Tailoring spatiotemporal light confinement in single plasmonic nanoantennas

Plasmonic nanoantennas are efficient devices to concentrate light in spatial regions much smaller than the wavelength. Only recently, their ability to manipulate photons also on a femtosecond time scale has been harnessed. Nevertheless, designing the dynamical properties of optical antennas has been difficult since the relevant microscopic processes governing their ultrafast response have remained unclear. Here, we exploit frequency-resolved optical gating to directly investigate plasmon response times of different antenna geometries resonant in the near-infrared. Third-harmonic imaging is used in parallel to spatially monitor the plasmonic mode patterns. We find that the few-femtosecond dynamics of these nanodevices is dominated by radiative damping. A high efficiency for nonlinear frequency conversion is directly linked to long plasmon damping times. This single parameter explains the counterintuitive result that rod-type nanoantennas with minimum volume generate by far the strongest third-harmonic emission as compared to the more bulky geometries of bow-tie-, elliptical-, or disk-shaped specimens.

Effect of silica and hydroxyapatite mineralization on the mechanical properties and the biocompatibility of nanocomposite collagen scaffolds

A recently established materials concept of biomimetic composites based on silica, collagen, and calcium phosphates was adapted for the preparation of porous scaffolds suitable for tissue engineering applications. Mineralization was achieved by directed nucleation of silica on the templating organic phase during a sol-gel process with or without addition of hydroxyapatite. Both mineral phases (25 wt %, individually or combined in equal shares) influenced the scaffold's morphology at the nanoscale. Enhancement of apparent density and compressive strength was similar for silica or hydroxyapatite mineralization; however the stiffening effect of hydroxyapatite was much higher. All scaffold modifications provided proper conditions for adhesion, proliferation, and osteogenic differentiation of human bone marrow stromal cells. The open porosity allowed cells to migrate throughout the scaffolds while maintaining their viability, both confirmed by MTT staining and confocal laser scanning microscopy. Initial cell distributions were graduated due to collagen mineralization, but balanced out over the cultivation time of 28 days. RT-PCR analyses revealed higher gene expression of ALP but lower expression of BSP II and osteocalcin because of collagen mineralization. The results demonstrate that both silica and hydroxyapatite offer comparable possibilities to tailor mechanical properties of collagen-based scaffolds without being detrimental to in vitro biocompatibility.

[Surgical atrial fibrillation ablation therapy and postoperative monitoring]

Atrial fibrillation represents the most common atrial arrhythmia seen in clinical practice. The surgical treatment of atrial fibrillation is recommended in symptomatic patients as well as in asymptomatic patients at low postoperative risk. As a "stand alone" procedure, surgical ablation therapy is indicated after failed catheter ablation therapy, which occurs increasingly due to the high number of catheter-based ablation techniques. In order to gain acceptance among patients as well as referring cardiologists, the surgical ablation procedure ought to be performed in a minimally invasive fashion and with a very high success rate. When applied in an interdisciplinary approach by cardiologists/electrophysiologists and cardiothoracic surgeons, both ablative techniques have the potential to treat atrial fibrillation effectively and in the long-term. In order to document the true heart rhythm after ablation therapy, intermittent "snapshot" ECG documentation ought to be avoided. Small leadless devices that can be implanted subcutaneously enable full heart rhythm disclosure with documentation of atrial arrhythmias. The modern technique of implantable loop recorders permits individualized treatment for each patient.

Single defect centers in diamond nanocrystals as quantum probes for plasmonic nanostructures

We present two applications of a single nitrogen vacancy center in a nanodiamond as quantum probe for plasmonic nanostructures. Coupling to the nanostructures is achieved in a highly controlled manner by picking up a pre-characterized nanocrystal with an atomic force microscope and placing it at the desired position. Local launching of single excitations into a nanowire with a spatial control of few nanometers is demonstrated. Further, a two dimensional map of the electromagnetic environment of a plasmonic bowtie antenna was derived, resembling an ultimate limit of fluorescence lifetime nanoscopy.

Development of an osteoblast/osteoclast co-culture derived by human bone marrow stromal cells and human monocytes for biomaterials testing

The communication of bone-forming osteoblasts and bone-resorbing osteoclasts is a fundamental requirement for balanced bone remodelling. For biomaterial research, development of in vitro models is necessary to investigate this communication. In the present study human bone marrow stromal cells and human monocytes were cultivated in order to differentiate into osteoblasts and osteoclasts, respectively. Finally, a cultivation regime was identified which firstly induces the differentiation of the human bone marrow stromal cells followed by the induction of osteoclastogenesis through the osteoblasts formed--without the external addition of the factors RANKL and M-CSF. As a feedback on osteoblasts enhanced gene expression of BSP II was detected for modifications which facilitated the formation of large multinuclear osteoclasts. Phenotype characterization was performed by biochemical methods (DNA, LDH, ALP, TRAP 5b), gene expression analysis (ALP, BSP II, RANKL, IL-6, VTNR, CTSK, TRAP, OSCAR, CALCR) as well as light microscopy, confocal laser scanning microscopy, and scanning electron microscopy. After establishing this model on polystyrene, similar positive results were obtained for cultivation on a relevant bone substitution material--a composite xerogel of silica, collagen, and calcium phosphate.

Ultrabroadband background-free coherent anti-Stokes Raman scattering microscopy based on a compact Er:fiber laser system

We demonstrate a scheme for efficient coherent anti-Stokes Raman scattering (CARS) microscopy free of nonresonant background. Our method is based on a compact Er:fiber laser source. Impulsive excitation of molecular resonances is achieved by an 11 fs pulse at 1210 nm. Broadband excitation gives access to molecular resonances from 0 cm(-1) up to 4000 cm(-1). Time-delayed narrowband probing at 775 nm enables sensitive and high-speed spectral detection of the CARS signal free of nonresonant background with a resolution of 10 cm(-1).

In vitro osteoclastogenesis on textile chitosan scaffold

Textile chitosan fibre scaffolds were evaluated in terms of interaction with osteoclast-like cells, derived from human primary monocytes. Part of the scaffolds was further modified by coating with fibrillar collagen type I in order to make the surface biocompatible. Monocytes were cultured directly on the scaffolds in the presence of macrophage colony stimulating factor (M-CSF) and receptor activator of nuclear factor kappaB ligand (RANKL) for up to 18 days. Confocal laser scanning microscopy (CLSM) as well as scanning electron microscopy (SEM) revealed the formation of multinuclear osteoclast-like cells on both the raw chitosan fibres and the collagen-coated scaffolds. The modified surface supported the osteoclastogenesis. Differentiation towards the osteoclastic lineage was confirmed by the microscopic detection of cathepsin K, tartrate resistant acid phosphatase (TRAP), acidic compartments using 3-(2,4-dinitroanillino)-3'-amino-N-methyldipropylamine (DAMP), immunological detection of TRAP isoform 5b, and analysis of gene expression of the osteoclastic markers TRAP, cathepsin K, vitronectin receptor, and calcitonin receptor using reverse transcription-polymerase chain reaction (RT-PCR). The feature of the collagen-coated but also of the raw chitosan fibre scaffolds to support attachment and differentiation of human monocytes facilitates cell-induced material resorption--one main requirement for successful bone tissue engineering.