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One of the major bottlenecks of the traditional Current Transformer Energy Harvester (CTEH) is the instable output induced by the wide-range variations of the current in transmission lines. In this work, a novel CTEH capable of generating a stable output is demonstrated by using a core fabricated with saturable magnetic material. The stable output of the CTEH is enabled by the constant voltage-time product in its saturable characteristic. The proposed CTEH is implemented with a resistive load representing the load of electronic devices. When the current in the primary side of the CTEH’s increases from 1A to 1000A, the maximum power on the load can reach about 0.5W, demonstrating the feasibility of using the CTEH with the saturable magnetic core as a quasi-stable power supply.

Phononic materials are artificial composites with unprecedented abilities to control acoustic waves in solids. Their performance is mainly governed by their architecture, determining frequency ranges in which wave propagation is inhibited. However, the dynamics of phononic materials also depends on the mechanical and material properties of their constituents. In the case of viscoelastic constituents, such as most polymers, it is challenging to correctly predict the actual dynamic behavior of real phononic structures. Existing studies on this topic either lack experimental evidence or are limited to specific materials and architectures in restricted frequency ranges. A general framework is developed and employed to characterize the dynamics of polymer phononic materials with different architectures made of both thermoset and thermoplastic polymers, presenting qualitatively different viscoelastic behaviors. Through a comparison of experimental results with numerical predictions, the reliability of commonly used elastic and viscoelastic material models is evaluated in broad frequency ranges. Correlations between viscous effects and the two main band-gap formation mechanisms in phononic materials are revealed, and experimentally verified guidelines on how to correctly predict their dissipative response are proposed in a computationally efficient way. Overall, this work provides comprehensive guidelines for the extension of phononics modeling to applications involving dissipative viscoelastic materials.

Suspended microchannel resonators (SMRs) are sensitive biosensors for microgravimetric analysis. In this work, an innovative glass SMR was monolithically manufactured by a femtosecond laser technique coupled with a wet etching. The SMR was used to analyze liquids with different density, thanks to a 1.04·10−3 kg/m3 density resolution, comparable with the state-of-art silicon-based SMRs. The effective biosensing capability was demonstrated by evaluating the microbial load of different concentrations of P. fluorescens. This innovative and completely transparent SMR can be exploited for real time biosensing, associated with a microscope analysis. Rapid and cost-effective 3D FEMTOPRINT technology can sustain industrial production for point-of-care devices.

The extreme miniaturization in NEMS resonators offers the possibility to reach an unprecedented resolution in high-performance mass sensing. These very low limits of detection are related to the combination of two factors: a small resonator mass and a high quality factor. The main drawback of NEMS is represented by the highly complex, multi-steps, and expensive fabrication processes. Several alternatives fabrication processes have been exploited, but they are still limited to MEMS range and very low-quality factor. Here we report the fabrication of rigid NEMS resonators with high-quality factors by a 3D printing approach. After a thermal step, we reach complex geometry printed devices composed of ceramic structures with high Young’s modulus and low damping showing performances in line with silicon-based NEMS resonators ones. We demonstrate the possibility of rapid fabrication of NEMS devices that present an effective alternative to semiconducting resonators as highly sensitive mass and force sensors., NEMS devices, nano-electro-mechanical systems, by virtue of their minute size, offer ultra-high sensitivity, though at the expense of manufacturing complexity. Here, Stassi et al succeed in manufacturing high quality factor NEMS devices using high resolution 3D printing.

Fano resonance refers to an interference between localized and continuum states that was firstly reported for atomic physics and solid-state quantum devices. In recent years, Fano interference gained more and more attention for its importance in metamaterials, nanoscale photonic devices, plasmonic nanoclusters and surface-enhanced Raman scattering (SERS). Despite such interest in nano-optics, no experimental evidence of Fano interference was reported up to now for purely nanomechanical resonators, even if classical mechanical analogies were referred from a theoretical point of view. Here we demonstrate for the first time that harmonic nanomechanical resonators with relatively high quality factors, such as cantilevers vibrating in vacuum, can show characteristic Fano asymmetric curves when coupled in arrays. The reported findings open new perspectives in fundamental aspects of classical nanomechanical resonators and pave the way to a new generation of chemical and biological nanoresonator sensors with higher parallelization capability.

Resistive switching (RS) devices based on self-assembled nanowires (NWs) and nanorods (NRs) represent a fascinating alternative to conventional devices with thin film structure. The high surface-to-volume ratio may indeed provide the possibility of modulating their functionalities through surface effects. However, devices based on NWs usually suffer from low resistive switching performances in terms of operating voltages, endurance and retention capabilities. In this work, we report on the resistive switching behaviour of ZnO NW arrays, grown by hydrothermal synthesis, that exhibit stable, bipolar resistive switching characterized by SET/RESET voltages lower than 3 V, endurance higher than 1100 cycles and resistance state retention of more than 105 s. The physical mechanism underlying these RS performances can be ascribed to nanoionic processes involving the formation/rupture of conductive paths assisted by oxygen-related species in the ZnO active layer. The reported results represent, to the best of our knowledge, the best resistive switching performances observed in ZnO NW arrays in terms of endurance and retention.

Microcantilever-based biosensors have shown the ability of highly sensitive label-free detection by allowing the transduction of a target mass into a resonant frequency shift. Even if they have been widely adopted in the last years as high sensitive mass detectors, precision and specificity of such tools are often inadequate. A new platform able to precisely characterize in dynamic mode several of these micromechanical resonators is here presented. Consequently, to the examination of the main parameters involved in a measurement, repeatability and reproducibility of the automated cantilever-based system were estimated. The reported analyses demonstrated that the uncertainty of the system could be reduced to a standard deviation of 6.5 × 10 -6 (parts per million). Thanks to its fine precision, the here-proposed sensing platform was able to detect aflatoxins in naturally contaminated nuts at concentrations as low as 40 pg/mL, nearly two orders of magnitude more sensitive than previous attempts reported in the literature with similar devices.

Suspended nanochannel resonators (SNRs) are promising devices able to characterize mass down to the attogram scale, thus being able to detect nanoparticles or biomolecules. In this paper, we present a flexible fabrication process for SNRs based on a sacrificial layer approach that allows to easily tailor the dimensions of the nanochannel by changing the thickness of the sacrificial layer or its patterning during the lithographic step. The resonance properties of the fabricated SNR are investigated in terms of resonance frequency and frequency stability (Allan deviation). Liquids of different densities are injected in the device and, from the shift of the resonance peaks, the mass responsivity of the resonators is assessed to be up to 3.90 mHz/ag. To the best of our knowledge, the devices here presented are the first example of suspended nanochannel resonators with a channel height as low as 50 nm fabricated with a top-down approach.

Self-standing and flexible membranes based on reduced graphene oxide (rGO)/SnO2 nanocomposite and cellulose fibers are here presented. The flexible membranes are prepared through an easy and eco-friendly protocol: the rGO/SnO2 nanocomposite is synthetized via a microwave-assisted procedure and then assembled with microfibrillated cellulose (MFC) through a water-based process. This process leads to the formation of a nanocomposite in which cellulose nanofibers are integrated with the graphene matrix. Beyond the good flexibility, the nanocomposite membranes present interesting properties in terms of capacitive behavior and catalytic activity: the electrochemical characterizations revealed that such material is an extremely competitive candidate for the oxygen reduction reaction, even comparable to the commonly used Pt-based catalysts. Furthermore, the possible application as electrodes for flexible supercapacitors and piezoresistive sensors is also investigated showing the great potential of such composite material.

Suspended microchannel resonators (SMRs) have been recently developed as highly sensitive platforms to study bacteria, cell populations, antibiotic resistance and other micron-sized analytes. Unfortunately, the time-consuming and challenging fabrication process represents the main drawback for the implementation of these platforms as new point-of-care devices. In this work, we show that femtosecond laser direct writing can be successfully implemented as a rapid and cost-effective 3D fabrication process able to define the suspended resonant structure and the embedded microfluidic channel in one-step, only. Furthermore, the use of a fused silica substrate guarantees a totally transparent resonator, a useful property in view of adding optical analyses to the mechanical one. The resonance properties of the fabricated SMRs were accurately characterized in terms of frequency, quality factor and Allan deviation, in different working conditions. The monolithic glass SMR is able to analyze with high precision liquids with different mass density, thanks to a density resolution (1.04·10−3 kg/m3) that is the highest among SMRs and microcapillaries used for this purpose. Finally, the effective biosensing capability is demonstrated by evaluating the microbial load of aqueous solutions containing different concentrations of P. fluorescens.

Laser-induced graphene (LIG) emerged as one of the most promising materials for flexible functional devices. However, the attempts to obtain LIG onto elastomeric substrates never succeed, hindering its full exploitation for stretchable electronics. Herein, a novel polymeric composite is reported as a starting material for the fabrication of graphene-based electrodes by direct laser writing. A polyimide (PI) powder is dispersed into the poly(dimethylsiloxane) (PDMS) matrix to achieve an easily processable and functional elastomeric substrate, allowing the conversion of the polymeric surface into laser-induced graphene (LIG). The mechanical and electrical properties of the proposed material can be easily tuned by acting on the polyimide powder concentration. The reported procedure takes advantage from the simple casting process, typical of silicone elastomer, allowing to produce electrodes conformable to any kind of shape and surface as well as complex three-dimensional structures. Electrochemical capacitors and strain gauges are selected as flexible prototypes to demonstrate the multifunctional properties of the obtained LIG on the PDMS/PI composite substrate.

Nanomechanical mass spectrometry is a recent technological breakthrough that enables the real-time analysis of single molecules. In contraposition to its extreme mass sensitivity is a limited capture cross-section that can hinder measurements in a practical setting. Here we show that weak-coupling between devices in resonator arrays can be used in nanomechanical mass spectrometry to parallelize the measurement. This coupling gives rise to asymmetric amplitude peaks in the vibrational response of a single nanomechanical resonator of the array, which coincide with the natural frequencies of all other resonators in the same array. A rigorous theoretical model is derived that explains the physical mechanisms and describes the practical features of this parallelization. We demonstrate the significance of this parallelization through inertial imaging of analytes adsorbed to all resonators of an array, with the possibility of simultaneously detecting resonators placed at distances a hundred times larger than their own physical size., Designing large-scale parallelization of nanomechanical array measurements remains elusive. Here, the authors propose weak-coupling between similar devices to evaluate the resonance frequencies of a whole resonator array with a single measurement.

ZnO nanomaterials are gaining lots of attention due to their biocompatible nature coupled with promising piezoelectric properties, envisioning a new generation of lead-free smart materials. Herein, an effective strategy to improve the piezoelectric behaviour of sputtered ZnO thin films is proposed by introducing a nanobranched porous thin film structure composed by a network of randomly-oriented wurtzite crystallites, rather than using compact ZnO thin films, considered in this work as a conventional reference for sputtered ZnO thin film structures. The nanobranched ZnO structure shows a hydrophilic behavior together with a piezoelectric output voltage of around 3 V. In comparison, compact ZnO thin films exhibit a maximum piezoelectric voltage generation below 0.8 V and a hydrophobic state. The more defective structure of the nanobranched ZnO thin films, with respect of the long-range ordered crystal structure of compact ZnO thin films, reduces free carrier concentration and mobility, thus limiting the screening potential and at the same time improving piezoelectric voltage generation. All the characterization results highlight the promising perspectives in using nanobranched ZnO thin films as novel piezoelectric materials for biosensing and tissue engineering applications, as well as for lead-free piezoelectric sensors and energy harvesting systems.

In this work flexible composite nanogenerators were prepared aiming to identify and optimize the exploitation of the piezoelectric effect in mechanical energy harvesting. A novel shape-controlled synthesis of ZnO microstructures through hydrothermal route was achieved resulting in different morphologies and aspect-ratio particles, microwires, multipods, and desert-roses. The three different microparticles and round-shaped commercial nanoparticles were incorporated into a polydimethylsiloxane matrix and a comparative study on the piezoelectric output power dependence on the filler morphology was carried out. The highest performances, i.e. output voltage of 10 V and a maximum power of 55 µW, were obtained with the highest aspect-ratio ZnO filler, the microwires, dispersed in the PDMS matrix at a 40 wt% concentration. Considering the generated voltage dependence on the size and aspect-ratio of the fillers, a working mechanism was formulated. The nanogenerators were then exploited to charge a homemade carbon-based supercapacitor. The voltage charging curves confirm the voltage generation trend based on the high aspect-ratio particles, showing that the best performances are obtained by the microwires-based composite nanogenerator. This work thus contributes to clarify the piezoelectric mechanism in composite nanogenerators and to maximize the output power generation in view of self-powered nanodevices able to recover and store waste environmental energy.

The thermally-induced crystallization of anodically grown TiO2 amorphous nanotubes has been studied so far under ambient pressure conditions by techniques such as differential scanning calorimetry and in situ X-ray diffraction, then looking at the overall response of several thousands of nanotubes in a carpet arrangement. Here we report a study of this phenomenon based on an in situ transmission electron microscopy approach that uses a twofold strategy. First, a group of some tens of TiO2 amorphous nanotubes was heated looking at their electron diffraction pattern change versus temperature, in order to determine both the initial temperature of crystallization and the corresponding crystalline phases. Second, the experiment was repeated on groups of few nanotubes, imaging their structural evolution in the direct space by spherical aberration-corrected high resolution transmission electron microscopy. These studies showed that, differently from what happens under ambient pressure conditions, under the microscope’s high vacuum (p < 10−5 Pa) the crystallization of TiO2 amorphous nanotubes starts from local small seeds of rutile and brookite, which then grow up with the increasing temperature. Besides, the crystallization started at different temperatures, namely 450 and 380 °C, when the in situ heating was performed irradiating the sample with electron beam energy of 120 or 300 keV, respectively. This difference is due to atomic knock-on effects induced by the electron beam with diverse energy.

Herein a complete characterization of single TiO2 nanotube resonator was reported for the first time. The modal vibration response analysis allows a non-invasive indirect evaluation of the mechanical properties of the TiO2 nanotube. The effect of post-grown thermal treatments on nanotube mechanical properties was investigated and carefully correlated to the chemico-physical parameters evolution. The Young's modulus of TiO2 nanotube rises linearly from 57 GPa up to 105 GPa for annealing at 600 °C depending on the compositional and crystallographic evolution of the nanostructure. Considering the growing interest in single nanostructure devices, the reported findings allow a deeper understanding of the properties of individual titanium dioxide nanotubes extrapolated from their standard arrayed architecture.

The thermally-induced crystallization of anodically grown TiO2 amorphous nanotubes has been studied so far under ambient pressure conditions by techniques such as differential scanning calorimetry and in situ X-ray diffraction, then looking at the overall response of several thousands of nanotubes in a carpet arrangement. Here we report a study of this phenomenon based on an in situ transmission electron microscopy approach that uses a twofold strategy. First, a group of some tens of TiO2 amorphous nanotubes was heated looking at their electron diffraction pattern change versus temperature, in order to determine both the initial temperature of crystallization and the corresponding crystalline phases. Second, the experiment was repeated on groups of few nanotubes, imaging their structural evolution in the direct space by spherical aberration-corrected high resolution transmission electron microscopy. These studies showed that, differently from what happens under ambient pressure conditions, under the microscope’s high vacuum (p < 10−5 Pa) the crystallization of TiO2 amorphous nanotubes starts from local small seeds of rutile and brookite, which then grow up with the increasing temperature. Besides, the crystallization started at different temperatures, namely 450 and 380 °C, when the in situ heating was performed irradiating the sample with electron beam energy of 120 or 300 keV, respectively. This difference is due to atomic knock-on effects induced by the electron beam with diverse energy.

Zinc oxide nanorods (ZnO NRs) were grown in water solution on different conductive substrates. In particular, several metal layers, such as Cu, Ni, Pt, Ag, Au, deposited on silicon substrates, and F-doped SnO2 (FTO) coated-glass wafers were investigated as bottom electrodes and their influence on the properties of the synthesized ZnO nanorods were studied. The samples were characterized by scanning electron microscopy, X-ray diffraction, atomic force microscopy, current – voltage (I – V) and photoluminescence measurements. We obtained vertically aligned ZnO nanorod arrays on all the considered substrates, proving how ease and reproducible is the hydrothermal growth of ZnO nanorods on different conductive layers. We here show how the morphology and the optical and electrical features of the array depend on the conductive material deposited as bottom layer.

Silver particles with spiky nanostructured morphologies have been obtained by two different wet-synthesis approaches. A detailed investigation was carried out into the synthesis parameters to tune the shape of the sample into desert-rose- and succulent-like particles. The first synthetic route was based on the reduction of silver nitrate by iron sulfate in the presence of maleic acid as anisotropic agent, whereas in the second method ascorbic acid was used as the reducing agent and citric acid as the anisotropic agent. A nucleation model is proposed to explain the growth mechanism and the effect of each parameter on the particle morphology. These Ag nanostructured spiky particles have been used as conductive fillers in polymeric piezoresistive composites, the working principle of which is based on the tunneling conduction mechanism. Composite samples were thus prepared and characterized, demonstrating the enhancing effect of the sharp protrusions on the tunneling phenomena upon a mechanical compressive strain.

Graphical abstractDisplay Omitted The optimised fabrication process for a PZT actuated microswitch was developed.A comparison between standard ad optimised process was carried out.The actuation properties of the device were evaluated.The optimised process improves the piezoelectric response.Actuating the device a resistance switch from 1k? to 2? was observed. In this work the fabrication of a piezoelectrically actuated microswitch for high current applications is proposed. The device was obtained by assembling two silicon substrates: one containing the signal lines and the other enclosing a silicon nitride (Si3N4) microcantilever. This latter operates as a switch by closing the circuit with a metal electrode on its tip. A layer of lead zirconate titanate (PZT), deposited by sol-gel method, constitutes the actuation element of the microcantilever. The bottom and top electrodes of the PZT were respectively made of thin Ta/Pt and Au layers while the signal lines and the contact electrode on the microcantilever tip were made of Ti/Al. A comparison between microcantilevers characterised by different bottom electrodes is presented: (i) Ta/Pt deposited at 300?C and patterned by wet etching, (ii) Ta/Pt deposited at 100?C and patterned by lift-off. The microcantilevers fabricated with the latter metallisation show a considerable symmetry of the piezoelectric response and a wide microcantilever displacement. Thus, in this device the cantilever microstructures are able to close the gap between the signal lines with a resulting contact resistance of about 2?.

The feedback in the motor relearning therapy is essential and helpful for hemiplegic patient training. Tracking plantar pressure is clinically imperative to evaluate the foot function and in particular to assist patients with musculoskeletal and neurological diseases in the development of normal gait functionality. A flexible piezoresistive insole with dedicated electronics was developed to measure both the pressure distribution under 64 nodes arranged in the main plantar regions and the mean plantar pressure during walking activity with a sampling frequency of 20 Hz. This study reports on the easy and cost effective approach used to fabricate the flexible insole based on a piezoresistive material composed by copper spiky microparticles dispersed into silicon rubber. The entire insole was fabricated by single step casting technique, and then completed with a patterned metalized polyimide films as bottom electrode, while the top electrode was directly sputtered on the sample.

We present a robust and flexible tactile sensor based on piezoresistive sensing material, constituted by a polymeric composite with nanostructured spiky particles as filler. The composite is able to exploit tunneling conduction mechanism when subjected to a compressive load. We have here integrated this quantum tunneling composite (QTC) with an ad-hoc electronic read-out circuit. In addition a software interface can monitor and visualize the applied mechanical pressure, thus leading to a complete tactile sensor device. Concerning the sensing material, the piezoresistive composite shows an enhanced tunneling conduction due to the presence of nickel particles with nanostructured sharp tips embedded in a silicone matrix. We registered an increase up to nine orders of magnitude of the composite electrical conduction in response to a mechanical strain. The sensor consisted in a continuous layer of functional composite sandwiched between a matrix of patterned top and bottom electrodes. The planar sensor can thus be modeled as a two-dimensional array of resistors whose value decreases by increasing the applied pressure. We also designed an ad-hoc electronic read-out circuit, able to read and process the resistance variations of the sensor upon a compressive load, thus providing not only the pressure intensity but also the pressure distribution data. A software interface was able to achieve the real-time tridimensional response and lead to the visualization of the compressed regions on the sensor. The present device is an efficient and low-cost prototype of tactile sensing skin, thus readily enabling its use for human robotic applications.

Nanostructured polymeric composites are promising materials for the fabrication of piezoresistive devices because they show a huge variation in electrical resistance when subjected to mechanical deformation. Quantum tunneling composites feature a conduction mechanism occurring between the metallic filler and copper particles embedded in a polydimethylsiloxane (PDMS) insulating matrix, and the mechanism is enhanced by the spiky morphology of the particles. PEDOT:PSS electrodes are patterned on either side of the composite by inkjet printing, a technology that allows one-step fabrication processes. The adhesion and spreading of conductive printed ink drops are controlled and enhanced by pre-treating the samples surface in an atmospheric pressure plasma customized system. Because of an extremely high metal to polymer ratio, which results in the different surface and dielectric properties of the composite, conventional plasma conditions are not suitable to allow the control of spreading. The optimal plasma conditions for ink/surface compatibility were found using quantitative comparison based on image analysis and numerical interpretation of the adhesion/roughness properties such as bulging and spread.

The dimensional confinement and oriented crystallization are both key factors in determining the piezoelectric properties of a polymeric nanostructured material. Here we prepare arrays of one-dimensional polymeric nanowires showing piezoelectric features by template-wetting two distinct polymers into anodic porous alumina (APA) membranes. In particular, poly(vinylidene fluoride), PVDF, and its copolymer poly(vinylidene fluoride-trifluoroethylene), PVTF, are obtained in commercially available APA, showing a final diameter of about 200 nm and several micrometers in length, reflecting the templating matrix features. We show that the crystallization of both polymers into a ferroelectric phase is directed by the nanotemplate confinement. Interestingly, the PVDF nanowires mainly crystallize into the β-phase in the nanoporous matrix, whereas the reference thin film of PVDF crystallizes in the α nonpolar phase. In the case of the PVTF nanowires, needle-like crystals oriented perpendicularly to the APA channel walls are observed, giving insight on the molecular orientation of the polymer within the nanowire structure. A remarkable piezoelectric behavior of both 1-D polymeric nanowires is observed, upon recording ferroelectric polarization, hysteresis, and displacement loops. In particular, an outstanding piezoelectric effect is observed for the PVDF nanowires with respect to the polymeric thin film, considering that no poling was carried out. Current versus voltage (I-V) characteristics showed a consistent switching behavior of the ferroelectric polar domains, thus revealing the importance of the confined and oriented crystallization of the polymer in monodimensional nanoarchitectures.

This paper deals with the preparation and characterization of nanocomposite (NC) materials, comparing different technologies for sample fabrication, in view of their possible application as piezoelectric sensors. Those NCs consist on BaTiO3 nanoparticles embedded into a polyvinylidene fluoride matrix, where both the ceramic and the polymeric phases could exhibit ferroelectricity. In particular, we compare the properties of samples prepared through three different methods, i.e., solvent casting, enabling a fast realization, spin-coating, which allows to realize thin flexible films particularly interesting for large area sensors, and hot embossing, which is exploited to modify the residual porosity in the thick films. The influence of the fabrication techniques on the physical and chemical properties is investigated. Different electrode materials have been tested and compared, ranging from sputtered Pt to an engineered thermally evaporated Ti/Au bilayer. Leakage current, polarization, displacement curves, and piezoelectric coefficient d 33 are evaluated by small signal indirect measurements, comparing the properties of different materials and understanding how processing technologies influence the sensor performances by acting on the functional materials.

In this paper, we report on the effect of micro- and nano-structuration on the piezoelectric properties of polymeric samples. We prepare micro-sized pillars and nano-wires (thus 1-D structures) of a piezoelectric polymer Poly(VinyliDene Fluoride-Tri FluoroEthylene) PVDF-TrFE and we compare their structural and piezoelectrical properties with a thin film (thus 2-D) of the same material. X-ray diffraction and infrared spectroscopy measurements show that the crystallization of the polymer into the ferroelectric $\beta$ -phase is affected by the size of the confinement. The direct and converse piezoelectric characterization of the three polymeric structures shows important improvements as far as the nano-structuration is reached. As a proof of concept, we demonstrate the use of the three polymeric structures as potential flexible tactile sensors and bendable energy harvesters, showing a profound effect of the micro- and nano-structuration on the device performances.

Zinc Oxide (ZnO) nanostructures represent promising substrate materials for numerous applications, ranging from new generation solar cells, to bio- and chemical sensors. This interest is due to particular physical and chemical properties and highly active surface areas. Despite showing promising perspectives, the performances of ZnO nanomaterials are affected by several drawbacks, including a poor chemical stability against reaction solutions and intrinsic defects that are still preventing their integration into product applications. To overcome some of these limitations, different functionalization strategies have been introduced to engineer the ZnO surface properties. The synthetic methods used for surface functionalization are here discussed and analyzed with respect to the morphology of the agent to be anchored and to the functionalization approach. These approaches range from continuous coatings, to low-dimensional ligands like nanoparticles, photosensible dyes, quantum dots and organic compounds.

New photo-curable polymers for 3D printing are provided, exhibiting mechanical light-responsivity upon laser irradiation. Azobenzene moieties are employed both as dyes in the 3D printing process and as active groups providing the desired light responsivity. The incorporation of azobenzene units into polymeric matrices allows a reversible and controllable change of the Young's modulus of a crosslinked micrometric structure. Depending on the temperature of operation, laser irradiation induces either a decrease (photo-softening) or an increase (photo-hardening) of the Young's modulus. Such a behaviour can be spatially controlled in order to locally modify the mechanical features of 3D printed objects such as microcantilevers.

In this study, we show for the first time the production of mass-sensitive polymeric biosensors by 3D printing technology with intrinsic functionalities. We also demonstrate the feasibility of mass-sensitive biosensors in the form of microcantilever in a one-step printing process, using acrylic acid as functional comonomer for introducing a controlled amount of functional groups that can covalently immobilize the biomolecules onto the polymer. The effectiveness of the application of 3D printed microcantilevers as biosensors is then demonstrated with their implementation in a standard immunoassay protocol. This study shows how 3D microfabrication techniques, material characterization, and biosensor development could be combined to obtain an engineered polymeric microcantilever with intrinsic functionalities. The possibility of tuning the composition of the starting photocurable resin with the addition of functional agents, and consequently controlling the functionalities of the 3D printed devices, paves the way to a new class of mass-sensing microelectromechanical system devices with intrinsic properties.

The incidence of allergic disease is globally increasing so much that food allergy is actually considered as one of the main diseases of civilization, as well as among the major costs for healthcare worldwide. In such a scenario, the recent legislations introduced from European Union to protect consumers drastically drive the need for rapid, sensitive, and robust techniques to detect allergens within foodstuffs. We here report on an innovative immunorecognition method for β-lactoglobulin milk allergen detection, based on microcantilever resonator arrays, a promising class of biosensors. An original sandwich assay that uses the same polyclonal antibody as capture and secondary immunorecognition agent was proposed to overcome the low affinity of the simple direct method. The developed immunoassay showed better Limit Of Detection (LOD) and Limit Of Quantification (LOQ) than commercial ELISA plates, even after an aging of four months. To our knowledge, this work represents the first example in the literature of successfully immunodetection of milk allergens in low concentrations by microcantilever resonator arrays, thus opening new perspectives on alternative diagnostic tools for milk allergens screening tests.

An efficient way to increase the binding capability of microcantilever biosensors is here demonstrated by growing zinc oxide nanowires (ZnO NWs) on their active surface. A comprehensive evaluation of the chemical compatibility of ZnO NWs brought to the definition of an innovative functionalization method able to guarantee the proper immobilization of biomolecules on the nanostructured surface. A noteworthy higher amount of grafted molecules was evidenced with colorimetric assays on ZnO NWs-coated devices, in comparison with functionalized and activated silicon flat samples. ZnO NWs grown on silicon microcantilever arrays and activated with the proposed immobilization strategy enhanced the sensor binding capability (and thus the dynamic range) of nearly 1 order of magnitude, with respect to the commonly employed flat functionalized silicon devices. Graphical Abstract An efficient way to increase the binding capability of microcantilever biosensors is represented by growing zinc oxide nanowires (ZnO NWs) on their active surface. ZnO NWs grown on silicon microcantilever arrays and activated with an innovative immobilization strategy enhanced the sensor binding capability of nearly 1 order of magnitude, with respect to the commonly employed flat functionalized silicon devices.

We report on the preparation and the piezoelectric properties of ultrathin polymeric nanowires in the oriented pores of mesoporous silica, which are embedded in the channels of a supporting anodic ...

A high flexible and easy conformable piezoresistive composite material was used and tested to fit in complex-shaped structures and to be suitably integrated onto the robot surface for tactile sensing. In order to obtain the functional material in the form of self standing multilayer thin samples, two process flows based on microcasting and hot embossing techniques were optimized. The influence of different composition parameters on the functional performances was investigated and a huge variation of the electrical resistance, up to nine orders of magnitude, was registered when a mechanical pressure was applied to the prepared samples.

This work presents a comprehensive investigation of the piezoresistive response of a metal-polymer composite for robotic tactile sensor application. Composite samples, based on nickel nanostructured conductive filler in a polydimetihylsiloxane (PDMS) insulating elastomeric matrix, were prepared changing several process parameters like thickness, composition of the polymer and nickel filler content. A variation of electric resistance up to nine orders of magnitude under applied uniaxial load was measured in the fabricated samples. Cost efficient materials, simplicity of the process, large sensibility, and harsh environment compatibility make this quantum tunnelling composite adapted to be integrated as sensing coating in space robotic applications.