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In this paper, for the first time to the best of our knowledge, organic electrochemical transistors are employed to investigate the electrical response of human blood, plasma and alternative buffer solutions that inhibit red blood cell (RBC) aggregation. Our focus is on selecting a suitable electrolytic platform and the related operating conditions, where the RBC effect on the OECT response can be observed separately from the strong ionic environment of plasma in whole blood. The transient response of whole blood to pulse experiments is characterized by two time constants, which can be related to blood viscosity and to the capacitive coupling between the ionic and electronic components of the overall system. The role of capacitive effects, likely due to enhanced double-layer formation by negatively charged RBCs, is also confirmed by the increase of transconductance which was found in RBC suspensions as compared to the suspending buffer. Overall, the complex behavior found in these experiments provides new insights for the development of innovative blood-based sensing devices for biomedical applications.

A programmable dynamic cell culture chamber compatible with a standard multi-well plate was designed and characterized. The system is integrated with an array of OECT biosensors, in view of an in-situ monitoring of the dynamic cultures.

In this work a new Single Layer Graphene (SLG) transfer technique exploiting a hot embossing process was carried out. Flexible electrolyte gated Graphene Field Effect Transistors (G-FET) were fabricated and tested electrically. A polymeric transparent foil suitable for optics and flexible electronics, Cyclic Olefin Copolymer (COC) was used as flexible substrate. Raman characterization confirmed that the new Hot Embossing Graphene Transfer (HEGT) is suitable for the deposition of SLG and the fabrication of G-FETs. A Comparison with SLG common transfer method was carried out and proven for G-FETs fabrication. The HEGT devices showed typical characteristics and maintained the same performances when the substrate was bent. This demonstrated that the HEGT allows for efficient transfer of high quality SLG on large area thus providing the opportunity for the exploitation on a large scale production process for flexible substrates.

Miniaturized low-cost sensors for volatile organic compounds (VOCs) have the potentiality to become a fundamental tool for indoor and outdoor air quality monitoring, to significantly improve everyday life. Layered double hydroxides (LDHs) belong to the class of anionic clays and are largely employed for NOx detection, while few results are reported on VOCs. In this work, a novel LDH coprecipitation method is proposed. For the first time, a study comparing four LDHs (ZnAl-Cl, ZnFe-Cl, ZnAl-NO3, and MgAl-NO3) is carried out to investigate the sensing performances. As explored through several microscopy and spectroscopy analyses, LDHs show a morphology characterized by a large surface area and a three-dimensional hierarchical flowerlike architecture with micro- and nanopores that induce a fast diffusion and highly effective surface interaction of the target gases. The fabricated sensors, operating at room temperature, are able to reversibly and selectively detect acetone, ethanol, ammonia, and chlorine vapors, reaching significant sensing response values up to 6% at 21 degrees C. The results demonstrate that by changing the LDHs' composition, it is possible to modulate the sensitivity and selectivity of the sensor, helping the discrimination of different analytes, and the consequent integration on a sensor array paves the way for electronic nose development.

In several biomedical applications, the detection of biomarkers demands high sensitivity, selectivity and easy-to-use devices. Organic electrochemical transistors (OECTs) represent a promising class of devices combining a minimal invasiveness and good signal transduction. However, OECTs lack of intrinsic selectivity that should be implemented by specific approaches to make them well suitable for biomedical applications. Here, we report on a biosensor in which selectivity and a high sensitivity are achieved by interfacing, in an OECT architecture, a novel gate electrode based on aptamers, Au nanoparticles and graphene hierarchically organized to optimize the final response. The fabricated biosensor performs state of the art limit of detection monitoring biomolecules, such as thrombin-with a limit of detection in the picomolar range (≤ 5 pM) and a very good selectivity even in presence of supraphysiological concentrations of Bovine Serum Albumin (BSA-1mM). These accomplishments are the final result of the gate hierarchic structure that reduces sterich indrance that could contrast the recognition events and minimizes false positive, because of the low affinity of graphene towards the physiological environment. Since our approach can be easily applied to a large variety of different biomarkers, we envisage a relevant potential for a large series of different biomedical applications.

The effects of noise on any electronic system is a crucial aspect for the delineation of the proper functioning of circuits. Different and consolidated models have been proposed for classical electronic circuital elements but the effect of noise sourcing on memristive devices still lacks a wide and rich experimental description. Despite the larger use of Gaussian white noise in the stimulation of memristive systems, the use of uniform white noise has been recently proposed as a possible method for underlining variations in the impedance of an electronic device and in dynamic monitoring the system evolution. By applying uniform white noise to organic memristive devices (OMDs) while measuring the resulting current noise, we dynamically monitored the effects of noise amplitude on memristive properties. In fact OMDs functioning is based on the interfacial redox activity between polyaniline and a liquid electrolyte and constitutes an intrinsically impedance variation of the channel. We show that noise sourcing affects the hysteresis loops, the typical characteristics of electronic systems endowed with memory.

In the study of conductive conjugated polymers, electrical doping has long played an important role. A new polymeric gas sensor has been successfully fabricated by means of an ink-jet printer using a conductive aqueous formulation of poly(3,4-ethylenedioxythiophene) poly(styrene-sulfonate) (PEDOT:PSS). A simple yet robust treatment method for the irreversible secondary doping was performed (by H2SO4 and MeOH post-treatments) to enhance conductivity and improve gas sensing performance. Real time gas sensing measurements were carried out by exposing the devices with eight different analytes in a low concentrations range of VOCs vapors up to 5 % of the saturated vapor pressure, 10 ppm of NO2 and up to 10 % of relative humidity (RH) at 21 °C, exploiting dry air as carrier and diluting gas. The gas response, obtained as the ratio between the steady-state resistance variation and the baseline resistance of the device, was evaluated for different PEDOT:PSS post-treated sensors. An unexpected behavior of PEDOT:PSS post-treated with concentrated H2SO4 was observed, while MeOH and diluted H2SO4 post-treated sensors exhibited improved response towards all investigated analytes. The best performances were obtained towards 5 % of ammonia and NO2 with a gas response of 6 % and 28 % respectively with the device post-treated with pure methanol and 16 % with the sensor post-treated with diluted sulfuric acid. Furthermore, long-term stability and the influence of temperature were evaluated on the fabricated sensors. Altogether, these promising results allow a better understanding of the secondary doping effects on the electrical and sensing properties, paving the way for electronic nose development.

The perspective of downscaling organic electrochemical transistors (OECTs) in the nanorange is approached by depositing poly(3,4-ethylenedioxythiophene) polystyrene sulfonate (PEDOT:PSS) on electrodes with a nanogap designed and fabricated by electromigration induced break junction (EIBJ) technique. The electrical response of the fabricated devices is obtained by acquiring transfer characteristics in order to clarify the specific main characteristics of OECTs with sub-micrometer-sized active channels (nanogap-OECTs). On the basis of their electrical response to different scan times, the nanogap-OECT shows a maximum transconductance unaffected upon changing scan times in the time window from 1 s to 100 µs, meaning that fast varying signals can be easily acquired with unchanged amplifying performance. Hence, the scaling down of the channel size to the nanometer scale leads to a geometrical paradigm that minimizes effects on device response due to the cationic diffusion into the polymeric channel. A comprehensive study of these features is carried out by an electrochemical impedance spectroscopy (EIS) study, complemented by a quantitative analysis made by equivalent circuits. The propagation of a redox front into the polymer bulk due to ionic diffusion also known as the "intercalation pseudocapacitance" is identified as a limiting factor for the transduction dynamics.

The volatile nature of current variations in Organic electrochemical transistors (OECTs) is limiting their use in neuromorphic applications that demand not only temporary variations but also permanent modifications of the resistance states. Only a limited number of papers report on OECTs modified to achieve memristive/synaptic properties. Here we report a novel approach developed using standard organic electrochemical transistors combined with a graphene film as a gate electrode. We demonstrate that the proposed architecture could be optimized to achieve typical and unique non-volatile characteristics with neuromorphic-synaptic functionalities.

Two-step hot embossing process was used to transfer graphene and to fabricate Gr/Si Schottky photodiodes. As a direct graphene transfer technique, through a hot embossing system, CVD Gr monolayer was transferred from copper foil to Cyclic Olefin Copolymer (COC) foil without PMMA sacrificial layer. Then hot embossing was employed once again to bond graphene with the prepared Si substrate to form Schottky contact. Electrical and photoelectrical characterizations have been performed to evaluate the Schottky photodiode. The photocurrent increase linearly with light intensity under 633 nm illumination. With an appropriate bias voltage, the maximum responsivity reaches 0.73 A/W. Extracted from I-V characteristics by Cheung's function, the Schottky barrier height and ideality factor are 1.01 eV and 2.66, respectively. The experimental result shows the feasibility and effectiveness of this hot embossing fabrication process, which demonstrates the opportunity for large scale production and provides a new approach for graphene optoelectronics. This is the author's peer reviewed, accepted manuscript. However, the online version of record will be different from this version once it has been copyedited and typeset.

In this work an electrolyte gated Graphene field effect transistor (G-FET) has been developed exploiting a Hot-embossing assisted technique to transfer Single Layer Graphene (SLG) on a Cyclo Olefin Copolymer (COC) foil. An investigation on the processing and materials related effects has been carried out by a comparison with a more traditional Poly(methyl methacrylate) (PMMA) transfer approach. The fabricated G-FETs were tested as pH sensors and the electrical characteristics were investigated.

Performances in terms of efficiency and stability of dye-sensitized solar cells (DSSCs) depend on several factors related to the preparation of the device components (electrodes and electrolyte). In particular, patterning techniques recently intruded in the third generation photovoltaic scenario with promising results. In this perspective, we introduce the most interesting strategies proposed for the patterning of photoanodes and cathodes. Afterwards, we propose a novel approach exclusively based on the use of polymeric materials. The resulting DSSC shows a power conversion efficiency equal to 5.33% measured under 1 sun irradiation, and retains the 96% of this value in a prolonged aging test (2000 h at 50 °C).

Zinc oxide nanowires (ZnO NWs) were grown by a two-step growth method, involving the deposition of a patterned ZnO thin seeding layer and the chemical vapor deposition (CVD) of ZnO NWs. Two ways of patterning the seed layer were performed. The seeding solution containing ZnO precursors was deposited by sol–gel/spin-coating technique and patterned by photolithography. In the other case, the seeding solution was directly printed by inkjet printing only on selected portion of the substrate areas. In both cases, crystallization of the seed layer was achieved by thermal annealing in ambient air. Vertically aligned ZnO NWs were then grown by CVD on patterned, seeded substrates. The structure and morphology of ZnO NWs was analyzed by means of X-ray diffraction and field emission scanning electron microscopy measurements, respectively, while the vibrational properties were evaluated through Raman spectroscopy. Results showed that less-defective, vertically aligned, c-axis oriented ZnO NWs were grown on substrates patterned by photolithography while more defective nanostructures were grown on printed seed layer. A feature size of 30 µm was transferred into the patterned seed layer, and a good selectivity in growing ZnO NWs was obtained.

In-liquid biosensing is the new frontier of health and environment monitoring. A growing number of analytes and biomarkers of interest correlated to different diseases have been found, and the miniaturized devices belonging to the class of biosensors represent an accurate and cost-effective solution to obtaining their recognition. In this study, we investigate the effect of the solvent and of the substrate modification on thin films of organic semiconductor Poly(3-hexylthiophene) (P3HT) in order to improve the stability and electrical properties of an Electrolyte Gated Organic Field Effect Transistor (EGOFET) biosensor. The studied surface is the relevant interface between the P3HT and the electrolyte acting as gate dielectric for in-liquid detection of an analyte. Atomic Force Microscopy (AFM) and X-ray Photoelectron Spectroscopy (XPS) characterizations were employed to study the effect of two solvents (toluene and 1,2-dichlorobenzene) and of a commercial adhesion promoter (Ti Prime) on the morphological structure and electronic properties of P3HT film. Combining the results from these surface characterizations with electrical measurements, we investigate the changes on the EGOFET performances and stability in deionized (DI) water with an Ag/AgCl gate electrode.

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.

The scaling paradigm known as Moore's Law, with the shrinking of transistors and their doubling on a chip every two years, is going to reach a painful end. Another less-known paradigm, the so-called Koomey's Law, stating that the computing efficiency doubles every 1.57 years, poses other important challenges, since the efficiency of rechargeable energy sources is substantially constant, and any other evolution is based on device architecture only. How can we still increase the computational power/reduce the power consumption of our electronic environments? A first answer to this question comes from the quest for new functionalities. Within this aim, negative capacitance (NC) is becoming one of the most intriguing and studied phenomena since it can be exploited for reducing the aforementioned limiting effects in the downscaling of electronic devices. Here we report the evidence of negative capacitance in 80 nm thick ZnO thin films sputtered on Au interdigital electrodes (IDEs). Highly (002)-oriented ZnO thin films, with a fine-grained surface nanostructure and the desired chemical composition, are deposited at room temperature on different IDEs structures. Direct-current electrical measurements highlighted the semiconducting nature of ZnO (current density in the order of 1 × 10(-3) A/cm(2)). When turned into the alternating current regime (from 20 Hz to 2 MHz) the presence of NC values is observed in the low-frequency range (20-120 Hz). The loss of metal/semiconductor interface charge states under forward bias conditions, together with the presence of oxygen vacancies and piezoelectric/electrostriction effects, is believed to be at the basis of the observed negative behavior, suggesting that ZnO thin-film-based field-effect transistors can be a powerful instrument to go beyond the Boltzmann limit and the downscaling of integrated circuit elements required for the fabrication of portable and miniaturized electronic devices, especially for electric household appliances working in the low 50 Hz utility frequency.

In this work we report on the fabrication process for the development of a flexible piezopolymeric transducer for health monitoring applications, based on lead-free, piezoelectric zinc oxide (ZnO) thin films. All the selected materials are compatible with the space environment and were deposited by the RF magnetron sputtering technique at room temperature, in view of preserving the total flexibility of the structures, which is an important requirement to guarantee coupling with cylindrical fuel tanks whose integrity we want to monitor. The overall transducer architecture was made of a c-axis-oriented ZnO thin film coupled to a pair of flexible Polyimide foils coated with gold (Au) electrodes. The fabrication process started with the deposition of the bottom electrode on Polyimide foils. The ZnO thin film and the top electrode were then deposited onto the Au/Polyimide substrates. Both the electrodes and ZnO layer were properly patterned by wet-chemical etching and optical lithography. The assembly of the final structure was then obtained by gluing the upper and lower Polyimide foils with an epoxy resin capable of guaranteeing low outgassing levels, as well as adequate thermal and electrical insulation of the transducers. The piezoelectric behavior of the prototypes was confirmed and evaluated by measuring the mechanical displacement induced from the application of an external voltage.

Smart surfaces with a tunable wetting behavior between superhydrophobic and superhydrophilic states are of great interest for different applications, such as novel self-cleaning/antifogging layers, or in view of the development of microfluidic devices and chemical/biochemical sensors of new generation. This work shows the tuning of the wetting behavior of hydrothermally grown zinc oxide nanowires (NWs) by combining the dual effect resulting from either surface chemical functionalization of the NWs and their growth on substrates prepatterned with different micro-sized geometries. The characterization results highlight that vertically aligned ZnO NWs successfully cover all the microfeatures of the patterned substrates and can be successfully functionalized with aminopropyl groups. This chemical functionalization drives the initial transition of as-prepared, superhydrophilic ZnO NWs toward a superhydrophobic regime. Then, protonation/deprotonation of amine groups, induced by their interaction with acid or basic media, changes the wetting state of ZnO NWs between hydrophilic and hydrophobic regimes. Reversible and successful switching from hydrophobic to hydrophilic states can be achieved under ad hoc conditions, in particular using appropriate micropatterns that do not favor the formation and entrapment of air bubbles.

The effect of micro and nanostructuration on the piezoelectric properties of polymeric samples was studied in the present work. We prepared micro-sized pillars and nano-wires (thus one-dimensional structures) of a piezoelectric polymer Poly(VinyliDene Fluoride-Tri FluoroEthylene) PVDF-TrFE and we compared their structural and piezoelectrical properties with a thin film (thus two-dimensional) of the same material. X-ray diffraction and infrared spectroscopy measurements showed that the crystallization of the polymer into the ferroelectric ?-phase is affected by the size of the confinement. The piezoelectric characterization of the three polymeric structures showed important improvements as far as the nanostructuration is reached. Application as tactile sensor devices is therefore under development. © 2012 IEEE.