On the Interpretation of Hysteresis Loop for Electronic and Ionic Currents in Organic Memristive Devices

Being promising elements for neuromorphic computation, memristive devices have been often described as crucial elements for mimicking important synapse properties, such as memory and learning. Among them, organic memristive devices (OMDs) can claim low-cost fabrication processes and the easy tunability of their electrical properties. Up to now, the major bottleneck for their larger uses in neuromorphic computation is low rate of the resistance switching and stability. Herein, a new approach is reported, based on the use of a liquid electrolyte, leading to the manufacturing of OMD with higher stability and faster resistive switching

Electrical conductivity modulation of crosslinked composite nanofibers based on PEO and PEDOT:PSS

The aim of this work is to investigate the development of nanofiber mats, based on intrinsically conductive polymers (ICPs), which show simultaneously a high electrical conductivity and mandatory insoluble water properties. In particular, the nanofibers, thanks to their properties such as high surface area, porosity, and their ability to offer a preferential pathway for electron flow, play a crucial role to improve the essential characteristics ensured by ICPs. The nanofiber mats are obtained by electrospinning process, starting from a polymeric solution made of polyethylene oxide (PEO) and poly(styrene sulfonate) (PEDOT:PSS). PEO is selected not only as a dopant to increase the electrical/ionic conductivity, as deeply reported in the literature, but also to ensure the proper stability of the polymeric jet, to collect a dried nanofiber mat. Moreover, in the present work, two different treatments are proposed in order to induce crosslinking between PEO chains and PEDOT:PSS, made insoluble into water which is the final sample. The first process is based on a heating treatment, conducted at 130°C under nitrogen atmosphere for 6 h, named the annealing treatment. The second treatment is provided by UV irradiation that is effective to induce a final crosslinking, when a photoinitiator, such as benzophenone, is added. Furthermore, we demonstrate that both crosslinking treatments can be used to verify the preservation of nanostructures and their good electrical conductivity after water treatment (i.e., water resistance). In particular, we confirm that the crosslinking method with UV irradiation results to being more effective than the standard annealing treatment. Indeed, we demonstrate that the processing time, required to obtain the final crosslinked nanofiber mats with a high electrical conductance, results to being smaller than the one needed during the heating treatment

Focalization performance study of a novel bulk acoustic wave device

This work illustrates focalization performances of a silicon‐based bulk acoustic wave device applied for the separation of specimens owing to micrometric dimensions. Samples are separated in the microfluidic channel by the presence of an acoustic field, which focalizes particles or cells according to their mechanical properties compared to the surrounded medium ones. Design and fabrication processes are reported, followed by focalization performance tests conducted either with synthetic particles or cells. High focalization performances occurred at different microparticle concentrations. In addition, preliminary tests carried out with HL‐60 cells highlighted an optimal separation performance at a high flow rate and when cells are mixed with micro and nanoparticles without affecting device focalization capabilities. These encouraging results showed how this bulk acoustic wave device could be exploited to develop a diagnostic tool for early diagnosis or some specific target therapies by separating different kinds of cells or biomarkers possessing different mechanical properties such as shapes, sizes and densities

Flexible and reusable parylene C mask technology for applications in cascade impactor air quality monitoring systems

The development of traceable new methodologies to quantify elemental air pollutants in particulate matter (PM) supports modernization of methods used in air quality monitoring networks in Europe. In the framework of the EURAMET EMPIR AEROMET II project, the combination of cascade impactor aerosol sampling and total reflection X-ray fluorescence elemental spectroscopy (TXRF) was investigated. This technique requires a traceable calibration based on reference samples. This paper describes a new, simple and effective method to produce such reference samples using flexible, reusable, and low-cost parylene C shadow masks, fabricated by photolithographic steps. These shadow masks can be used to produce reference samples that mimic the Dekati cascade impactor's deposition patterns by applying as-prepared micro stencils to 30 mm acrylic substrates and evaporating a reference material (Ti) in arrangements of thin circular dots. The highly flexible direct patterning of acrylic discs with reference material, otherwise impossible with conventional photolithography, allows multiple reusing of the same micro stencils. The aspect ratios of the dots could be repeated with an error less than 4%. A first set of standard reference samples for the 13 stages of the Dekati cascade impactor was produced and preliminary TXRF measurements of the deposited Ti masses were performed. The centricity of the deposition patterns turned out to be an important parameter for the quality of the TXRF results. The parylene mask technology for the production of reference samples turns out to be a promising new approach for the traceable calibration of TXRF spectrometers for the quantification of element concentrations in environmental aerosol samples but, due to its great versatility, it could be used for several other micropatterning applications on conventional and unconventional substrates

Interfacing aptamers, nanoparticles and graphene in a hierarchical structure for highly selective detection of biomolecules in OECT devices

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

Hollow core waveguide for simultaneous laser plastic welding

Welding of plastics is a very important process in many industrial fields such as electronic packaging, medical applications, textile joining and automotive. It is often used when finished structure is too large to mold, for cost effectiveness or when dissimilar materials have to be joined. It is also employed in MEMs and Bio-MEMs applications, for example for microfluidic devices, where joint areas are very small, and need an amount of precision that other techniques can’t provide. This work focuses on description of transparent laser plastic welding technique, comparing simultaneous and quasi-simultaneous welding, and the development of an experimental setup for an automotive application. There are different laser welding methods, like simultaneous welding, where all the joining interface is irradiated at the same time and often includes a hollow guide to direct laser beam, and quasi-simultaneous welding, for example contour welding or scanning welding, where the laser spot is driven on joining interface via movement of the source or changing the path of the laser beam. An innovative tool end experimental setup was made to evaluate the simultaneous versus quasi-simultaneous welding to join polymeric material for an automotive application. A DFSS design of experiment was used. A LIMO laser bar diode @808nm with a maximum output power of 50 Watts, was coupled to a multi-mode 400 μm glass core optical fiber (Boscottica) with a numerical aperture of 0.22, by a LIMO Beam Transformation System HOC 150/500 (1401.612). The beam at the output of the fiber was guided through two different optical systems to the welding joint to test the two methods. A SANYO stepper motor was used for the quasi-simultaneous welding. Different kind of plastic materials were joined, Hostacom TRC 787N and THERMORUN TT875NE/BE. We performed static pull tests and dynamic pull test, and found optimum and baseline configuration

PEDOT:PSS Morphostructure and ion-to-electron transduction and amplification mechanisms in organic electrochemical transistors

Organic electrochemical transistors (OECTs) represent a powerful and versatile type of organic-based device, widely used in biosensing and bioelectronics due to potential advantages in terms of cost, sensitivity, and system integration. The benchmark organic semiconductor they are based on is poly(3,4-ethylenedioxythiophene):polystyrene sulfonate (PEDOT:PSS), the electrical properties of which are reported to be strongly dependent on film morphology and structure. In particular, the literature demonstrates that film processing induces morphostructural changes in terms of conformational rearrangements in the PEDOT:PSS in-plane phase segregation and out-of-plane vertical separation between adjacent PEDOT-rich domains. Here, taking into account these indications, we show the thickness-dependent operation of OECTs, contextualizing it in terms of the role played by PEDOT:PSS film thickness in promoting film microstructure tuning upon controlled-atmosphere long-lasting thermal annealing (LTA). To do this, we compared the LTA-OECT response to that of OECTs with comparable channel thicknesses that were exposed to a rapid thermal annealing (RTA). We show that the LTA process on thicker films provided OECTs with an enhanced amplification capability. Conversely, on lower thicknesses, the LTA process induced a higher charge carrier modulation when the device was operated in sensing mode. The provided experimental characterization also shows how to optimize the OECT response by combining the control of the microstructure via solution processing and the effect of postdeposition processing

Nanomolar detection of the antitumor drug tamoxifen by flexible organic electrochemical devices

Organic Electrochemical Transistors (OECTs) represent a versatile tool successfully exploited in the field of Bioelectronics. In particular, OECTs have been used for the detection of a wide set of bioanalytes, often showing superior performance compared to that of commonly used sensors. In this study, we propose a flexible, disposable OECT, based on poly (3,4-ethylenedioxythiophene):polystyrene sulfonate (PEDOT:PSS) channels and few layers graphene (FLG) sheets gate electrodes, for the detection of Tamoxifen (TAM), an important antitumor drug widely used in breast cancer therapy. The optimal device operation conditions in terms of sensitivity and limit of detection (LOD) have been investigated too

Total Reflection X-ray Fluorescence Reference Materials for Cascade Impactor Air Quality Monitoring Systems

The 12th International Conference on “Instrumental Methods of Analysis” www.ima2021.gr (accessed on 8 November 2021)), was organized by the Aristotle University of Thessaloniki and National Technical University of Athens, during 20–23 September 2021 as a virtual event, providing the opportunity for high-level analytical scientists from all around the world to promote their relevant research. IMA is a biannual series of conferences that started in 1999 and cover all areas of Chemical Analysis, including the development of new techniques, modern trends, and applications in a wide range of scientific disciplines. To date, several leading analytical chemists from Greece and abroad have presented their research work at previous IMA meetings. The 12th IMA conference (in a virtual format for the first time), had the ambition to bring together some of the most talented and innovative analytical chemists from all over the world for an excellent scientific online conference. The program of the 4-day event attended by 260 participants from 23 countries, included 14 invited speakers, 73 oral presentations, and 98 poster contributions. Covered topics included: spectrometric and electrometric analysis; chromatographic, mass spectrometric, microscopic, and thermal analysis methods; proteomics, metabolomics, metallomics, and elemental speciation analysis; chemical and biosensors; field analysis—mobile analytical instruments; miniaturized analytical systems (lab-on-a-chip), micro-, and nanofluidics; immunoassays and electrophoretic separation techniques; sampling techniques and strategies; robotics and automation; quality control—quality assurance in analysis; metrology; data processing and chemometrics; environmental analysis; biomedical (ecotoxicological and clinical) and pharmaceutical analysis; food analysis; materials analysis (nanomaterials, smart/advanced materials, and surface analysis); archaeometry; and analytical chemistry markets and possibilities for commercialization. Special sessions, focused on aerosol metrology (supported by EU Project AEROMET II), advanced X-ray techniques (supported by the European X-ray Spectrometry Association), and application of chemical analysis in the study of virus spread analytics (airborne and wastewaters), were also organized within the frame of IMA-2021

Single-Step 3D Printing of Silver-Patterned Polymeric Devices for Bacteria Proliferation Control

This work describes the fabrication of silver-patterned polymeric devices via light-based 3D printing methods from a tailored resin. An acrylate resin containing silver nitrate (AgNO3) as a silver precursor is employed to generate silver nanoparticles (AgNPs) through the in situ reduction of the metallic salt. The silver-based resin is processed through a customized stereolithography SL-3D printing to fabricate structures with silver-patterned surfaces. This customized SL-printer (emitting at 405 nm) offers the possibility of adjusting the machine settings during the printing process allowing for AgNPs to be selectively generated by modifying the laser settings during the 3D printing step. Thus, the resin photopolymerization and the photoinduced formation of AgNPs-based strands can be sequentially achieved during the same printing process with the same light source and using the same printable resin. The fabricated silver-patterned devices exhibit different surface features that might be exploited in systems working in a marine environment to control biofilm proliferation. As a proof-of-concept, the antimicrobial behavior of the silver-based 3D printed device is tested against environmental bacterial mixed communities via UV–vis spectroscopy and evaluating the absorbance change. Further tests, however, would be needed to reinforce the evidence of the bacteria behavior on the silver-patterned 3D printed devices