Nanoparticles composed of a magnetic iron oxide core surrounded by a metal shell have utility in a broad range of biomedical applications. However, the presence of surface energy differences between the two components makes wetting of oxide with metal unfavorable, precluding a “core–shell” structure of an oxide core completely surrounded by a thin metal shell. Three-dimensional island growth followed by island coalescence into thick shells is favored over the two-dimensional layer-by-layer growth of a thin, continuous metal coating of a true core–shell. Aqueous synthesis of gold-coated magnetite nanoparticles with analysis by infrared, energy-dispersive X-ray, and electron energy loss spectroscopies; high-resolution transmission electron microscopy; selected area electron diffraction; and high-angle annular dark-field scanning transmission electron microscopy showed two distinct morphologies that are inconsistent with an idealized core–shell. The majority were isolated ~16–22-nm-diameter nanoparticles consisting of ~7-nm-diameter magnetite and a thick deposition of gold, most often discontinuous, with some potentially “sandwiched” morphologies. A minority were aggregates of agglomerated magnetite decorated with gold but displaying significant bare magnetite. Both populations were successfully conjugated to fibrinogen and targeted to surface-activated platelets, demonstrating that iron oxide–gold nanoparticles produced by aqueous synthesis do not require an ideal core–shell structure for biological activity in cell labeling and targeting applications.

The immunogold technique is a valuable method for labeling cellular macromolecules. However, multiple labeling using colloidal gold (cAu) nanoparticles of different sizes presents certain drawbacks; namely, as particle size increases, there is a decreased labeling efficiency and diminished spatial resolution with respect to the locations of labeled epitopes. Both concerns also limit the utility of heavy metal particles for comparative analysis of labeling densities. To minimize the variables due to differential labeling efficiencies, the best solution would be to conduct multiple labeling with particles of similar size. Consequently, some parameter other than size is necessary to distinguish each label type. In this study, we report the synthesis of colloidal palladium (cPd) nanoparticles of similar size but having two distinct shapes, umbonate and faceted, which are readily distinguishable from spherical colloidal gold particles. Their utility and fidelity as labels using a human platelet whole-mount model is also demonstrated.

Correlative labeling permits colocalization of molecular species for observation of the same sample in light (LM) and electron microscopy (EM). Myosin bands in ultrathin cryosections were labeled using both fluorophore conjugated to secondary antibody (IgG) and colloidal gold (cAu) particles conjugated to primary IgG as reporters for LM and transmission electron microscopy (TEM), respectively. This technique allows rapid evaluation of labeling via LM, prior to more time-consuming observations with TEM and also yields two complementary data sets in one labeling procedure. Quenching of the fluorescent signal was inversely related to the distance between fluorophore and cAu particles. The signal from fluorophore conjugated to secondary antibody was inversely proportional to the size of cAu conjugated to primary antibody. Where fluorophore and cAu were bound to the same antibody, the fluorescence signal was nearly completely quenched regardless of fluorophore excitation or emission wavelength and regardless of particle size, 3 nm and larger. Colloidal metal particles conjugated to primary antibody provide high spatial resolution for EM applications. Fluorophore conjugated to secondary antibody provides spatial resolution well within that of conventional fluorescence microscopy. Use of fluorescent secondary antibody moved the fluorophore a sufficient distance from the cAu particles on the primary antibody to limit quenching of fluorescence.

The thin electron injection layers between the cathode and the light emitting polymer layer in polymer light emitting diodes (PLEDs) have been shown to have a big impact on the final device performance. Usually, in PLEDs low work function metals like Ba, Mg or Ca are used to reduce the energy barrier between the cathode and the polymer thus providing a better electron injection from the cathode. Also salts like LiF, NaF, Cs2CO3 and CsF have recently been shown to function as electron injection layers in light emitting devices. From these, especially caesium carbonate (Cs2CO3) results into high efficiency diodes both as a solution processed electron injection layer in PLEDs, as well as an n-dopant in the electron transport layer in vacuum deposited small molecule based OLEDs. The functional mechanism of Cs2CO3 as a pure interlayer is not yet fully understood. The proposed mechanisms include the n-doping of the organic layer with Cs2CO3, the thermal decomposition of Cs2CO3 and following formation of caesium metal or the formation of an n-doped CsO2 layer. In this study the phenomena resulting from the combination of a hole-dominant alkoxy-phenyl-substituted poly(phenylene vinylene) (PPV) based light emitting polymer with a highly efficient electron injection layer of Cs2CO3 in light emitting diodes has been investigated. As a result, diodes with about 35 % higher efficiency were achieved with PPV-Cs2CO3 structure in comparison to the traditional PPV-Ba structure. Additionally to the increased efficiency, also the lifetime of the Cs2CO3-diodes is comparable to the Ba-diodes implying that the long-term stability of the diodes is not affected by the optimized Cs2CO3-cathode. The strong increase in the electron injection of the Cs2CO3 diodes is apparently caused by a highly conductive, n-doped layer resulting from the charge transfer reaction between Cs2CO3 and PPV, where the magnitude of the reaction and resulting effects strongly depend on the amount of the applied Cs2CO3. The conclusion of the n-doped layer can be drawn from the LIV, impedance and photoluminescence measurements of the diodes with Ba and Cs2CO3 cathodes before, during and after electrical stressing.

Extended abstract of a paper presented at Microscopy and Microanalysis 2004 in Savannah, Georgia, USA, August 1–5, 2004.

Extended abstract of a paper presented at Microscopy and Microanalysis 2004 in Savannah, Georgia, USA, August 1–5, 2004.

Extended abstract of a paper presented at Microscopy and Microanalysis 2004 in Savannah, Georgia, USA, August 1–5, 2004.

We report on light extraction experiments with polyfluorene based organic light emitting diodes (OLEDs). The intensity distribution of emission within the substrate and within air is determined experimentally. For the devices investigated in this study, we find that the external quantum efficiency can be increased by a factor of 1.82, in the case of complete suppression of waveguiding within the substrate. The experimental data is in good agreement with modeling results based on dipole emission within a multilayer system. As a consequence of these findings, we modified the device topology by introducing light extraction structures between glass substrate and indium tin oxide anode. This results in redirection of photon trajectories and thus in a higher probability to extract waveguided radiation. At a luminance of 100 cd/m2, the photometric efficiency for emission in forward direction is enhanced by a factor of 1.45 to 8.9 cd/A.

Modulation of lymphocyte flow in the lymphatic compartment of the lymph node may serve, in part, to promote lymphocyte sensitization during an antigenic challenge. This study was undertaken to show where this might occur by examining the structural relationships of the intranodal lymphatic pathways, blood vessels, and connective tissue support with respect to lymphocyte and lymph flow. Differently stained plastic resins were injected into the blood vessels and lymphatics of the submandibular lymph node and visualized with a confocal laser scanning microscope. The specimens were corroded to study the three-dimensional cast structures by scanning electron microscopy. Alkali digestion was also used to prepare the reticular fiber network in the lymph node for scanning electron microscopic examination. At the hilus of the node, two to three arteries gave off arterioles running in medullary cords towards the cortex. The medullary cords, the periphery of the deep cortex, and the perifollicular zones had dense capillary networks. In contrast, the center of the follicle and the center of the deep cortex were less highly vascularized. High-endothelial venules were restricted to the perifollicular zone and the periphery of the deep cortex. At the cortico-medullary boundary, they abruptly transformed into medullary venules with a normal endothelium. The marginal sinus of the lymph node was crossed by thick reticular fibers that arose from the inner sheets of the capsule. The lymph pathway went through the marginal sinus, into the trabecular sinus, to the cortical perifollicular sinus, the dense lymphatic sinus around the deep cortex, and finally into the medullary sinus. At present, the exact functional significance of the complex lymph node lymphatic architecture is not clear. However, the highly organized structural organization may play a significant role in regulating and directing lymphocyte flow to facilitate antigen presentation.

Phagocytosis of particulate wear debris from arthroplasties by macrophages induces an inflammatory response that has been linked to implant loosening and premature failure of artificial joints. Inflammatory mediators released by phagocytic macrophages such as tumor necrosis factor-a (TNF-α), interleukin-1β (IL-1β), interleukin-6 (IL-6), and prostaglandin E2 (PGE2) are believed to play a central role in the pathogenesis of aseptic loosening. The objective of this study was to characterize titanium alloy particulates that closely match wear debris found around joint arthroplasties and to study their effects on the biosynthesis of inflammatory mediators by cultured monocytes. Peripheral blood monocytes were isolated from healthy human volunteers. Monocytes were cultured in 96-well plates for 24 h, washed, and exposed to three concentrations of titanium particulates and controls from 18Ð24 h. Supernatants were assayed for TNF-α, IL-1β, IL-6, and PGE2 activity. Energy dispersive X-ray spectroscopy (EDX) verified the titanium alloy to be Ti6A14V. Scanning electron microscopy (SEM) analysis showed significant titanium particulate heterogeneity with approximately 95% of the particles <1 micrometer in diameter. SEM and EDX technology was useful in the characterization of the titanium particulates utilized for in vitro models of titanium-induced cytokine release by monocytes. Incubation of titanium particulates (in concentrations similar to those found around loosened prosthetic joints) with cultured monocytes significantly increased their production of TNF-α, IL-1β, and PGE2.

Colloidal gold, conjugated to ligands or antibodies, is routinely used as a label for the detection of cell structures by light (LM) and electron microscopy (EM). To date, several methods to count the number of colloidal gold labels have been employed with limited success. Instrumental neutron activation analysis (INAA), a physical method for the analysis of the elemental composition of materials, can be used to provide a quantitative index of gold accumulation in bulk specimens. Given that gold is not naturally found in biological specimens in any substantial amount and that colloidal gold and ligand conjugates can be prepared to yield uniform bead sizes, the amount of label can be calculated in bulk biological samples by INAA. Here we describe the use of INAA, LM, transmission EM, and X-ray microanalysis (EDX) in a model to determine both distribution (localization) and amount of colloidal gold at the organ, tissue, cellular, and ultrastructural levels in whole animal systems following administration. In addition, the sensitivity for gold in biological specimens by INAA is compared with that of inductively coupled plasma-mass spectrometry (ICP-MS). The correlative use of INAA, LM, TEM, and EDX can be useful, for example, in the quantitative and qualitative tracking of various labeled molecular species following administration in vivo.

Microscopy continues to be a rapidly evolving field. Advances in instrumentation and image processing/analysis in traditional areas of TEM, SEM, and micro-analysis have taken place in tandem with developments in force-based microscopy and light microscopic imaging systems. MSA, through its programs and publications, has been evolving as well to meet the challenges and opportunities these advances provide for investigators in both the biological and physical sciences.