With the demands of the high-throughput assay of biomarkers of ultralow concentrations in clinics, a 36-channel instrument utilizing immunomagnetic reduction (IMR) has been developed. The instrument involves the use of a high-T c superconducting-quantum-interference-device (SQUID) magnetometer to detect the signals due to the associations between target biomarker molecules and the antibody-functionalized magnetic nanoparticles in the reagent of IMR. In addition to illustrating the design and the measurements of the instrument, the assay characterizations for eight kinds of biomarkers related to neurodegenerative disease are investigated. Furthermore, the assay results among three independent instruments were compared. For an instrument, the channel-to-channel variations in measured concentrations of biomarkers are within a range of 2.09 to 5.62%. The assay accuracy was found to be from 99 to 103.7%. The p values in measured concentrations for any of the tested biomarkers were higher than 0.05 among the three instruments. The results demonstrate high throughput, high stability, and high consistency for the SQUID-IMR instruments.
Antibody-functionalized magnetic nanoparticles dispersed in phosphate-buffered saline solution were used as reagents in immunomagnetic reduction assays. Biomolecules are detected in bioliquid samples when they associate with magnetic nanoparticles and reduce the AC magnetic susceptibility χac of the reagent at a given frequency. In this study, the chemical kinetics for the real-time χac during the association was investigated. The association kinetics between biomolecules and nanoparticles consists of diffusion and binding steps. It was found that the diffusion speeds up in samples with higher concentrations of molecules. Furthermore, the period of association was longer for samples having higher concentrations of molecules. The association rates were proportional to the T-Tau concentration. The results showed that one biomolecule was associated with one magnetic nanoparticle.
<b><i>Background:</i></b> For assays using immunomagnetic reduction, a reagent composed of antibody-functionalized magnetic nanoparticles is dispersed in phosphate-buffered saline solution. The real-time signals of alternating-current (ac) magnetic susceptibility, χ<sub>ac</sub>, of the reagent are subsequently recorded after mixing the reagent with a biofluid sample. After mixing the reagent and sample, the reduction in χ<sub>ac</sub> of the mixture is calculated and used to quantify the concentration of the target biomarker in the sample. The reduction does not occur immediately but rather occurs at some time after mixing. This observation implies that the time elapsed before recording the real-time signals of χ<sub>ac</sub> of a reagent-sample mixture needs to be investigated to ensure that the signals are fully recorded. In this work, the effect of time to detection on the measured concentrations of proteins in human plasma after mixing the reagent and sample is examined. <b><i>Methods:</i></b> The proteins analyzed are related to Alzheimer’s disease: amyloid β 1–40, amyloid β 1–42, and Tau protein. The investigated times to detection after the mixing the reagent and sample are 0, 20, 30, 40, and 120 min. <b><i>Results:</i></b> The results show that the recording of real-time signals of χ<sub>ac</sub> should be conducted within 20 min after mixing the reagent and sample.
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