Adaptive subwavelength control of nano-optical fields

Adaptive shaping of the phase and amplitude of femtosecond laser pulses has been developed into an efficient tool for the directed manipulation of interference phenomena, thus providing coherent control over various quantum-mechanical systems. Temporal resolution in the femtosecond or even attosecond range has been demonstrated, but spatial resolution is limited by diffraction to approximately half the wavelength of the light field (that is, several hundred nanometres). Theory has indicated that the spatial limitation to coherent control can be overcome with the illumination of nanostructures: the spatial near-field distribution was shown to depend on the linear chirp of an irradiating laser pulse. An extension of this idea to adaptive control, combining multiparameter pulse shaping with a learning algorithm, demonstrated the generation of user-specified optical near-field distributions in an optimal and flexible fashion. Shaping of the polarization of the laser pulse provides a particularly efficient and versatile nano-optical manipulation method. Here we demonstrate the feasibility of this concept experimentally, by tailoring the optical near field in the vicinity of silver nanostructures through adaptive polarization shaping of femtosecond laser pulses and then probing the lateral field distribution by two-photon photoemission electron microscopy. In this combination of adaptive control and nano-optics, we achieve subwavelength dynamic localization of electromagnetic intensity on the nanometre scale and thus overcome the spatial restrictions of conventional optics. This experimental realization of theoretical suggestions opens a number of perspectives in coherent control, nano-optics, nonlinear spectroscopy, and other research fields in which optical investigations are carried out with spatial or temporal resolution.     

An integrated semiconductor device enabling non-optical genome sequencing

The seminal importance of DNA sequencing to the life sciences, biotechnology and medicine has driven the search for more scalable and lower-cost solutions. Here we describe a DNA sequencing technology in which scalable, low-cost semiconductor manufacturing techniques are used to make an integrated circuit able to directly perform non-optical DNA sequencing of genomes. Sequence data are obtained by directly sensing the ions produced by template-directed DNA polymerase synthesis using all-natural nucleotides on this massively parallel semiconductor-sensing device or ion chip. The ion chip contains ion-sensitive, field-effect transistor-based sensors in perfect register with 1.2 million wells, which provide confinement and allow parallel, simultaneous detection of independent sequencing reactions. Use of the most widely used technology for constructing integrated circuits, the complementary metal-oxide semiconductor (CMOS) process, allows for low-cost, large-scale production and scaling of the device to higher densities and larger array sizes. We show the performance of the system by sequencing three bacterial genomes, its robustness and scalability by producing ion chips with up to 10 times as many sensors and sequencing a human genome.     

Bone marrow genotoxicity of N-methyl, N-nitrosourea (NMU): n-alkanols as sister chromatid exchange (SCE) anti-inducers

The in vivo SCE test was used to demonstrate significant inhibition of NMU bone marrow genotoxicity by pretreatment of Chinese hamsters with n-alkanols. Our findings exclude a loss of intracellular DNA alkylation potential through a competitive direct reaction of NMU with the weakly nucleophilic polar end of the n-alkanols, but not through methylations of nucleophilic membrane sites possibly liberated by structural modifications which the membrane-active amphiphilics induce.     

Absorptionsspektrum von Melaninpigment

Summary The microphotometric absorptiometry of single isolated melanin granula and the photometric analysis of a KOH extract from a melanoblastoma metastasis show an extinction strongly increasing to the violet end of the spectrum, without any remarkable extinction maximum.

---

---

Die Arbeit wurde mit Unterstützung der Deutschen Forschungsgemeinschaft ausgeführt.     

Trans-complex formation by proteolipid channels in the terminal phase of membrane fusion

SNAREs (soluble N-ethylmaleimide-sensitive factor attachment protein receptors) and Rab-GTPases, together with their cofactors, mediate the attachment step in the membrane fusion of vesicles. But how bilayer mixing--the subsequent core process of fusion--is catalysed remains unclear. Ca2+/calmodulin controls this terminal process in many intracellular fusion events. Here we identify V0, the membrane-integral sector of the vacuolar H+-ATPase, as a target of calmodulin on yeast vacuoles. Between docking and bilayer fusion, V0 sectors from opposing membranes form complexes. V0 trans-complex formation occurs downstream from trans-SNARE pairing, and depends on both the Rab-GTPase Ypt7 and calmodulin. The maintenance of existing complexes and completion of fusion are independent of trans-SNARE pairs. Reconstituted proteolipids form sealed channels, which can expand to form aqueous pores in a Ca2+/calmodulin-dependent fashion. V0 trans-complexes may therefore form a continuous, proteolipid-lined channel at the fusion site. We propose that radial expansion of such a protein pore may be a mechanism for intracellular membrane fusion.     

Mutations in the polyglutamine binding protein 1 gene cause X-linked mental retardation

We found mutations in the gene PQBP1 in 5 of 29 families with nonsyndromic (MRX) and syndromic (MRXS) forms of X-linked mental retardation (XLMR). Clinical features in affected males include mental retardation, microcephaly, short stature, spastic paraplegia and midline defects. PQBP1 has previously been implicated in the pathogenesis of polyglutamine expansion diseases. Our findings link this gene to XLMR and shed more light on the pathogenesis of this common disorder.     

Hidden symmetries in the energy levels of excitonic 'artificial atoms'

Quantum dots or 'artificial atoms' are of fundamental and technological interest--for example, quantum dots may form the basis of new generations of lasers. The emission in quantum-dot lasers originates from the recombination of excitonic complexes, so it is important to understand the dot's internal electronic structure (and of fundamental interest to compare this to real atomic structure). Here we investigate artificial electronic structure by injecting optically a controlled number of electrons and holes into an isolated single quantum dot. The charge carriers form complexes that are artificial analogues of hydrogen, helium, lithium, beryllium, boron and carbon excitonic atoms. We observe that electrons and holes occupy the confined electronic shells in characteristic numbers according to the Pauli exclusion principle. In each degenerate shell, collective condensation of the electrons and holes into coherent many-exciton ground states takes place; this phenomenon results from hidden symmetries (the analogue of Hund's rules for real atoms) in the energy function that describes the multi-particle system. Breaking of the hidden symmetries leads to unusual quantum interferences in emission involving excited states.