A comparative study of optical techniques applied to particle-enhanced assays of C-reactive protein.

This work is based on the well-established immunoassay principle of agglutination of latex particles covered by immunoproteins. In our experiments, positively charged particles act as carriers for the F(ab')2 fragment, obtained from rabbit polyclonal IgG, active against C-reactive protein (CRP). The presence of the antigen CRP in the immunolatex system causes agglutination and the aim of the present study was to compare different optical techniques (turbidimetry, nephelometry, angular anisotropy and photon correlation spectroscopy) capable of detecting the agglutination. The sensitivity and detection limit largely depend on the optical method. We have analyzed for each optical technique the following aspects: sensitivity, reproducibility, detection limit, reaction time, amount of sample wasted and availability of the required detection device. The results presented in this paper show that both angular anisotropy and photon correlation spectroscopy offer lower detection limits, and use little reagent, but have longer assay times than the classical optical techniques of turbidimetry and nephelometry.