Parallel optical readout of a cantilever array in dynamic mode

In this work we present parallel optical readout of a cantilever array which operates in dynamic mode using a standard optical beam deflection configuration containing only one laser-detector pair. We show accurate readout of the resonance frequency shift of an individual cantilever within an array by designing arrays where each cantilever has a different resonance frequency. The different resonance frequencies are created by giving each cantilever a different length and allow parallel readout of all cantilevers within the array. We show that even if the cantilevers are closely spaced each cantilever resonance frequency can be individually tracked without signs of cross-talk at current measurement precision (below 12 mHz). Interference of the laser light reflecting of each cantilever is observed when the amplitude of the cantilever is on the order of the wavelength of the laser light

Interactions between environmental stressors: the influence of salinity on host-parasite interactions between Daphnia magna and Pasteuria ramosa

Interactions between environmental stressors play an important role in shaping the health of an organism. This is particularly true in terms of the prevalence and severity of infectious disease, as stressors in combination will not always act to simply decrease the immune function of a host, but may instead interact to compound or even oppose the influence of parasitism on the health of an organism. Here, we explore the impact of environmental stress on host-parasite interactions using the water flea Daphnia magna and it is obligate parasite Pasteuria ramosa. Utilising an ecologically relevant stressor, we focus on the combined effect of salinity and P. ramosa on the fecundity and survival of the host, as well as on patterns of infectivity and the proliferation of the parasite. We show that in the absence of the parasite, host fecundity and survival was highest in the low salinity treatments. Once a parasite was introduced into the environment, however, salinity and parasitism acted antagonistically to influence both host survival and fecundity, and these patterns of disease were unrelated to infection rates or parasite spore loads. By summarising the form of interactions found in the broader Daphnia literature, we highlight how the combined effect of stress and parasitism will vary with the type of stressor, the trait used to describe the health of Daphnia and the host-parasite combination under observation. Our results highlight how the context-dependent nature of interactions between stress and parasitism inevitably complicates the link between environmental factors and the prevalence and severity of diseas

Microfabricated photoplastic cantilever with integrated photoplastic/carbon based piezoresistive strain sensor

L. Gammelgaard, P. A. Rasmussen, M. Calleja, P. Vettiger, and A. Boisen Department of Micro- and Nanotechnology, Technical University of Denmark, DK-2800 Kgs. Lyngby, Denmark We present an SU-8 micrometer sized cantilever strain sensor with an integrated piezoresistor made of a conductive composite of SU-8 polymer and carbon black particles. The composite has been developed using ultrasonic mixing. Cleanroom processing of the polymer composite has been investigated and it has been shown that it is possible to pattern the composite by standard UV photolithography. The composite material has been integrated into an SU-8 microcantilever and the polymer composite has been demonstrated to be piezoresistive with gauge factors around 15–20. Since SU-8 is much softer than silicon and the gauge factor of the composite material is relatively high, this polymer based strain sensor is more sensitive than a similar silicon based cantilever sensor.Peer reviewe

Monte Carlo transient phonons transport in silicon and germanium at nanoscales

Heat transport at nanoscales in semiconductors is investigated with a statistical method. The Boltzmann Transport Equation (BTE) which characterize phonons motion and interaction within the crystal lattice has been simulated with a Monte Carlo technique. Our model takes into account media frequency properties through the dispersion curves for longitudinal and transverse acoustic branches. The BTE collisional term involving phonons scattering processes is simulated with the Relaxation Times Approximation theory. A new distribution function accounting for the collisional processes has been developed in order to respect energy conservation during phonons scattering events. This non deterministic approach provides satisfactory results in what concerns phonons transport in both ballistic and diffusion regimes. The simulation code has been tested with silicon and germanium thin films; temperature propagation within samples is presented and compared to analytical solutions (in the diffusion regime). The two materials bulk thermal conductivity is retrieved for temperature ranging between 100 K and 500 K. Heat transfer within a plane wall with a large thermal gradient (250 K-500 K) is proposed in order to expose the model ability to simulate conductivity thermal dependence on heat exchange at nanoscales. Finally, size effects and validity of heat conduction law are investigated for several slab thicknesses

Shining light on T6SS mode of action and function within single cells and bacterial communities

Bacteria are ubiquitously found in the environment and form the basis for all known ecosystems on our planet. Most bacterial cells reside in complex multi-species bacterial communities, which are often associated with a host, such as the human microbiota. These bacterial communities are shaped by cooperative and competitive interactions amongst their members. Like higher animals, bacteria also compete with their conspecifics for nutrients and space. This evolutionary arms race resulted in a diverse set of strategies for microbial competition. In particular, bacteria residing on solid surfaces can compete with their neighbors through the use of specialized nanomachines, called secretion systems, enabling the direct delivery of toxic effector molecules into by-standing target cells. The most commonly used weapon for contact-dependent antagonism is the bacterial Type VI secretion system (T6SS). The T6SS belongs to the family of contractile injection systems (CISs). All CISs are structurally and functionally related to contractile bacteriophages (e.g. phage T4) and translocate proteins into target cells by means of physical force, which is generated by rapid sheath contraction. This results in the ejection of the inner tube associated with a sharp tip and effector proteins at its end. Effector translocation leads ultimately to target cell death. Importantly, the T6SS is capable translocating effectors across broad ranges of biological membranes making it a powerful weapon in microbial warfare as well as potent virulence mechanism towards eukaryotic host cells. Our current understanding of T6SS mode of action is primarily based on the combination of structural biology and fluorescence live-cell microscopy studies. While in particular cryo-electron microscopy (cryo-EM) revealed the detailed architecture of the T6SS in situ and of isolated subassemblies, fluorescence live-cell microscopy uncovered the remarkable dynamics of T6SS biogenesis. However, a complete understanding of T6SS dynamics is hampered in standard fluorescent microscopy due to: (i) the spatial and temporal resolution limit, (ii) the inability to efficiently label secreted components of the machinery, (iii) the weak signals due to low protein abundance and rapid photobleaching, (iv) the difficulty to perform long-term co-incubation experiments as well as (v) the inability to precisely control spatial and chemical environment. My doctoral thesis aimed to overcome these limitations to allow novel insights into dynamics of the T6SSs of Vibrio cholerae, Pseudomonas aeruginosa and Acinetobacter baylyi. Specifically sheath assembly, initiation of sheath contraction, T6SS mediated protein translocation in to sister cells as well as strategies for prey cell inhibition were studied in this thesis. First, I studied sheath assembly in ampicillin induced V. cholerae spheroplasts. These enlarged cells assemble T6SS sheaths which are up to 10x longer as compared to rod shaped cells. This allowed us to photobleach an assembling sheath structure and demonstrate that new sheath subunits are added to the growing sheath polymer at the distal end opposite the baseplate. Importantly, this was the first direct observation made for any contractile machines studied to date. Moreover, I showed that unlike for all other CISs, T6SS sheath length is not regulated and correlates with cell size. In order to monitor protein translocation into target cells, we developed a T6SS dependent interbacterial protein complementation assay, enabling the indirect detection of translocated T6SS components into the cytosol of recipient cells. This allowed us to demonstrate that secreted T6SS components are exchanged among by-standing sister cells within minutes upon initial cell contact. Importantly, these results were the first experimental indication that T6SS is capable of translocating its components into the cytosol of Gram-negative target cells. Furthermore, we showed that the amount and the composition of the secreted tip influences the number of T6SS assemblies per cell, whereas different concentration of the tube protein influenced sheath length. We also provided evidence that precise aiming of T6SS assemblies through posttranslational regulation in P. aeruginosa increases the efficiency of substrate delivery. In addition, together with two Nanoscience master students we have also been implementing microfluidics in the Basler laboratory. This powerful technology enabled us to control the spatial arrangements of aggressor and prey populations and to follow these populations at single-cell level over time scales of several hours. In collaboration with Prof. Kevin Forster, University of Oxford, we demonstrated that the rate of target cell lysis heavily influences the outcome of contact-dependent T6SS killing and thus drives evolution of lytic effectors. Moreover, microfluidics allows for the dynamic change of the chemical microenvironment during imaging experiments. By following the T6SS dynamics in response to hyperosmotic shocks resulting in a rapid cell volume reduction, we found that physical pressure from the collapsing cell envelope could trigger sheath contraction. This led us to propose a model for sheath contraction under steady-state conditions where continued sheath polymerization against membrane contact site leads to a gradual increase in pressure applied to the assembled sheath. We propose that this could be potentially sensed by the baseplate, which in turn would trigger sheath contraction

Atomic Scale Memory at a Silicon Surface

The limits of pushing storage density to the atomic scale are explored with a memory that stores a bit by the presence or absence of one silicon atom. These atoms are positioned at lattice sites along self-assembled tracks with a pitch of 5 atom rows. The writing process involves removal of Si atoms with the tip of a scanning tunneling microscope. The memory can be reformatted by controlled deposition of silicon. The constraints on speed and reliability are compared with data storage in magnetic hard disks and DNA.Comment: 13 pages, 5 figures, accepted by Nanotechnolog

Dual Role for DsbA in Attacking and Targeted Bacterial Cells during Type VI Secretion System-Mediated Competition

Incorporation of disulfide bonds into proteins can be critical for function or stability. In bacterial cells, the periplasmic enzyme DsbA is responsible for disulfide incorporation into many extra-cytoplasmic proteins. The type VI secretion system (T6SS) is a widely occurring nanomachine that delivers toxic effector proteins directly into rival bacterial cells, playing a key role in inter-bacterial competition. We report that two redundant DsbA proteins are required for virulence and for proper deployment of the T6SS in the opportunistic pathogen Serratia marcescens, with several T6SS components being subject to the action of DsbA in secreting cells. Importantly, we demonstrate that DsbA also plays a critical role in recipient target cells, being required for the toxicity of certain incoming effector proteins. Thus we reveal that target cell functions can be hijacked by T6SS effectors for effector activation, adding a further level of complexity to the T6SS-mediated inter-bacterial interactions which define varied microbial communities

Au-Ag template stripped pattern for scanning probe investigations of DNA arrays produced by Dip Pen Nanolithography

We report on DNA arrays produced by Dip Pen Nanolithography (DPN) on a novel Au-Ag micro patterned template stripped surface. DNA arrays have been investigated by atomic force microscopy (AFM) and scanning tunnelling microscopy (STM) showing that the patterned template stripped substrate enables easy retrieval of the DPN-functionalized zone with a standard optical microscope permitting a multi-instrument and multi-technique local detection and analysis. Moreover the smooth surface of the Au squares (abput 5-10 angstrom roughness) allows to be sensitive to the hybridization of the oligonucleotide array with label-free target DNA. Our Au-Ag substrates, combining the retrieving capabilities of the patterned surface with the smoothness of the template stripped technique, are candidates for the investigation of DPN nanostructures and for the development of label free detection methods for DNA nanoarrays based on the use of scanning probes.Comment: Langmuir (accepted

Production Planning, Scheduling and SME

Small and medium-sized enterprises (SME) are the backbone of central Europe's economies and have a significant contribution to the gross domestic product. Production planning and scheduling (PPS) is still a crucial element in manufacturing industries of the 21st century even though this area of research is more than a century old. The topic of PPS is well researched especially in the context of large enterprises in the manufacturing industry. However, the implementation of PPS methodologies within SME is mostly unobserved. This work analyzes how PPS is implemented in SME with the geographical focus on Switzerland and its vicinity. Based on restricted resources compared to large enterprises, SME have to face different challenges. The real problem areas of selected enterprises in regards of PPS are identified and evaluated. For the identified real-life problem areas of SME clear and detailed recommendations are created, covering concepts and best practices and the efficient usage of PPS. Furthermore, the economic and entrepreneurial value for companies is lined out and why the implementation of the introduced recommendations is advised