Flow-immunoassay methods

As a POC (point of care) device semi-quantitative flow-immunoassay methods for the detection of antibodies or antigens had been developed and are well establish in e.g. pregnancy tests. This format is also known as strip test, one step strip test, immunochromatographic test, rapid flow diagnostic, rapid immunoassay or lateral flow immunoassay (LFI). The label is anyway a colored colloidal particle. Additionally to metal colloids, carbon (black) and silica or latex (various colors) are in use. 

Immunoassay methods involving adsorption of antigen by charcoal particles were found to be unsuitable for use with microfiltration techniques. The fine particles quickly block the glass fiber, with a sharp drop in the flow rate, so that variable amounts of the supernatant are retained with the precipitate. 

Kusterbeck A W, Wemhoff GA, Charles PT, et al. 1990. A continuous-flow immunoassay for rapid and sensitive detection of small molecules. J Immunol Methods 135 191-197. 

Flow-based analytical procedures are already used in many fields, e.g., environment, food and health. In tandem with the developments described above, flow analysers will also be used in new and emerging fields of application such as the "omics" (metallomics, genomics and proteomics), biotechnology (enzymatic assays, platforms for bio-sensors and flow immunoassays) and quality-control applications in general. Economic resources will also be a driver for more multi-parametric flow-based methods, particularly with spectrophotometric detection. 

Oku, Y., Kamiya, K., Kamiya, H., Shibahara, Y., Ii, T., and Uesaka, Y. (2001) Development of oligonucleotide lateral-flow immunoassay for multi-parameter detection. J. Immunol. Methods 258, 73-84... 

The reliability of the test strip immunoassay was determined by carrying out the test with the uncontaminated samples spiked with detected target at three levels and analyzed by strip test and instrumental analysis. The results obtained by strip test should be consistent with the results obtained by instrument. The correlation between the two methods should be good. An example of validation of gold-based lateral flow immunoassay and analysis of food samples for the detection of carbaryl was shown in the following. 

Nadanaciva S, Willis JH, Barker ML, Gharaibeh D, Capaldi RA, Marusich MF, Will Y (2009) Lateral-flow immunoassay for detecting drug-induced inhibition of mitochondrial DNA repb-cation and mtDNA-encoded protein synthesis. J Immunol Methods, 343, 1-12. 

Figure 5 Laterai flow membrane device for residue testing. S, sampie weii T, test iine C, controi iine. (Reproduced from O Keeffe M, Crabbe P, Saiden M, etal. (2003) Preiiminary evai-uation of a iaterai flow immunoassay device for screening urine sampies for the presence of suiphamethazine. Journal of Immunological Methods 278 117-126.)...

Most of the immunoassay methods for bacterial detection are currently performed in solid-phase ELISA format conducted on micro-titer plates. Flow inununofiltration assay, can be an excellent alternative for detection of bacterial pathogens because it not only overrides the effects of diffusional limitations in conventional ELISA, but also allows the concentration of bacteria on the membrane by filtering a large volume of... 

The ICMs used for pesticide analysis include immimoassays (lAs) and the use of antibodies for sample preparation (e.g., for SPE and the cleanup of samples) [153], detection in flow-injection analysis, and biosensors. The earliest ICMs to be developed for pesticides analysis were lAs. There are various t) es of lAs, but the most frequently used in this context is the enzyme-linked immunosorbent assay (ELISA) [185]. ELISA is a heterogeneous assay because the antibodies or antigens are immobilized on a solid phase. Table 18.3 lists selected ELISA methods for the determination of pesticides in water samples [186-190]. Bjamason et al. have proposed an enzyme flow immunoassay (EFIA) using a protein G column for the determination of triazine herbicides in surface and wastewaters with a linear range between 0.1 and 10 pg/L [191]. 

Most of the reported methods of analysis of valproic acid and its sodium salt in biological fluids rely on the use of chromatography, especially gas chromatography, although high performance liquid chromatography (HPLC) is also reported. Other methods, such as flow injection analysis, enzyme-immunoassay, fluorescence-polarization capillary electrophoresis, and potentiometry are sometimes used. The reported methods can be classified as follows. 

Applying different CL systems, continuous-flow CL-based detection of several analytes has been widely applied for determination of several biological compounds and drugs. This technique has already become a highly sensitive method of detection in FIA, in liquid and gas chromatography, and in immunoassays [6-12],... 

As a process analytical solution, these extrinsic reactive approaches necessitate an extrinsic optode (see later discussion), an on-line sample conditioning system or an at-Une solution such as a flow injection analysis (FIA) system or other autonomous solutions. Reaction kinetics, post analysis cleanup such as rejuvenating a substrate (optode, immobilized based immunoassays, etc.) among other complexities are additional considerations for these types real-time analysis methods. ... 

As already discnssed, intrinsic LIF bioreactor monitoring is the most common application within biopharmaceutical manufacturing. Other extrinsic PAT LIF methods are also possible for biopharmacenticals snch as varions flnorescence immunoassays facilitated by flow injection analysis " or other real-time approaches. As PAT begins to emerge within biopharmaceuticals the wider used of sensitive and precise in-line intrinsic and extrinsic approaches such as optodes and at-line extrinsic methods is likely to occnr. ... 

The utilization of lAC in analytical methods has received increasing retention in recent years [23,24], Of particular interest is the use of immobilized antibody columns in performing immunoassays, a technique known as a chromatographic immunoassay or flow-injection immunoassay. This approach has already been reported in a number of formats such as those involving simple analyte adsorption/desorption, sandwich immunoassays, competitive binding immunoassays, and multianalyte methods (see Figure 13,9) [23,24,73,74], Typical advantages of these methods include decreased analysis times and improved precision versus manual immunoassays. 

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