Mechanical Characterization of PDMS Films for the Optimization of Polymer Based Flexible Capacitive Pressure Microsensors

This paper reports on the optimization of flexible PDMS-based normal pressure capacitive microsensors dedicated to wearable applications. The operating principle and the fabrication process of such microsensors are presented. Then, the deformations under local pressure of PDMS thin films of thicknesses ranging from 100 μm to 10 mm are studied by means of numerical simulations in order to foresee the sensitivity of the considered microsensors. The study points out that, for a given PDMS type, the sensor form ratio plays a major role in its sensitivity. Indeed, for a given PDMS film, the expected capacitance change under a 10 N load applied on a 1.7 mm radius electrode varies from a few percent to almost 40% according to the initial PDMS film thickness. These observations are validated by experimental characterizations carried out on PDMS film samples of various thicknesses (10 μm to 10 mm) and on actual microsensors. Further computations enable generalized sensor design rules to be highlighted. Considering practical limitations in the fabrication and in the implementation of the actual microsensors, design rules based on computed form ratio optimization lead to the elaboration of flexible pressure microsensors exhibiting a sensitivity which reaches up to 10%/N

Characterization of Flexible RF Microcoil Dedicated to Surface Mri

In Magnetic Resonance Imaging (MRI), to achieve sufficient Signal to Noise Ratio (SNR), the electrical performance of the RF coil is critical. We developed a device (microcoil) based on the original concept of monolithic resonator. This paper presents the used fabrication process based on micromoulding. The dielectric substrates are flexible thin films of polymer, which allow the microcoil to be form fitted to none-plane surface. Electrical characterizations of the RF coils are first performed and results are compared to the attempted values. Proton MRI of a saline phantom using a flexible RF coil of 15 mm in diameter is performed. When the coil is conformed to the phantom surface, a SNR gain up to 2 is achieved as compared to identical but planar RF coil. Finally, the flexible coil is used in vivo to perform MRI with high spatial resolution on a mouse using a small animal dedicated scanner operating at in a 2.35 T.Comment: Submitted on behalf of TIMA Editions (http://irevues.inist.fr/tima-editions

Human topoisomerase IIα uses a two-metal-ion mechanism for DNA cleavage

The DNA cleavage reaction of human topoisomerase IIα is critical to all of the physiological and pharmacological functions of the protein. While it has long been known that the type II enzyme requires a divalent metal ion in order to cleave DNA, the role of the cation in this process is not known. To resolve this fundamental issue, the present study utilized a series of divalent metal ions with varying thiophilicities in conjunction with DNA cleavage substrates that replaced the 3′-bridging oxygen of the scissile bond with a sulfur atom (i.e. 3′-bridging phosphorothiolates). Rates and levels of DNA scission were greatly enhanced when thiophilic metal ions were included in reactions that utilized sulfur-containing substrates. Based on these results and those of reactions that employed divalent cation mixtures, we propose that topoisomerase IIα mediates DNA cleavage via a two-metal-ion mechanism. In this model, one of the metal ions makes a critical interaction with the 3′-bridging atom of the scissile phosphate. This interaction greatly accelerates rates of enzyme-mediated DNA cleavage, and most likely is needed to stabilize the leaving 3′-oxygen

Lab-on-chip for in situ analysis of nutrients in the deep sea

Microfluidic reagent-based nutrient sensors offer a promising technology to address the global undersampling of ocean chemistry but have so far not been shown to operate in the deep sea (>200 m). We report a new family of miniaturized lab-on-chip (LOC) colorimetric analyzers making in situ nitrate and phosphate measurements from the surface ocean to the deep sea (>4800 m). This new technology gives users a new low-cost, high-performance tool for measuring chemistry in hyperbaric environments. Using a combination of laboratory verification and field-based tests, we demonstrate that the analyzers are capable of in situ measurements during profiling that are comparable to laboratory-based analyses. The sensors feature a novel and efficient inertial-flow mixer that increases the mixing efficiency and reduces the back pressure and flushing time compared to a previously used serpentine mixing channel. Four separate replicate units of the nitrate and phosphate sensor were calibrated in the laboratory and showed an average limit of detection of 0.03 μM for nitrate and 0.016 μM for phosphate. Three on-chip optical absorption cell lengths provide a large linear range (to >750 μM (10.5 mg/L-N) for nitrate and >15 μM (0.47 mg/L-P) for phosphate), making the instruments suitable for typical concentrations in both ocean and freshwater aquatic environments. The LOC systems automatically collected a series of deep-sea nitrate and phosphate profiles in the northeast Atlantic while attached to a conductivity temperature depth (CTD) rosette, and the LOC nitrate sensor was attached to a PROVOR profiling float to conduct automated nitrate profiles in the Mediterranean Sea

Carbon nanotubes allow capture of krypton, barium and lead for multichannel biological X-ray fluorescence imaging

The desire to study biology in situ has been aided by many imaging techniques. Among these, X-ray fluorescence (XRF) mapping permits observation of elemental distributions in a multichannel manner. However, XRF imaging is underused, in part, because of the difficulty in interpreting maps without an underlying cellular ‘blueprint’; this could be supplied using contrast agents. Carbon nanotubes (CNTs) can be filled with a wide range of inorganic materials, and thus can be used as ‘contrast agents’ if biologically absent elements are encapsulated. Here we show that sealed single-walled CNTs filled with lead, barium and even krypton can be produced, and externally decorated with peptides to provide affinity for sub-cellular targets. The agents are able to highlight specific organelles in multiplexed XRF mapping, and are, in principle, a general and versatile tool for this, and other modes of biological imaging

Mechanisms of relapse in acute leukaemia: involvement of p53 mutated subclones in disease progression in acute lymphoblastic leukaemia

Mutations of the p53 tumour suppressor gene are infrequent at presentation of both acute myeloblastic leukaemia (AML) and acute lymphoblastic leukaemia (ALL), being found in between 5–10% of AML and 2–3% of ALL. Here we have studied the frequency of detection of p53 mutations at relapse of both AML and B-precursor ALL. In those patients with detectable mutations at relapse we investigated whether the mutation was detectable at presentation and was thus an early initiating event or whether it had arisen as a late event associated with relapse. Bone marrow samples from 55 adults and children with relapsed AML (n = 41) or ALL (n = 14) were analysed for p53 gene alterations by direct sequencing of exons 5–9. For samples where a p53 mutation was found at relapse, analysis of presentation samples was carried out by direct sequencing of the exon involved, or by allele-specific polymerase chain reaction (PCR) if the mutation could not be detected using direct sequencing. A p53 mutated gene was found at relapse in seven out of 55 cases. The frequency was higher in relapsed ALL (four out of 14 cases; 28.6%) compared to AML (three out of 41 cases; 7.3%). In five out of the seven cases presentation samples were available to study for the presence of the mutation. In two out of two AML patients the p53 mutation was detectable in the presentation sample by direct sequencing. In three ALL patients analysis of presentation material by direct sequencing showed a small mutant peak in one case, the other two being negative despite the sample analysed containing > 90% blast cells. However in both of these patients, the presence of p53 mutation was confirmed in the presentation sample using allele-specific PCR. In one of these patients the emergence of a subclone at relapse was confirmed by clonality analysis using IgH fingerprinting. Our results confirm that in ALL p53 mutations are present in a proportion of patients at relapse. Furthermore cells carrying the mutation are detectable at presentation in a minor clone suggesting that p53 mutations in ALL may be a mechanism contributing to disease relapse. © 1999 Cancer Research Campaig