Linked ImmunoSorbent Assay, or ELISA. Because it can evaluate the presence of antigen or antibody in a sample, ELISA is commonly used to test for HIV, Hepatitis B, and West Nile Virus. ELISA has also been used in the food industry to detect potential food allergens such as milk, nuts, and eggs. Although there are numerous variations of ELISA, the test basically involves an antigen attached to a solid surface. When the antibody is washed over the surface, it will bind to the antigen. The antibody is then linked to an enzyme - usually a peroxidase (enzyme that causes oxidation) - which reacts with certain substrates, resulting in a change in color that serves a signal. The evolution of immunoassays has continued with developments such as fluorimetric immunoassay (which has replaced the rabbits in pregnancy tests.) Now, scientists at the Chinese Academy of Science have discovered a way to improve the process even more by eliminating one of the steps in certain immunoassays.

Source:
nanowerk.com

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