No abstract

Polyfunctional hydrophilic microspheres of 125-nm diameter can be produced by copolymerization of acrylic monomers. Purified c-reactive protein (CRP) was covalently bound to these new micropheres, and the conjugate obtained was used as reagent in a microparticle-enhanced nephelometric immunoassay for human CRP. This assay was based on the measure, with a specially designed nephelometer, of the light scattered by aggregates formed during the immunoagglutination of the conjugate with anti-CRP antiserum. Sensitive inhibition of this agglutination by free CRP (6 ng/ml) allowed CRP quantitation in highly diluted serum samples (1/500-1/2,000), excluding any interference or sample pretreatment. The CRP assay was easy to perform (no washing or phase separation), reliable (coefficients of variation ranged from 1.3% to 9.3% for within-run and between-run determinations), and accurate (mean percentage of recovery: 104%; correlation coefficients with accepted analytical methods greater than or equal to 0.97) over a large range of concentrations. The inhibition mode excluded errors in the antigen excess zone and provided total security at high concentrations.

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Summary-A microparticle-enhanced nephelometric immunoassay of bovine immunoglobulins G is reported. lt is based on the nephelometric quantification of the competitive immunoagglutination of covalently coated microparticles. This new immunoassay is easy to perform (1-step, no sample pretreatment, no washing or phase separation), fast (1 h at most), sensitive (8 Ilgl1 of immunoglobulins G significantly detected in the reaction mixture), accu rate (linear recovery of immunoglobulins G in overloaded milks) and reproducible (CVs from 2.3-10% in within-and between-run precision studies). The potential of this microparticle-based immunoassay ls discussed with regard to the other quantitative immunoassays (radial immunodiffusion and convention al immunonephelometry in parneular) used in the determination of milk immunoglobulins G.