Theoretical Explorations of Reductions in The Alternative-current Magnetic Susceptibility of Reagent in Immunomagnetic Reduction Assay

Yang SY

Published on: 2024-09-30

Abstract

Given the demands of ultrasensitive immunoassays for early diagnosis, a technology called immunomagnetic reduction (IMR) using antibody-functionalized magnetic nanoparticles has been developed. Many experimental results have revealed decreases in the alternative-current (AC) magnetic susceptibility of the reagent when antibody-functionalized magnetic nanoparticles bind to target protein molecules. However, the physical mechanism underlying the reduction in AC magnetic susceptibility in the IMR assay is not clear. In this work, the AC magnetic susceptibility of the reagent used in the IMR assay was explored theoretically to elucidate the physical mechanism. The time constant of Brownian relaxation is prolonged for nanoparticles bound to protein molecules, resulting in a phase delay in the AC magnetic susceptibility of bound nanoparticles with respect to that of unbound nanoparticles. The phase delay is attributed to the observed decrease in the AC magnetic susceptibility of the reagent used in the IMR assay. Further analysis demonstrated that the phase delay and decrease in the AC magnetic susceptibility of the reagent are greater for larger molecules or higher protein concentrations, which is quantitatively consistent with the experimental observations.