Simple size tuning of magnetic nanoparticles using a microwave solvothermal method and their application in facilitating the solid-phase synthesis of molecularly imprinted polymers

Abstract

Herein, we have demonstrated a simple, economical, rapid and scalable microwave method to produce magnetite-based magnetic nanoparticles (MNPs) with desired sizes and their application in the facile synthesis of high-value polymer products. Solvothermal method is gaining traction in microwave synthesis as it offers a rapid and green method for MNP production. In this work, we report a novel, simple and reliable microwave synthesis method, where adjusting the temperature gradient from 20 °C to a dwell temperature of 200 °C enabled the size control of superparamagnetic aldehyde-functionalised nanoparticles (MNP@CHO). The size distribution of nanoparticles was measured using dynamic light scattering, which revealed values of 14 nm ± 8 nm at 90 °C min⁻¹ (a 2-minute ramp time to dwell temperature) and 122 nm ± 49 nm at 18 °C min⁻¹ (a 10-minute ramp time to dwell temperature), and these nanoparticles were produced within 20–30 minutes. Magnetic size analysis using the Chantrell method confirmed that the iron–oxide core size increased as a function of ramp time, with the median diameter in the range of 7.91 to 11.25 nm and lognormal σ values within 0.22 ≤ σ ≤ 0.33. The particle cluster size increased with an increase in the ramp time, which was measured using transmission electron microscopy, and it was found to be a function of particle agglomeration. Furthermore, we demonstrated that MNP@CHO functionalised with a protein of interest can be applied for the rational solid-phase synthesis of molecularly imprinted polymer nanoparticles (nanoMIPs) with high affinity for protein biomarkers. Thus, we demonstrated that an optimal MNP size is required for the highly efficient production of MNP-based nanoMIPs, which is the key to the mass production and commercialisation of low-cost and sustainable size-tuned MNPs and artificial antibodies.