Immunoassays, literature

The development of sensitive and inexpensive immunoassays for low molecular weight pesticides has been an important trend in environmental and analytical sciences during the past two decades. 0.27-29 jq design an immunoassay for a pesticide, one can rely on the immunoassay literature for agrochemicals, " but many of the innovations in clinical immunoanalysis are also directly applicable to environmental analysis. - Conversely, the exquisite sensitivity required and difficult matrices present for many environmental immunoassay applications have forced the development of technologies that are also useful in clinical immunoassay applications. In the following discussion we will describe widely accepted procedures for the development of pesticide immunoassays. 

To understand how immunoassay-based analytical methods can be constructed to comply with tolerance enforcement requirements, a brief examination of those requirements is in order. This discussion is not intended to be comprehensive but to highlight aspects of special significance to immunoassay method development. The reader is urged to consult the literature " for further details. 

The versatility of luminescence goes beyond intensity-, wavelength- and kinetic-based measurements. Fluorescence polarization (or anisotropy) is an additional parameter still largely unexplored for optical sensing yet widely used in Biochemistry to study the interaction of proteins, the microfluidity of cell membranes and in fluorescence immunoassays. Although only a few optosensors based on luminescence polarization measurements can be found in the literature, elegant devices have recently been reported to measure chemical parameters such as pFI or O2 even with the bare eye41. 

In the past, general chapters and reviews have been published, related to the characteristics of CL as analytical technique [7-9], mainly in the liquid phase [10-14], and its use as detection mode in flowing streams and immunoassay [15-17]. Two extensive reviews reported on the specific application of CL reactions according to the nature of the analyte (inorganic species, enzymes and nucleotides, acids and amines, carbohydrates, steroids, polycyclic aromatic compounds, and drugs) and covering the literature from 1983 to 1991 [18] and from 1991 to mid-1995 [19]. 

Immunoaffinity procedures can be performed either on-line or off-line, and can be coupled to chromatographic systems [ 118,119] or even to immunoassays [120]. Many examples can be found in the literature regarding the use of immunoaffinity extraction of drugs and pharmaceuticals from biological matrices, as well as of organic pollutants such as pesticides from environmental samples [115,121-124]. 

We start with examples of the sequential approach. With this approach, you begin with more routine experiments, ones that are reasonably likely to succeed (e.g., calibration or optimization procedures). The initial set of experiments can also serve as a test case and/or show that you can reproduce literature values. For example, Aga (P6) proposes first to explore conditions that will optimize immunoassay sensitivity, and Spain (P7) proposes to begin with a study of topography, using published methods and a self-assembled monolayer with a known structure. 

Enzyme-linked immunosorbent assay is a heterogenous immunoassay. Reactions involve a solid phase to which components are sequentially presented and successively bound. This method is very effective in the determination of the total alkaloid content. The positive characteristics of this method are the use of non-toxic reagents and basic equipment with low costs, a small sample volume and the ability to measure alkaloids in crude sample extracts. According to the literature, compared with results obtained from GLC, the precision of ELISA for quinolizidine alkaloids is not as high as that of the gas chromatography procedure, but is adequate for plant breeding purposes. The use of enzymes in developing the methods of quinolizidine alkaloids analysis looks likely to increase in the future. 

The association rate constants (k2) for solution-phase antibody systems are on the order of 107-108 M 1 s 1 [23] but those for reactions on synthetic solid phases and cell surfaces are two to four orders of magnitude slower, mainly as a consequence of the sluggish diffusion and slower mass transfer of the reactants to the interaction sites. The dissociation rate constant for heterogeneous systems (k j is on the order of 10 -10 5 s up to two orders of magnitude slower than for solution-phase systems, and for solid phase immunoassays, it is attributed to multivalent interactions and to surface coagulation or aggregation via translational diffusion in the presence of extensive cross-linking at the interface [23]. Most of the MIA-based assays described in the literature require equilibration times on the order of hours, and more synthetic efforts are required to reduce this analysis time. 

Since none of the liposomal immunoassay approaches described in the scientific literature thus far took advantage of surface immobilization techniques, one could envision a double-amplification biosensor in which surface modification plays an important role [35]. For example, consider a dehydrogenase enzyme marker system which requires an electroactive cofactor such as NAD+. In the enzymatic reaction scheme ... 

Ohmicron Corporation, Rapid Assay, literature on the environmental immunoassay, Ohmicron, Newtown, PA, 1994. 

Since the introduction of radioimmunoassay (RIA) by Yalow and Berson in 1959 (2), numerous books and review articles have been written on immunoassays. The reader is referred to the literature for a selection of reviews on general immunoassay methodology (3), RIA (4-7), theory [8] and statistical analysis (9,10), synthesis of immunogens (5,6,11,12), enzyme immunoassays (13,14), fluorescence immunoassay techniques (15), miscellaneous labels (16) and separation techniques (17), A brief discussion of general techniques is presented below. 

There are numerous examples in the literature of fluorescence being used in place of ultraviolet light absorption as the end-point detection system for an immunoassay. In particular, methods using... 

Taking into consideration the great complexity of assay formats described in the literature, the following discussion will be limited to competitive immunoassays. The relevance of such limitation is supported by the data... 

Numerical data are a result of a literature search performed in the CAS database using the software SciFinder Scholar 2000. This search could not cover aU immunoassay publications, but was limited only to the ones in which the assay format (competitive or non-competitive) was specified. We consider, however, that the probability for the assay format to be mentioned is the same for both competitive and non-competitive immunoassays. 

According to the classification presented above, the equilibrium constants in immunoassays for environmental pollutants, most of which are relatively small hydrophobic molecules (potentially group A compounds), should not be considerably affected by the incubation temperature however, supporting data for such an assumption have, at least to our knowledge, not been presented in the literature yet. 

Kitamoto and Abe applied power ultrasonic waves (19.5 kHz, 600 W) to 300 ml of FeCh aqueous solution (pH 7.0) at 70 °C, and succeeded in encapsulating polyacrylate spheres of 250 nm diameter with magnetite ferrite coatings [49]. From TEM observations of the cross sections it was seen that the polymer spheres were covered with uniform columnar crystallites of 30-40 nm in diameter at the bottom and 60-70 nm at the top. The ultrasound waves produce OH groups on the polymer surfaces which work as ferrite nucleation sites this improves the quality of the ferrite coatings. The ferrite-encapsulated particles will greatly improve the performance of the enzyme immunoassay as a cancer test reagent. The above possible mechanism for the formation of the blue oxide is consistent with explanations in the literature for a sonochemical reaction. 

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