Microfluidic-Based Synthesis of Magnetic Nanoparticles Coupled with Miniaturized NMR for Online Relaxation Studies

Using compact desktop NMR systems for rapid characterization of relaxation properties directly after synthesis can expedite the development of functional magnetic nanoparticles. Therefore, an automated system that combines a miniaturized NMR relaxometer and a flow-based microreactor for online synthesis and characterization of magnetic iron oxide nanoparticles is constructed and tested. NMR relaxation properties are quantified online with a 0.5 T permanent magnet for measurement of transverse (T₂) and longitudinal (T₁) relaxation times. Nanoparticles with a primary particle size of about 25 nm are prepared by coprecipitation in a tape-based microreactor that utilizes 3D hydrodynamic flow focusing to avoid channel clogging. Cluster sizes are expeditiously optimized for maximum transverse relaxivity of 115.5 mM s^-1. The compact process control system is an efficient tool that speeds up synthesis optimization and product characterization of magnetic nanoparticles for nanomedical, theranostic, and NMR-based biosensing applications.