SL participated in dielectric/magnetic

properties characterization and discussion and idea/experiment design. MGH carried out HRTEM and HAADF-STEM analysis, with XL assisting. LZ and HD carried out the magnetic property tests, with XL assisting. JL, YZ, and LKE helped to supervise the experiments and participated in the design of the study and manuscript revision. SO conceived of the study, supervised the project and experiments, and helped to write the manuscript. Pictilisib All authors read and approved the final manuscript.”
“Background Magnetic resonance imaging (MRI) is a powerful diagnostic modality for noninvasive in vivo imaging due to its high resolution, lack of exposure to radiation, superior soft tissue contrast, and large image window. However, it has less sensitivity than nuclear medicine and fluorescence imaging when monitoring small tissue lesions and molecular

or cellular activities [1]. Contrast agents (CAs) can improve the contrast and specificity in particular target regions of MR images, and these are widely used to produce brighter and darker areas with T1 and T2 CAs, respectively. T2 CAs, mainly based on iron oxide magnetic nanoparticles (MNPs), provide dark contrast in T2- or T2*-weighted (T2*-W) MR images depending on the T2 relaxivity of r 2 and the MNP concentration in the region of interest [2]. Superparamagnetic Wortmannin concentration iron oxide (SPIO) nanoparticles with diameters of 50 to 150 nm are thus the most commonly used MNPs in a variety of biomedical applications such as MRI contrast agents, induction of local hyperthermia, manipulation of cell membranes, biosensors, cell labeling and Reverse transcriptase tracking, and drug targeting and delivery [3–8]. SPIO particles have different physicochemical and biological properties, depending on the particle size and

coating PD-1/PD-L1 Inhibitor 3 molecular weight material, including MR T2 relaxivity r 2[9], cell labeling efficiency [10], cell cytotoxicity [11], and in vivo pharmacokinetics such as blood half-life and biodistribution [12]. Therefore, strategies by which uniform-sized biocompatible MNPs with long circulation times can be produced are highly sought after for nanomedical applications. There are two commonly used methods for synthesizing MNPs, organometallic [13] and aqueous solution coprecipitation [14]. In the organometallic approach, the particle size can be easily controlled [15]; however, the MNPs are only soluble in nonpolar and moderately polar organic solvents. This brings about the requirement for hydrophilic and biocompatible polymer coating to make them soluble enough for in vivo uses [16–18]. On the other hand, the aqueous solution coprecipitation method results in nanoparticles that are intrinsically water-soluble; however, the particle size distribution is relatively wide, resulting in nonuniform contrast in T2- or T2*-W MR images.