Core size distribution estimation of magnetic nanoparticles in hydrogel matrix: Analysis of diamagnetic interference and correction strategy

The core size distribution is a critical parameter determining the performance of magnetic nanoparticles (MNPs) in biomedical applications. In this study, the magnetic interference of the hydrogel matrix on the core size estimation was investigated. It was identified that the matrix generates a diamagnetic response that superimposes on the superparamagnetic response of the MNPs. This superposition results in a distortion of the static magnetization curve, particularly in the high-field region. Consequently, the core size distribution estimated from the uncompensated magnetization deviates significantly from the true value. To address this issue, an improved method is proposed to accurately estimate the core size distribution by compensating for the matrix interference. Based on the identified superposition characteristic, a compensation model was established to subtract the diamagnetic contribution and recover the intrinsic magnetization of the MNPs. Experimental results demonstrate that the core size distribution estimated using the proposed compensation method is significantly more accurate than that obtained directly from composite magnetization, demonstrating the necessity of this strategy for the precise characterization of MNPs in hydrogel-based biomimetic environments.