Use of magnetic nanoparticles and a microplate reader with fluorescence detection to detect C-reactive protein

Two approaches based on magnetic nanoparticles (MNPs) have been compared to analyze C-reactive protein (CRP). Both the non-eluted and eluted MNP-1°Ab-CRP-2°Ab/FITC bioconjugates were measured by a microplate reader with fluorescence detection. The linear ranges for the non-elution and elution methods were 10-200 and 0.1-2.0 μg/mL, respectively. The concentration limits of detection for the nonelution and elution methods were 2.91 and 0.04 μg/mL, respectively. The non- elution method gave better precision and recovery than the elution method, and also showed comparable results to that of ELISA assay. The non-elution method is simple and only needs minute volumes of sample and buffer. There is no need to dissociate the fluorescence probes from the bioconjugates, and the fluorescence signals can be directly measured on the MNP-1°Ab-CRP-2°Ab/FITC bioconjugates. Meanwhile, samples with high CRP concentrations are not necessarily to be diluted before analysis. In this study, CRP has been used as a model analyte for comparison of the non-elution and elution methods using MNPs and a microplate reader. The results of this study would help for the development of a sensitive immunoassay using the non-elution method. Meanwhile, high throughput analysis of inflammatory serum proteins is feasible since a microplate reader is used. Further experiments can be performed to reduce the incubation times, to further decrease the concentration limit of detection, and to reduce the non-specific interactions between the two antibodies when the target analyte concentration is relatively low.