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Microcantilevers are increasingly being used to create sensitive sensors for rheology and mass sensing at the micro- and nano-scale. When operating in viscous liquids, the low quality factor of such resonant structures, translating to poor signal-to-noise ratio, is often manipulated by exploiting feedback strategies. However, the presence of feedback introduces poorly-understood dynamical behaviours that may severely degrade the sensor performance and reliability. In this paper, the dynamical behaviour of self-excited microcantilevers vibrating in viscous fluids is characterized experimentally and two complementary modelling approaches are proposed to explain and predict the behaviour of the closed-loop system. In particular, the delay introduced in the feedback loop is shown to cause surprising non-linear phenomena consisting of shifts and sudden-jumps of the oscillation frequency. The proposed dynamical models also suggest strategies for controlling such undesired phenomena.

The conversion of proteins into structured fibrillar aggregates is a central problem in protein chemistry, biotechnology, biology and medicine. It is generally accepted that aggregation takes place from partially structured states of proteins. However, the role of the residual structure present in such conformational states is not yet understood. In particular, it is not yet clear as to whether the α-helical structure represents a productive or counteracting structural element for protein aggregation. We have addressed this issue by studying the aggregation of pH-unfolded HypF-N. It has previously been shown that the two native α-helices of HypF-N retain a partial α-helical structure in the pH-unfolded state and that these regions are also involved in the formation of the cross-β structure of the aggregates. We have introduced mutations in such stretches of the sequence, with the aim of increasing the α-helical structure in the key regions of the pH-unfolded state, while minimizing the changes of other factors known to influence protein aggregation, such as hydrophobicity, β-Sheet propensity, etc. The resulting HypF-N mutants have higher contents of α-helical structure at the site(s) of mutation in their pH-unfolded states, but such an increase does not correlate with a change of aggregation rate. The results suggest that stabilisation of α-helical structure in amyloidogenic regions of the sequence of highly dynamic states does not have remarkable effects on the rate of protein aggregation from such conformational states. Comparison with other protein systems indicate that the effect of increasing α-helical propensity can vary if the stabilised helices are in non-amyloidogenic stretches of initially unstructured peptides (accelerating effect), in amyloidogenic stretches of initially unstructured peptides (no effect) or in amyloidogenic stretches of initially stable helices (decelerating effect)

An Open Source/Real-Time AFM Architecture to Perform Customizable Force Spectroscopy Experiments

The need for investigating the properties of new materials at nanoscale level continuously pushes the development of higher resolution measurement instruments. In this context, a promising dynamic atomic force microscopy setup, where the cantilever gets excited by a nonlinear feedback loop, has been recently introduced. In the first part of the paper the application of this working mode to imaging is experimentally investigated, showing the effectiveness of this novel approach. Furthermore, the presence of a variable saturation in the nonlinear loop is exploited to design a specific algorithm that dynamically adapts the cantilever free oscillation amplitude to sudden variations of the sample profile. In imaging applications this additional control action significantly reduces the tip-sample interaction force yet maintaining high image quality, thus resulting in a suitable setup for better preserving the state of soft and damageable samples such as biological specimens.

Riassunto. Sono più di dieci anni ormai che, con alterne vicende, “giochiamo” con il LEGO escogitando nuovi esperimenti per invogliare studenti d’ogni ordine e grado e semplici curiosi ad avvicinarsi alla scienza in modo divertente. Con il contributo del MIUR `e adesso disponibile un sito internet dedicato a questa attività di diffusione della cultura scientifica e tecnica attraverso il gioco. Abstract. More than ten years ago we started to “play” with LEGO to set up optical experiments for students of every age and amateur scientists. Since then, now and again, in spare time, we design new experiments. Now thanks to a financial support from MIUR a web site is available devoted to the diffusion of scientific and technical culture through ludic activity.

Natural variants of cerato-platanin (CP), a pathogen associated molecular pattern (PAMP) protein produced by Ceratocystis platani (the causal agent of the plane canker stain), have been found to be produced by other four species of the genus Ceratocystis, including five clones of Ceratocystis fimbriata isolated from different hosts. All these fungal strains were known to be pathogenic to plants with considerable importance in agriculture, forestry, and as ornamental plants. The putative premature proteins were deduced on the basis of the nucleotide sequence of genes orthologous to the cp gene of C. platani; the deduced premature proteins of Ceratocystis populicola and Ceratocystis variospora reduced the total identity of all the others from 87.3% to 60.3%. Cerato-populin (Pop1), the CP-orthologous protein produced by C. populicola, was purified and characterized. Pop1 was a well-structured ?/? protein with a different percentage of the ?-helix than CP, and it self-assembled in vitro in ordered aggregates. Moreover, Pop1 behaved as PAMP, since it stimulated poplar leaf tissues to activate defence responses able to reduce consistently the C. populicola growth.

Natural variants of cerato-platanin (CP), a pathogen associated molecular pattern (PAMP) protein produced by Ceratocystis platani (the causal agent of the plane canker stain), have been found to be produced by other four species of the genus Ceratocystis, including five clones of Ceratocystis fimbriata isolated from different hosts. All these fungal strains were known to be pathogenic to plants with considerable importance in agriculture, forestry, and as ornamental plants. The putative premature proteins were deduced on the basis of the nucleotide sequence of genes orthologous to the cp gene of C. platani; the deduced premature proteins of Ceratocystis populicola and Ceratocystis variospora reduced the total identity of all the others from 87.3% to 60.3%. Cerato-populin (Pop1), the CP-orthologous protein produced by C. populicola, was purified and characterized. Pop1 was a well-structured alfa/beta protein with a different percentage of the alfa-helix than CP, and it self-assembled in vitro in ordered aggregates. Moreover, Pop1 behaved as PAMP, since it stimulated poplar leaf tissues to activate defence responses able to reduce consistently the C. populicola growth.

We report on the fabrication and characterization of the first periodic sub-micron scale one- and two-dimensional surface structures in congruent 500 ?m thick lithium niobate crystal samples. Structures with periods from 2 ?m down to 500 nm, lateral feature sizes down to 200 nm and depths around 10 ?m, largely compatible with conventional waveguide fabrication, have been obtained. Such structures are fabricated by selective wet etching of ferroelectric domain engineered samples obtained by electric field poling performed at an overpoling regime. Holographic lithography is here used to obtain sub-micron periodic insulating gratings to be used for selective ferroelectric domain reversal. The short-pitch fabricated structures are attractive in a wide range of applications, such as nonlinear short-wavelength conversion processes, backward second-harmonic generation, fabrication of novel tunable photonic crystal (PC) devices, electro-optically modulated Bragg gratings. Moreover moire beating effect is used in the photolithographic process to fabricate even more complex structures which could find applications in complicated photonic bandgap devices involving for example micro-ring resonators. In order to investigate the possibility to utilize these structures for PC applications, accurate and complete topographic characterization has been performed by using different techniques. Atomic force microscope provides high-resolution information about the lateral and depth feature size of the structures. Interferometric techniques, based on digital holography, have been used for wide field information about the homogeneity and periodicity of the structures.