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This paper describes a procedure to measure the permeability P , diffusivity D, and rate of adsorption k 1 , thus determining the solubility S and rate of desorption k 2 of He, N 2 , O 2 , CH 4 , and CO 2 on a polydimethylsiloxane (PDMS) membrane. The described procedure is able to determine experimentally all the physical quantities that characterize the gas transport process through a thin rubber polymer membrane. The experiments were carried out at room temperature and at a transmembrane pressure of 1 atm. The results are in good agreement with the available data in the literature and offer an evaluation of k 1 and k 2 ., Competing Interests: The authors declare no conflict of interests

The purpose of this investigation is to fabricate PDMS membranes with reliable surface roughness in order to reduce the surface resistances and to study its impact on the permeation rate. The permeance of CO 2 through PDMS membranes with rough surfaces at nanoscale is studied and compared with the one of membranes with flat surfaces. At very low thickness, rough membranes have a permeance greater than that of membranes with flat surfaces. The enhancement occurs in a regime where the gas transport is sorption desorption surface rate limited, and cannot be explained by the increase in surface area due to the corrugation. The analysis, introducing a phenomenological model in analogy with electrical flow, indicates that nano-corrugation reduces the surface resistance. To test the model, the permeance of N 2 is also measured in the same experimental conditions and the influence of surface roughness on permeation rate of CO 2 , He, CH 4 and N 2 is studied. The comparison among the gases suggests that the Henry's coefficient depends on the surface roughness and allows discussing the role of roughness on membrane selectivity.

In the last decade the detection of the resistance of bacteria to antibiotics treatment, developed by different kind of bacteria, is becoming a huge problem. We hereby present a different approach to the current problem of detection of bacteria resistance to antibiotics. Our aims were to use the atomic force microscopy (AFM) to investigate bacteria morphological changes in response to antibiotics treatment and explore the possibility of reducing the time required to obtain information on their resistance. In particular, we studied Klebsiella pneumoniae bacteria provided by the Lavagna Hospital ASL4 Liguria (Italy), where there are cases linked with antibiotics resistance of the Klebsiella pneumoniae . By comparing AFM images of bacteria strains treated with different antibiotics is possible to identify unambiguously the Klebsiella pneumoniae strains resistant to antibiotics. In fact, the analysis of the AFM images of the antibiotic-sensitive bacteria shows clearly the presence of morphological alterations in the cell wall. While in the case of the antibiotic-resistant bacteria morphological alterations are not present. This approach is based on an easy and potentially rapid AFM analysis.

There is currently a growing interest in control of stretching of DNA inside nanoconfined regions due to the possibility to analyze and manipulate single biomolecules for applications such as DNA mapping and barcoding, which are based on stretching the DNA in a linear fashion. In the present work, we couple Finite Element Methods and Monte Carlo simulations in order to study the conformation of DNA molecules confined in nanofluidic channels with neutral and charged walls. We find that the electrostatic forces become more and more important when lowering the ionic strength of the solution. The influence of the nanochannel cross section geometry is also studied by evaluating the DNA elongation in square, rectangular, and triangular channels. We demonstrate that coupling electrostatically interacting walls with a triangular geometry is an efficient way to stretch DNA molecules at the scale of hundreds of nanometers. The paper reports experimental observations of λ-DNA molecules in poly(dimethylsiloxane) nanochannels filled with solutions of different ionic strength. The results are in good agreement with the theoretical predictions, confirming the crucial role of the electrostatic repulsion of the constraining walls on the molecule stretching.

We demonstrate the possibility of using a simple functionalization procedure, based on an initial vapour-phase silanization, to control the size and functionality of solid state nanopores. The presented results show that, by varying the silanization time, it is possible to modify the efficiency of probe molecule attachment, thus shrinking the pore to the chosen size, while introducing a specific sensing selectivity. The proposed method allows us to tune the nanopore biosensor adapting it to the specific final application, and it can be efficiently applied when the pore initial diameter does not exceed a limit dimension related to the mean free path of the silane molecules at the working pressure.

Several strategies have been developed for the control of DNA translocation in nanopores and nanochannels. However, the possibility to reduce the molecule speed is still challenging for applications in the field of single molecule analysis, such as ultra-rapid sequencing. This paper demonstrates the possibility to alter the DNA translocation process through an elastomeric nanochannel device by dynamically changing its cross section. More in detail, nanochannel deformation is induced by a macroscopic mechanical compression of the polymeric device. This nanochannel squeezing allows slowing down the DNA molecule passage inside it. This simple and low cost method is based on the exploitation of the elastomeric nature of the device, can be coupled with different sensing techniques, is applicable in many research fields, such as DNA detection and manipulation, and is promising for further development in sequencing technology.

Single molecule electrical sensing with nanopores is a rapidly developing field with potential revolutionary effects on bioanalytics and diagnostics. The recent success of this technology is in the simplicity of its working principle, which exploits the conductance modulations induced by the electrophoretic translocation of molecules through a nanometric channel. Initially proposed as fast and powerful tools for molecular stochastic sensing, nanopores find now application in a range of different domains, thanks to the possibility of finely tuning their surface properties, thus introducing artificial binding and recognition sites. Here we show the results of DNA translocation and hybridization experiments at the single molecule level by a novel class of selective biosensor devices that we call "DNA-Dressed NAnopore" (DNA(2)), based on solid state nanopore with large initial dimensions, resized and activated by functionalization with DNA molecules. The presented data demonstrate the ability of the DNA(2) to selectively detect complementary target sequences, that is to distinguish between molecules depending on their affinity to the functionalization. The DNA(2) can thus constitute the basis for the design of integrable parallel devices for mutation DNA analysis, diagnostics and bioanalytic investigations., (Copyright © 2011 Elsevier B.V. All rights reserved.)

We present the development and the electrical characterization of a polymeric nanochannel device. Standard microfabrication coupled to Focused Ion Beam (FIB) nanofabrication is used to fabricate a silicon master, which can be then replicated in a polymeric material by soft lithography. Such an elastomeric nanochannel device is used to study DNA translocation events during electrophoresis experiments. Our results demonstrate that an easy and low cost fabrication technique allows creation of a low noise device for single molecule analysis.

A Focused Ion Beam (FIB)-patterned silicon mould is used to fabricate elastomeric nanostructures, whose cross-section can be dynamically and reversibly tuned by applying a controlled mechanical stress. Direct-write, based on FIB milling, allows the fabrication of nanostructures with a variety of different geometries, aspect ratio, spacing and distribution offering a higher flexibility compared to other nanopatterning approaches. Moreover, a simple double replication process based on poly(dimethylsiloxane) permits a strong reduction of the fabrication costs that makes this approach well-suited for the production of low cost nanofluidic devices. DNA stretching and single molecule manipulation capabilities of these platforms have been successfully demonstrated., (This journal is © The Royal Society of Chemistry 2011)

We present data concerning the electrical properties of a class of biosensor devices based on bio-functionalized solid state nanopores able to detect different kinds of interactions between probe molecules, chemically attached to the pore surface, and target molecules present in solution and electrophoretically drawn through the nanometric channel. The great potentiality of this approach resides in the fact that the functionalization of a quite large pore (up to 50-60 nm) allows a sufficient diameter reduction for the attainment of a single molecule sensing dimension and selective activation, without the need for further material deposition, such as metal or oxides, or localized surface modification. The results indicate that it will be possible, in the near future, to conceive and design devices for parallel analysis of biological samples made of arrays of nanopores differently functionalized, fabricated by standard lithographic techniques, with important applications in the field of molecular diagnosis.

The possible use of nanopores for single DNA molecules biosensing has been demonstrated, but much remains to do in order to develop advanced engineered devices with enhanced stability, and controlled geometry and surface properties. Here we present morphological and electrical characterization of solid state silicon nitride nanopores fabricated by focused ion beam direct milling and chemically functionalized by probe oligonucleotides, with the final aim of developing a versatile tool for biosensing and gene expression profiling.

A quantitative surface reconstruction technique has been developed for the geometric characterization of three-dimensional structures by using a combined focused ion beam-scanning electron microscopy (FIB-SEM) instrument. A regular pattern of lines is milled at normal incidence on the sample to be characterized and an image is acquired at a large tilt angle. By analyzing the pattern under the tilted view, a quantitative estimation of surface heights is obtained. The technique has been applied to a test sample and nanoscale resolution has been achieved. The reported results are validated by a comparison with atomic force microscopy measurements.

In recent years there has been a rapid increase in nanotechnology applications to medicine in order to prevent and treat diseases in the human body. The established and future applications have the potential to dramatically change medical science. The present paper will give a few examples that could transform common medical procedures.

We report on the synthesis and characterization of elastomer colloidal AFM probes. Poly(dimethylsiloxane) microparticles, obtained by water emulsification and cross-linking of viscous prepolymers, are glued to AFM cantilevers and used for contact mechanics investigations on smooth substrates: in detail cyclic loading-unloading experiments are carried on ion-sputtered mica, the deformation rate and dwell time being separately controlled. We analyze load-penetration curves and pull-off forces with models due respectively to Zener; Maugis and Barquins; and Greenwood and Johnson and account for bulk creep, interfacial viscoelasticity, and structural rearrangements at the polymer-substrate interface. A good agreement is found between experiments and theory, with a straightforward estimation of colloidal probes' material parameters. We suggest the use of such probes for novel contact mechanics experiments involving fully reversible deformations at the submicrometer scale.