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A general single-step approach is introduced for the green fabrication of hybrid biosensors from water dispersion. The resulting device integrates the semiconducting properties of a carbon nanotube (CNT) and the functionality of a protein. In the initial aqueous phase, the protein (viz., lysozyme [LZ]) disperses the (6,5)CNT. Drop-casting of the dispersion on a test pattern (a silicon wafer with interdigitated Au source and drain electrodes) yields a fully operating, robust, electrolyte-gated transistor (EGT) in one step. The EGT response to biorecognition is then assessed using the LZ inhibitorN-acetyl glucosamine trisaccharide. Analysis of the output signal allows one to extract a protein-substrate binding constant in line with values reported for the free (without CNT) system. The methodology is robust, easy to optimize, redirectable toward different targets and sets the grounds for a new class of CNT-protein biosensors that overcome many limitations of the technology of fabrication of CNT biosensors

A novel approach to the preparation of ultraflat Ni substrates suitable to scanning probe microscopy imaging of immobilized polyhistidine-tagged proteins has been devised. Exploiting freshly cleaved mica, Ni thermal evaporation followed by thermal annealing in vacuum, and the template stripping method, we have obtained Ni substrates with a rms roughness as low as 0.12 nm, which bind readily polyhistidine-tagged proteins, enabling molecular resolution imaging of isolated molecules as well as of molecular submonolayers. Protein sample exposure to imidazole causes removal of the adsorbates, confirming the involvement of the polyhistidine tail in protein surface immobilization.

An integrated field-effect device for fully electronic deoxyribonucleic acid (DNA) detection was realized in a standard CMOS process. The device is composed of a floating-gate MOS transistor, a control-capacitor acting as integrated counterelectrode, and an exposed active area for DNA immobilization. The drain-current of the transistor is modulated by the electric charge carried by the DNA molecules. After DNA hybridization, this charge increases and a change in the output current is measured. Experimental results are provided. Full compatibility with a standard CMOS process-opens the way to the realization of low-cost large-scale integration of fast electronic DNA detectors.

The technique of electrochemical scanning tunneling microscopy (ECSTM) and spectroscopy (ECSTS) for studying electron transport through single redox molecules is here described. Redox molecules of both biological and organic nature have been studied by this technique with the aim of understanding the transport mechanisms ruling the flow of electrons via a single molecule placed in a nanometer-sized gap between two electrodes while elucidating the role of the redox density of states brought about by the molecule. The obtained results provide unique clues to single-molecule transport behavior and support the concept of single-molecule electrochemical gating.

Fundamental knowledge about the mechanisms of adhesion between oxide particles with diameters of few nanometers is impeded by the difficulties associated with direct measurements of contact forces at such a small size scale. Here we develop a strategy based on AFM force spectroscopy combined with all-atom molecular dynamics simulations to quantify and explain the nature of the contact forces between 10 nm small TiO(2) nanoparticles. The method is based on the statistical analysis of the force peaks measured in repeated approaching/retracting loops of an AFM cantilever into a film of nanoparticle agglomerates and relies on the in-situ imaging of the film stretching behavior in an AFM/TEM setup. Sliding and rolling events first lead to local rearrangements in the film structure when subjected to tensile load, prior to its final rupture caused by the reversible detaching of individual nanoparticles. The associated contact force of about 2.5 nN is in quantitative agreement with the results of molecular dynamics simulations of the particle-particle detachment. We reveal that the contact forces are dominated by the structure of water layers adsorbed on the particles' surfaces at ambient conditions. This leads to nonmonotonous force-displacement curves that can be explained only in part by classical capillary effects and highlights the importance of considering explicitly the molecular nature of the adsorbates.

The usual biophysical approach to the study of biological membranes is that of turning to model systems. From these models, general physical principles ruling the lateral membrane structure can be obtained. A promising model system is the supported lipid bilayer (SLB) which could foresee the simultaneous investigation of the structure and physical properties of lipid bilayers reconstituted with membrane proteins. A complete exploitation of the model system to retrieve biologically relevant information requires an in-depth knowledge of the possible effect that experimental parameters could have on the behavior of the SLB. Here we used atomic force microscopy (AFM) to study the effect of different types of substrates on the behavior of SLBs as far as their main phase transition is concerned. We found that different substrates (mica and silicon oxide) can affect in dissimilar ways the interleaflet coupling of the bilayer, which might represent a sort of lipid signaling allowing communication between receptors on the extracellular leaflet and cytoplasmic components. By decreasing the interaction between the SLB and the substrate the interleaflet coupling is preserved independently of the bilayer preparation strategy. Moreover, we investigated by time-lapse AFM an isothermal phase transition induced by a pH change on a SLB. We established that the presence of a pH gradient across the bilayer can weaken the strength of the interleaflet coupling which is present in symmetrical pH conditions.

Functional DNA scaffolds can be defined as DNA-based structures comprising chemical moieties facilitating and guiding the immobilization of additional nanocomponents. Due to the limited reactivity of DNA there is currently a need to develop rapid routes to expand its chemical repertoire and increase its versatility as a nanostructuring scaffold. We report a simple synthetic strategy for generating linear and stable double-stranded DNA scaffolds functionalized with multiple sites reactive towards free thiols, and the utility of this approach is demonstrated by immobilizing a model protein containing an accessible free thiol. This procedure is very versatile and could be easily expanded to other types of chemistries. This approach could also potentially be employed for the specific, oriented immobilization of various biomolecules and nanoparticles on predefined DNA architectures.

In this paper we are demonstrating an electrochemically driven self-assembling approach to achieve the space-resolved chemical functionalization of nanoelectrodes. After forming a self-assembled monolayer of electroactive quinones on a pair of nano-spaced (< 100 nm) electrodes, we enabled the binding of ssDNA exclusively on a single nanoelectrode by controlling the oxidation state at each modified electrode. This procedure attained the chemical differentiation of otherwise identical nanoelectrodes as the immobilized ssDNA retained its hybridization ability. Furthermore, we established that Kelvin probe force microscopy is a suitable space-resolved analytical technique for detecting this chemical functionalization at the nanoscale. The reported approach, enabling the space-selective patterning of (bio)molecules on nanoelectrode surfaces, can find application in complex nanosensor structure and molecular electronics implementations.

In this paper, we report the metallization of a dsDNA template using a novel photography-derived two-step strategy in which dsDNA is first complexed with Ag(I) ions and then irradiated with UV light at 254 nm. The nucleobases act as light harvesters and sensitizers, triggering the photoreduction of the complexed silver ions. This process yields a silver nanoparticles blueprint along the DNA strand. The silver latent image is then developed by depositing metallic nickel through an electroless plating process. This photography-derived procedure generates very homogeneous and evenly distributed strings of silver-core/nickel-shell nanoparticles. Although still discontinuous, we believe that such chains can serve as the base for obtaining continuous metal nanowires. Furthermore, this process can most likely be extended to other plating metals, resulting in a broadly general procedure for metallizing DNA with a variety of different materials. Because of the intrinsic simplicity in using light as the key step, this methodology might be amenable to large-scale development, eventually leading to a very efficient molecular-photolithography process.

A novel solid-state biosensor for label-free detection of DNA hybridization is presented. The new device is realized in a standard CMOS process, thus allowing the realization of low-cost, portable, fully integrated devices. The detection mechanism is based on the field-effect of the intrinsic negative electric charge of DNA molecules which modulates the threshold voltage of a floating-gate MOS transistor. A fluid cell was developed for delivering DNA samples on the active surface of the chip. The device has an integrated, individual counter-electrode, so dry measurements are possible increasing lifetime of the chip and speeding up the experiment. Successful measurements on a first prototype of the chip, hosting 16 sensors individually addressable, are provided as proof of concept. (c) 2006 Elsevier B.V. All rights reserved.

Maps of the electric field distribution on the surface of thick film resistors (TFRs) have been acquired by using electric force microscopy (EFM). TFRs based on various types of conducting phases (Bi-ruthenate, Pb-ruthenate, or RuO2) and with different volume fractions in the glassy matrix have been examined. Scanning electron microscopy, x-ray energy dispersive spectroscopy and x-ray diffraction have been used to correlate the EFM results to the morphological, microchemical, and structural characteristics of the samples. The evolution of the TFRs microstructure and the segregation characteristic with the firing conditions have been investigated. The results showed that the concentration of the electric field around the conductive grains is a general feature of all the films, independently of the resistor composition, and a meander-like path of charge carriers on a microscopic scale has been assessed. The observations also indicated that at high firing temperatures the segregated structure did not disappe...

Gas absorbing materials (getters) find several applications in modern vacuum technology; in particular to maintain required vacuum levels in evacuated and sealed enclosures. The gas absorbing properties of these getters depend on the physico-chemical nature of their surfaces. The aim of this work is to study the absorption properties of commercial Zr-based alloys (non-evaporable getters) after mechanical alloying by means of a high vacuum planetary ball milling equipped with an in-situ compaction facility. The main aim was to refine the grain size and to develop particular defect structures to enhance the getter properties. The results have shown an improvement of the specific pumping speed of the ball milled commercial Zr-Zr(V,Fe)2 alloy with respect to the starting microcrystalline material. In particular, under our experimental conditions, the specific pumping speed vs absorbed gas curve presents a maximum after 2 hours of milling; prolonged milling reduced the pumping speed of the alloyed material. This behaviour is explained in terms of two opposing simultaneous chemical and structural effects.

Elastic fibers of beef ligamentum nuchae were observed by atomic force microscopy and data compared with those obtained by conventional and freeze-fracture electron microscopy. Fresh isolated elastin fibers as well as thin sections of ligament fragments, which were fixed and embedded either in relaxed or in stretched conditions, were analysed. The results confirm that, at least in beef ligamentum nuchae, elastic fibers consist of beaded filaments which can be oriented by stretching in the direction of the force applied. Moreover, atomic force microscopy revealed that these beaded filaments are laterally connected by periodical bridges which become more pronounced upon stretching. The data clearly show that elastin molecules are organized in a rather ordered array, at least at the super-molecular level, and a depiction of the elastin organization in beef ligamentum nuchae is attempted.

Native, unfixed collagen fibrils from rat tail tendon were dehydrated following different procedures and observed under a FEG-SEM and an AFM operated in Tapping Mode (TMAFM). Freeze-etched, untreated fibrils from the same tissue were also observed for comparison. The most notable features of the fibril surface, i.e., the gap/overlap alternation and three prominent intraperiod ridges, were simultaneously visible only in freeze-etched specimens, while under the SEM and the TMAFM their appearance was dependent on both the dehydration procedure and the visualization technique. The different susceptibility of the collagen fibril surface structures to various treatments clearly implies the existence of domains of different composition. Moreover, identical specimens were imaged differently by SEM and TMAFM, highlighting instrument-specific advantages and limitations. The onset of dehydration-dependent, procedure-specific artifacts should be considered in high-resolution studies of connective tissues. As for any biological specimen, the final aspect of collagen fibrils is determined no less by the preliminary treatments than by the visualization approach.

The fabrication and performances of cantilevered probes with reduced parasitic capacitance starting from a commercial Si3N4 cantilever chip is presented. Nanomachining and metal deposition induced by focused ion beam techniques were employed in order to modify the original insulating pyramidal tip and insert a conducting metallic tip. Two parallel metallic electrodes deposited on the original cantilever arms are employed for tip biasing and as ground plane in order to minimize the electrostatic force due to the capacitive interaction between cantilever and sample surface. Excitation spectra and force-to-distance characterization are shown with different electrode configurations. Applications of this scheme in electrostatic force microscopy, Kelvin probe microscopy and local anodic oxidation is discussed., 4 pages and 3 figures. Submitted to Applied Physics Letters