Nanopatterning of ferritin molecules and the controlled size reduction of their magnetic cores

Magnetic mapping of iron in rodent spleen

Evaluation of iron distribution and density in biological tissues is important to understand the pathogenesis of a variety of diseases and the fate of exogenously administered iron-based carriers and contrast agents. Iron distribution in tissues is typically characterized via histochemical (Perl's) stains or immunohistochemistry for ferritin, the major iron storage protein. A more accurate mapping of iron can be achieved via ultrastructural transmission electron microscopy (TEM) based techniques, which involve stringent sample preparation conditions. In this study, we elucidate the capability of magnetic force microscopy (MFM) as a label-free technique to map iron at the nanoscale level in rodent spleen tissue. We complemented and compared our MFM results with those obtained using Perl's staining and TEM. Our results show how MFM mapping corresponded to sizes of iron-rich lysosomes at a resolution comparable to that of TEM. In addition MFM is compatible with tissue sections commonly prepared for routine histology.

Magnetic force microscopy: quantitative issues in biomaterials

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.

A simple method for fabricating patterned curvilinear microstructures in poly(dimethylsiloxane) by selective wetting

The fabrication of patterned microstructures in poly(dimethylsiloxane) (PDMS) is a prerequisite for soft lithography. Herein, curvilinear surface relief microstructures in PDMS are fabricated through a simple three-stage approach combining microcontact printing (μCP), selective surface wetting/dewetting and replica molding (REM). First, using an original PDMS stamp (first-generation stamp) with linear relief features, a chemical pattern on gold substrate is generated by μCP using hexadecanethiol (HDT) as an ink. Then, by a dip-coating process, an ordered polyethylene glycol (PEG) polymer-dot array forms on the HDT-patterned gold substrate. Finally, based on a REM process, the PEG-dot array on gold substrate is used to fabricate a second-generation PDMS stamp with microcavity array, and the second-generation PDMS stamp is used to generate third-generation PDMS stamp with microbump array. These fabricated new-generation stamps are utilized in μCP and in micromolding in capillaries (MIMIC), allowing the generation of surface micropatterns which cannot be obtained using the original PDMS stamp. The method will be useful in producing new-generation PDMS stamps, especially for those who want to use soft lithography in their studies but have no access to the microfabrication facilities.

Directed assembly of P3HT:PCBM blend films using a chemical template with sub-300 nm features

Surface energy has been demonstrated as a means to direct interfacial-layer composition in polymer:fullerene blends utilized as active layers in organic photovoltaic devices. Combined with recent materials advances in the preparation of nanoscale chemical patterns, surface energy control of nanophase separation presents an opportunity to employ patterned surface energy templates to control the 3D blend morphology of polymer:fullerene blends. This report details the directed assembly of poly(3-hexylthiophene):phenyl-C61-butyric acid methyl ester (P3HT:PCBM) blends atop linear grating patterns with domains of alternating high and low surface energy of 50 to 600 nm in width prepared by nanoscale oxidative lithography of alkyl-terminated self-assembled monolayers on SiO2 and SiH surfaces. Tapping-, contact-, and current-sensing AFM studies demonstrated that chemical patterns were effective at directing the 3D morphology of P3HT:PCBM blends at dimensions of >200 nm. As the dimensionality of domains approached 100 nm, the chemical patterns were no longer able to direct phase segregation, evidence that a directed spinodal decomposition mechanism was responsible for the observed morphology. Surprisingly, the low surface energy component (P3HT) was found to be atop the high surface energy domains of the template, in conflict with current understanding of the role of surface energy directed assembly in polymer blends. These results suggest that the directed spinodal decomposition mechanism applies to conjugated polymer:fullerene blends, but that additional parameters unique to these types of systems will require refinement of the theory to adequately describe and predict the behavior of these scientifically and industrially interesting materials.