Magnetic force microscopy (MFM) is an atomic force microscopy (AFM) based technique in which an AFM tip with a magnetic coating is used to probe local magnetic fields with the typical AFM spatial resolution, thus allowing one to acquire images reflecting the local magnetic properties of the samples at the nanoscale. Being a well established tool for the characterization of magnetic recording media, superconductors and magnetic nanomaterials, MFM is finding constantly increasing application in the study of magnetic properties of materials and systems of biological and biomedical interest. After reviewing these latter applications, three case studies are presented in which MFM is used to characterize: (i) magnetoferritin synthesized using apoferritin as molecular reactor; (ii) magnetic nanoparticles loaded niosomes to be used as nanocarriers for drug delivery; (iii) leukemic cells labeled using folic acid-coated core-shell superparamagnetic nanoparticles in order to exploit the presence of folate receptors on the cell membrane surface. In these examples, MFM data are quantitatively analyzed evidencing the limits of the simple analytical models currently used. Provided that suitable models are used to simulate the MFM response, MFM can be used to evaluate the magnetic momentum of the core of magnetoferritin, the iron entrapment efficiency in single vesicles, or the uptake of magnetic nanoparticles into cells.

The pentanuclear PtII porphyrazine compound [(PtCl2)4LPt] (L = tetrakis-2,3-[5,6-di(2-pyridyl)pyrazino]porphyrazinato dianion), the mononuclear species [LPt] and the octacation [L′Pt]8+ (neutralized by I- ions; L′ = L octaquaternized at the pyridine N atoms) were synthesized and characterized by IR/UV-visible spectral measurements. 1H and 13C NMR spectral data on [(PtCl2)4 LPt] indicate that the four PtCl2 units are coordinated at the pyridine N atoms of the peripheral dipyridinopyrazine fragments ("py–py" coordination) and the largely prevalent conformational arrangement of the entire macrocycle, established to have the external N2(py)PtCl2 coordination sites all oriented on the same side with respect to the plane of the central porphyrazine framework, closely recalls that which was previously defined for the related PdII analog [(PdCl2)4LPd] . The currently investigated triad of PtII macrocycles, like the related PdII species, behave as photosensitizers for the generation of singlet oxygen, the cytotoxic agent active in photodynamic therapy (PDT). A bimodal anticancer potentiality is expressed by the pentaplatinated compound, [(PtCl2)4LPt] , which represents an unprecedented example of a multifunctional drug due to the presence of four contiguous cisplatin-like functionalities.

No abstract

High-resolution x-ray absorption near edge structure spectroscopy was used to characterize the metal sites in three different cobalt-substituted derivatives of Carcinus maenas hemocyanin (Hc), including a mononuclear cobalt, a dinuclear cobalt and a copper-cobalt hybrid derivative. Co(II) model complexes with structures exemplifying octahedral, trigonal bipyramidal, pseudo-tetrahedral, and square planar geometries were also studied. The results provide structural information about the metal binding site(s) in the Co-Hcs that extend earlier results from EPR and optical spectroscopy (Bubacco et al. 1992. Biochemistry. 31: 9294-9303). Experimental spectra were compared to those calculated for atomic clusters of idealized geometry, generated using a multiple scattering approach. The energy of the dipole forbidden 1s-->3d transition and of the absorption edge in the spectra for all cobalt Hc derivatives confirmed the cobaltous oxidation state which rules out the presence of an oxygenated site. Comparisons between data and simulations showed that the mononuclear and dinuclear Co(II) derivatives, as well as the hybrid derivative, contain four-coordinate Co(II) in distorted tetrahedral sites. Although the spectra for Co(II) in dinuclear metal sites more closely resemble the simulated spectrum for a tetrahedral complex than do spectra for the mononuclear derivative, the Co(II) sites in all derivatives are very similar. The Cu K-edge high resolution x-ray absorption near edge structure spectrum of the hybrid Cu-Co-Hc resembles that of deoxy-Hc demonstrating the presence of three-coordinate Cu(I).

The development of magnetic nanoparticles for biomedical applications requires a detailed characterization of their\ud magnetic properties, with relation not only to their chemical structure, but also their morphology and size. Magnetic force\ud microscopy (MFM), thanks to its nanometric lateral resolution and its capability to detect weak magnetic fields, appears as\ud a powerful tool for the characterization of the magnetic properties of single nanoparticles, together with their morphological\ud characteristics. Nevertheless, the application of MFM to the quantitative measurements of magnetic properties at the nanoscale\ud is still an open issue because of a certain incongruence between experimental data and existing theoretical models of the tip-\ud sample magnetic interactions. In this work, MFM data acquired on different magnetic nanoparticles in different experimental\ud conditions (magnetized and not magnetized probes, out-of-field and in-field measurements) are analyzed, with the aim of\ud individuating the possible phenomena affecting MFM measurements. These include topography-induced artifacts resulting\ud from the tip-sample capacitive coupling, which we propose here for the first time. In case of measurements performed in\ud presence of an external magnetic field, much more intense MFM signals were detected as it produces the saturation of the\ud magnetization of the nanoparticles, which is not completely obtained by the sole stray field produced by the tip. Nevertheless,\ud even in in-field measurements, the results evidenced the presence of significant electrostatic effects in MFM images, which,\ud therefore, appear as an important factor to be taken into account for the quantitative interpretation of MFM data

No abstract

Detecting stiff nanoparticles buried in soft biological matrices by atomic force microscopy (AFM) based techniques represents a new frontier in the field of scanning probe microscopies, originally developed as surface characterization methods. Here we report the detection of stiff (magnetic) nanoparticles (NPs) internalized in cells by using contact resonance AFM (CR-AFM) employed as a potentially non-destructive subsurface characterization tool. Magnetite (FeO) NPs were internalized in microglial cells from cerebral cortices of mouse embryos of 18 days by phagocytosis. Nanomechanical imaging of cells was performed by detecting the contact resonance frequencies (CRFs) of an AFM cantilever held in contact with the sample. Agglomerates of NPs internalized in cells were visualized on the basis of the local increase in the contact stiffness with respect to the surrounding biological matrix. A second AFM-based technique for nanomechanical imaging, i.e., HarmoniX™, as well as magnetic force microscopy and light microscopy were used to confirm the CR-AFM results. Thus, CR-AFM was demonstrated as a promising technique for subsurface imaging of nanomaterials in biological samples.

In our in vitro model, MNPs are taken up by granulocytes through phagocytosis, whereas previously described methods were based on the use of a chelating agent that permit Cu to cross the cell membrane. Moreover, the (64)Cu-engulfed granulocytes showed a high stability of up to 80% of retained radioactivity after 24 h of incubation.