Immunochemical methods immunoassays

The concept of immunoassay was first described in 1945 when Landsteiner suggested that antibodies could bind selectively to small molecules (haptens) when they were conjugated to a larger carrier molecule. This hapten-specific concept was explored by Yalow and Berson in the late 1950s, and resulted in an immunoassay that was applied to insulin monitoring in humans. This pioneering work set the stage for the rapid advancement of immunochemical methods for clinical use. 

Abstract A significant number of immunochemical methods have been described for the determination of the most important emerging pollutants. The present chapter is a compilation of the information available today regarding immunochemical determination of industrial residues with a high potential risk of causing negative effects in the environment, wildlife, and public health. Homogeneous immunoassays, ELISAs, FIIAs, immunosensors, and selective immunoaffinity sample treatment methods have been reported for the analysis of an important number of these substances. The bases of these methods are briefly presented. 

Several qualitative and quantitative immunochemical methods for CAP analysis in biological matrices of animal origin have been described [101,102, 104,105] (see Table 3). Van de Water et al. [ 102] described an ELISA that detected CAP in swine muscle tissue with an IC50 value of 3 ng mL1. This immunoassay was improved and subsequently optimized incorporating the streptavidin-biotin amplification system. There are also several commercially available test kits (see Table 4). RIDASCREEN is a competitive enzyme immunoassay for the quantitative analysis of CAP residues in milk, eggs, and meat in a microtiter plate. The measurement is made photometrically, obtaining a LOD of 100 ng L 1 in meat and eggs and 150 ng L 1 in milk. The test has been also applied to the analysis of tetracyclines. 

Immunochemical methods have been developed and placed on the market to analyze tetracycline residues (see Table 4). Thus, a qualitative EIA has been developed and used to analyze tetracyclines in honey samples with a detection level of 20 pg/kg-1 [96]. A microplate-based indirect ELISA has been developed to analyze tetracyclines using polyclonal antibodies. The assay could measure tetracycline in the range between 0.1 and 6 ng mL L Other tetracycline antibiotics such as chlortetracycline, rolitetracycline, or minocycline are also highly recognized in this assay [98]. Several immunoassay kits are commercially available for the analysis of tetracyclines although, to our knowledge, none of them... 

Benzodiazepines are an important group of drugs with tranquilizing properties. Available immunochemical methods include radioimmunoassays (164, 165), a radioreceptor assay (166), and nonseparation immunoassays such as the widely used enzyme-monitored immunotest (EMIT) and fluorescent polarization immunoassays (167, 168). Such assays generally require sophisticated apparatus and dedicated laboratories. However, a relatively simple enzyme-linked immunosorbent assay was recently described for screening benzodiazepines in urine (169). 

Immunochemical methods that utilize radioisotopic labeling can detect the use of anabolic sex hormones that increase the growth in meat animals. Stilbene [588-59-0], C14H12, trenbolone [10161-33-8], and zeranol [55331-29-8], C18H2605, can be successfully monitored by these immunoassay techniques (45). In order to prevent veterinary dmgs from being transported to the human food chain, radioisotopic immunoassays were developed to monitor veterinary antibiotics such as penicillin and chloramphenicol [56-75-7], C H CyX C, in meat, milk, and eggs (qv) (see Antibiotics Meat products Milk AND MILKPRODUCTS). 

The development of immunoassays for the detection of food components and contaminants has progressed rapidly in the last few years [7]. Antibodies against almost all the important food residues compounds are currently available. Classical immunochemical methods such as immunodiffusion and agglutination methods for food analyses generally involve no labeled antigen or antibody. Concentration of the antigen-antibody complex is estimated from the secondary reaction that leads to precipitation or agglutination. These methods are not sensitive, are subject to... 

Several qualitative and quantitative immunochemical methods and their application to the analysis of environmental samples have been described for OP insecticides, a family that includes widely used pesticides such as azinphos-ethyl/methyl, dichlorvos, fenitrothion or fenthion, malathion, mevinphos, and parathion. Mercader and Montoya202 produced monoclonal antibodies against azinphos-methyl and developed an ELISA that was used for the analysis of water samples from different sources, reaching detectability levels near 0.05 pg I. Watanabe et al.203 reported the production of polyclonal antibodies and ELISA procedures to analyze fenitrothion in river, tap, and mineral water (LOD = 0.3 pg L ). Banks et al.204 produced polyclonal antibodies against dichlorvos, an organophosphate insecticide used for stored grain, which also cross-reacts with fenitrothion. Nishi et al.205 reported the first immunoassay for malathion. Residues of this insecticide have... 

Wengatz, I. et al., Recent developments in immunoassays and related methods for the detection of xenobiotics, ACS Symposium Series 646 (Environmental Immunochemical Methods), American Chemical Society, Washington, D.C., 1996, pp. 110-126. 

The sensitivity of the overall analytical procedure depends upon many factors obviously including the type of sample to be analyzed and the skill of the analytical chemist. If an immunoassay is used to measure the amount of pesticide in a water sample by adding the water sample directly to the immunoassay, very high sensitivity may not be obtained although the assay will require very little time to perform. Alternatively, if the water sample is extracted and the immunoassay is employed only after several highly efficient cleanup steps, phenomenal sensitivity may be obtained at the expense of a large investment in time. In some situations, immunochemical methods may decrease the limit of detectability of a pesticide residue (77), but more importantly they may, in some cases, decrease the time and cost needed to reach a level of detectability as has been demonstrated with parathion (31). 

Already in progress is a second volume that will supplement the topics presently covered and include other important techniques. Innovative and practical applications of immunochemical methods have been described in other volumes of this series. We have avoided duplication so far as possible, and have included a cross-reference bibliography for each section (see pp. 481-484) to direct the reader to related papers in other volumes. Subsequent volumes will be involved with the development and application of immunoassays for specific compounds as well as for different classes of compounds. 

Despite the fact that immunoassays can be sensitive, specific and rapid, their application to detect compounds of environmental importance has been limited to relatively few laboratories (7-10). This symposium volume serves an important function since it focuses on the current status of the immunochemical methods being used for environmental analyses. Many of the accompanying papers consider the basic principles and essential steps in setting up immunoassays, i.e. the covalent linkage of small molecules to carrier proteins, immunization with these... 

---