Magnetic nanoparticles (NPs) are increasingly being considered for use in biomedical applications such as biosensors, imaging contrast agents and drug delivery vehicles. In a biological fluid, proteins associate in a preferential manner with NPs. The small sizes and high curvature angles of NPs influence the types and amounts of proteins present on their surfaces. This differential display of proteins bound to the surface of NPs can influence the tissue distribution, cellular uptake and biological effects of NPs. To date, the effects of adsorption of a protein corona (PC) on the magnetic properties of NPs have not been considered, despite the fact that some of their potential applications require their use in human blood.Here, to investigate the effects of a PC (using fetal bovine serum) on the MRI contrast efficiency of superparamagnetic iron oxide NPs (SPIONs), we have synthesized two series of SPIONs with variation in the thickness and functional groups (i.e. surface charges) of the dextran surface coating. We have observed that different physico-chemical characteristics of the dextran coatings on the SPIONs lead to the formation of PCs of different compositions. 1 H relaxometry was used to obtain the longitudinal, r 1 , and transverse, r 2 , relaxivities of the SPIONs without and with a PC, as a function of the Larmor frequency. The transverse relaxivity, which determines the efficiency of negative contrast agents (CAs), is very much dependent on the functional group and the surface charge of the SPIONs' coating. The presence of the PC did not alter the relaxivity of plain SPIONs, while it slightly increased the relaxivity of the negatively charged SPIONs and dramatically decreased the relaxivity of the positively charged ones, which was coupled with particle agglomeration in the presence of the proteins. To confirm the effect of the PC on the MRI contrast efficiency, in vitro MRI experiments at n ¼ 8.5 MHz were performed using a low-field MRI scanner. The MRI contrasts, produced by different samples, were fully in agreement with the relaxometry findings.It is well-recognized that the surface of nanoparticles (NPs) is covered by biomolecules (proteins, sugars and lipids) upon coming into contact with biological systems, resulting in the formation of a protein "corona" that is strongly associated with the NPs' surface and that denes how living organisms (e.g. cells) "see" the NPs in a biological milieu. 1-5 According to previous reports, the cell "sees" a nano-system in which the NPs are covered by a "hard" corona of slowly exchanging proteins with a surrounding "so" corona consisting of weakly interacting and rapidly exchanging proteins. 6 The composition of the protein corona (PC) is highly dependent on the physicochemical properties of the NPs such as their size, composition, and surface characteristics. 7 Superparamagnetic iron oxide nanoparticles (SPIONs) have been recognized as very promising nanosystems with good biocompatibility 8,9 and high potential to be used for diagnosis and therapy simultaneou...

Magnetic resonance imaging (MRI) is at the forefront of non-invasive medical imaging techniques. It provides good spatial and temporal resolution that can be further improved by the use of contrast agents (CAs), providing a valuable tool for diagnostic purposes. Ultrasmall SuperParamagnetic Iron oxides (USPIOs) nanoparticles are attractive MRI contrast agents due to their negative (T 2 ) contrast enhancement capability and biocompatibility. Clusters of USPIOs with polymer material are of particular interest since they can sustain additional functionalities like drug delivery and targeting. Aiming to establish a relation between the cluster morphology and their efficacy as MRI contrast agent (relaxometric properties), we preparedby using three different maghemite (γ-Fe 2 O 3 ) USPIOs' diametersa series of hybrid copolymer/iron oxide CAs presenting two different geometries (micellar or vesicular). The NMR relaxometry profiles confirmed the nature of the physical mechanisms inducing the increased nuclear relaxation rates at low (magnetic anisotropy) and high (Curie relaxation) magnetic fields. A heuristic model, first proposed by Roch, Muller, Gillis, and Brooks, allowed the fitting of the whole longitudinal relaxivity r 1 () profile, for samples with different magnetic core sizes. We show that both types of cluster exhibit transverse relaxivity (r 2 ) values comparable or higher than those of common contrast agents, over the whole tested frequency range. Moreover, in-depth analysis revealed substantially a linear relation between r 2 and the number of encapsulated USPIOs divided by the diameter of the clusters (N USPIO /D H ), for each USPIOs size. The cluster structure (i.e. micelle or vesicle) appeared to have a mild influence on the transverse relaxivity value. Indeed, the r 2 value was mainly governed by the individual size of the USPIOs, correlated to both the cluster external diameter and the magnetic material volume fraction.

We implemented continuous-flow SABRE NMR spectroscopy on a chip, unlocking low-volume chemosensing of strongly diluted analytes.

1H-NMR relaxometric experiments over an extended frequency range show that ferrimagnetic colloidal nanoclusters exhibit enhanced transverse relaxivity, r2.

We present a systematic experimental comparison of the superparamagnetic relaxation time constants obtained by means of dynamic magnetic measurements and (1)H-NMR relaxometry, on ferrite-based nanosystems with different composition, various core sizes and dispersed in different solvents. The application of a heuristic model for the relaxivity allowed a comparison between the reversal time of magnetization as seen by NMR and the results from the AC susceptibility experiments, and an estimation of fundamental microscopic properties. A good agreement between the NMR and AC results was found when fitting the AC data to a Vogel-Fulcher law. Key parameters obtained from the model have been exploited to evaluate the impact of the contribution from magnetic anisotropy to the relaxivity curves and estimate the minimum approach distance of the bulk solvent.

We present (53)Cr-NMR spectra collected at low temperature in a single crystal of the heterometallic antiferromagnetic (AF) ring Cr(7)Ni in the S = 1/2 ground state with the aim of establishing the distribution of the local electronic moment in the ring. Due to the poor S/N we observed only one signal which is ascribed to three almost equivalent (53)Cr nuclei in the ring. The calculated spin density in Cr(7)Ni in the ground state, with the applied magnetic field both parallel and perpendicular to the plane of the ring, turns out to be AF staggered with the greatest component of the local spin for the Cr(3+) ions next to the Ni(2+) ion. The (53)Cr-NMR frequency was found to be in good agreement with the local spin density calculated theoretically by assuming a core polarization field of H(cp) = - 11 T/μ(B) for both orientations, close to the value found previously in Cr(7)Cd. The observed orientation dependence of the local spin moments is well reproduced by the theoretical calculation and evidences the importance of single-ion and dipolar anisotropies.

Combining microfluidic devices with nuclear magnetic resonance (NMR) has the potential of unlocking their vast sample handling and processing operation space for use with the powerful analytics provided by NMR....

We present a study of Y2-xZnxRu2O7 pyrochlores as a function of the Zn doping level x. X-ray diffraction measurements show that single-phase samples could be obtained for x < 0.2. Within the allowed range for x, DC conductivity measurements revealed a sizeable decrease in resistivity at all the investigated temperatures for Zn doped samples with respect to undoped ones. Neutron diffraction data of the x = 0.2 sample showed that replacing Y 3+ by Zn 2+ does not result in the formation of oxygen vacancies. X-ray photoemission spectroscopy measurements revealed that part of the Ru ions are in the 5+ oxidation state to balance, in terms of electronic charge, the incorporation of Zn 2+. The results give experimental evidence that the heterovalent doping promotes the increase of conductivity in the Y2Ru2O7 pyrochlores making these systems promising as intermediate temperature solid-oxide fuel cells cathodes.