Minispec mq 40

All measurements were performed at 40 °C and 40 MHz (0.94 T) using an MR spectrometer (Minispec mq 40; Bruker Karlsruhe, Germany). Diluted nanoparticle solutions with iron concentrations between 0.1 and 1.5 mmol/L were prepared. Three solutions with different concentrations were measured for each sample. The relaxation coefficients R₁ and R₂ were obtained by linear fitting of T₁ and T₂ relaxation rates, and values were normalized to the iron concentrations.

We here focused on T1 relaxivity only. The determination of proton T1 relaxation rates was performed at 40 °C and 40 MHz (0.94 T) using an MR spectrometer (Minispec mq 40; Bruker, Karlsruhe, Germany). T1 relaxation rates were determined with an inversion recovery pulse sequence, which is the standard measuring and analysis method of the equipment.
Measurements were performed in nanopure water containing 0.009% NaCl. For the determination of T1 relaxivities of VSOPs with and without the presence of EVs, VSOPs at a constant concentration of 0.0188 mM were mixed with different EV concentrations (protein contents between 0 and 5.0 µg/mL). Three solutions with different concentrations were measured for each sample. The relaxivity coefficients r1 were obtained by linear fitting of T1 relaxation rates, and values were normalized to the iron concentrations.