Multimodal force and temperature tactile sensor based on a short-channel organic transistor with high sensitivity.

In this manuscript, we report on a novel architecture for the fabrication of highly sensitive multimodal tactile transducers, for the simultaneous detection of temperature and force. Such devices are based on a flexible Organic Charge Modulated Field Effect Transistor (OCMFET) coupled with a pyro/piezoelectric element, namely a commercial film of poly-vinylene difluoride (PVDF). The reduction of the channel length, obtained by employing a low-resolution vertical channel architecture, allowed to maximize the ratio between the sensing area and the transistor's channel area, a technological approach that allows to considerably enhance both temperature and force sensitivity, while at the same time minimize the sensor's dimensions. Thanks to the employment of a straightforward, up-scalable, and highly reproducible fabrication process, this solution represents an interesting alternative for all those applications requiring high-density, high-sensitivity sensors such as robotics and biomedical applications.

Wearable System Based on Ultra-Thin Parylene C Tattoo Electrodes for EEG Recording.

In an increasingly interconnected world, where electronic devices permeate every aspect of our lives, wearable systems aimed at monitoring physiological signals are rapidly taking over the sport and fitness domain, as well as biomedical fields such as rehabilitation and prosthetics. With the intent of providing a novel approach to the field, in this paper we discuss the development of a wearable system for the acquisition of EEG signals based on a portable, low-power custom PCB specifically designed to be used in combination with non-conventional ultra-conformable and imperceptible Parylene-C tattoo electrodes. The proposed system has been tested in a standard rest-state experiment, and its performance in terms of discrimination of two different states has been compared to that of a commercial wearable device for EEG signal acquisition (i.e., the Muse headset), showing comparable results. This first preliminary validation demonstrates the possibility of conveniently employing ultra-conformable tattoo-electrodes integrated portable systems for the unobtrusive acquisition of brain activity.

Simultaneous recording of electrical and metabolic activity of cardiac cells in vitro using an organic charge modulated field effect transistor array.

In vitro electrogenic cells monitoring is an important objective in several scientific and technological fields, such as electrophysiology, pharmacology and brain machine interfaces, and can represent an interesting opportunity in other translational medicine applications. One of the key aspects of cellular cultures is the complexity of their behavior, due to the different kinds of bio-related signals, both chemical and electrical, that characterize these systems. In order to fully understand and exploit this extraordinary complexity, specific devices and tools are needed. However, at the moment this important scientific field is characterized by the lack of easy-to-use, low-cost devices for the sensing of multiple cellular parameters. To the aim of providing a simple and integrated approach for the study of in vitro electrogenic cultures, we present here a new solution for the monitoring of both the electrical and the metabolic cellular activity. In particular, we show here how a particular device called Micro Organic Charge Modulated Array (MOA) can be conveniently engineered and then used to simultaneously record the complete cell activity using the same device architecture. The system has been tested using primary cardiac rat myocytes and allowed to detect the metabolic and electrical variations thar occur upon the administration of different drugs. This first example could lay the basis for the development of a new generation of multi-sensing tools that can help to efficiently probe the multifaceted in vitro environment.

Epidermal Electrodes with Ferrimagnetic/Conductive Properties for Biopotential Recordings.

Interfacing ultrathin functional films for epidermal applications with external recording instruments or readout electronics still represents one of the biggest challenges in the field of tattoo electronics. With the aim of providing a convenient solution to this ever-present limitation, in this work we propose an innovative free-standing electrode made of a composite thin film based on the combination of the conductive polymer PEDOT:PSS and ferrimagnetic powder. The proposed epidermal electrode can be directly transferred onto the skin and is structured in two parts, namely a conformal conductive part with a thickness of 3 µm and a ferrimagnetic-conductive part that can be conveniently connected using magnetic connections. The films were characterized for ECG recordings, revealing a performance comparable to that of commercial pre-gelled electrodes in terms of cross-spectral coherence, signal-to-noise ratio, and baseline wandering. These new, conductive, magnetically interfaceable, and free-standing conformal films introduce a novel concept in the domain of tattoo electronics and can set the basis for the development of a future family of epidermal devices and electrodes.

Parylene C-Based, Breathable Tattoo Electrodes for High-Quality Bio-Potential Measurements.

A breathable tattoo electrode for bio-potential recording based on a Parylene C nanofilm is presented in this study. The proposed approach allows for the fabrication of micro-perforated epidermal submicrometer-thick electrodes that conjugate the unobtrusiveness of Parylene C nanofilms and the very important feature of breathability. The electrodes were fully validated for electrocardiography (ECG) measurements showing performance comparable to that of conventional disposable gelled Ag/AgCl electrodes, with no visible negative effect on the skin even many hours after their application. This result introduces interesting perspectives in the field of epidermal electronics, particularly in applications where critical on-body measurements are involved.

In Vitro Multiparametric Cellular Analysis by Micro Organic Charge-modulated Field-effect Transistor Arrays.

Modern electrophysiology has been constantly fueled by the parallel development of increasingly sophisticated tools and materials. In turn, discoveries in this field have driven technological progress in a back-and-forth process that ultimately determined the impressive achievements of the past 50 years. However, the most employed devices used for cellular interfacing (namely, the microelectrode arrays and microelectronic devices based on transistors) still present several limitations such as high cost, the rigidity of the materials, and the presence of an external reference electrode. To partially overcome these issues, there have been developments in a new scientific field called organic bioelectronics, resulting in advantages such as lower cost, more convenient materials, and innovative fabrication techniques. Several interesting new organic devices have been proposed during the past decade to conveniently interface with cell cultures. This paper presents the protocol for the fabrication of devices for cellular interfacing based on the organic charge-modulated field-effect transistor (OCMFET). These devices, called micro OCMFET arrays (MOAs), combine the advantages of organic electronics and the peculiar features of the OCMFET to prepare transparent, flexible, and reference-less tools with which it is possible to monitor both the electrical and the metabolic activities of cardiomyocytes and neurons in vitro, thus allowing a multiparametric evaluation of electrogenic cell models.

Dynamic Surface Electromyography Using Stretchable Screen-Printed Textile Electrodes.

OBJECTIVE: Wearable devices have created new opportunities in healthcare and sport sciences by unobtrusively monitoring physiological signals. Textile polymer-based electrodes proved to be effective in detecting electrophysiological potentials but suffer mechanical fragility and low stretch resistance. The goal of this research is to develop and validate in dynamic conditions cost-effective and easily manufacturable electrodes characterized by adequate robustness and signal quality. METHODS: We here propose an optimized screen printing technique for the fabrication of PEDOT:PSS-based textile electrodes directly into finished stretchable garments for surface electromyography (sEMG) applications. A sensorised stretchable leg sleeve was developed, targeting five muscles of interest in rehabilitation and sport science. An experimental validation was performed to assess the accuracy of signal detection during dynamic exercises, including sit-to-stand, leg extension, calf raise, walking, and cycling. RESULTS: The electrodes can resist up to 500 stretch cycles. Tests on five subjects revealed excellent contact impedance, and cross-correlation between sEMG envelopes simultaneously detected from the leg muscles by the textile and Ag/AgCl electrodes was generally greater than 0.9, which proves that it is possible to obtain good quality signals with performance comparable with disposable electrodes. CONCLUSIONS: An effective technique to embed polymer-based electrodes in stretchable smart garments was presented, revealing good performance for dynamic sEMG detections. SIGNIFICANCE: The achieved results pave the way to the integration of unobtrusive electrodes, obtained by screen printing of conductive polymers, into technical fabrics for rehabilitation and sport monitoring, and in general where the detection of sEMG in dynamic conditions is necessary.

Interfacing cells with organic transistors: a review of in vitro and in vivo applications.

Recently, organic bioelectronics has attracted considerable interest in the scientific community. The impressive growth that it has undergone in the last 10 years has allowed the rise of the completely new field of cellular organic bioelectronics, which has now the chance to compete with consolidated approaches based on devices such as micro-electrode arrays and ISFET-based transducers both in in vitro and in vivo experimental practice. This review focuses on cellular interfaces based on organic active devices and has the intent of highlighting the recent advances and the most innovative approaches to the ongoing and everlasting challenge of interfacing living matter to the "external world" in order to unveil the hidden mechanisms governing its behavior. Device-wise, three different organic structures will be considered in this work, namely the organic electrochemical transistor (OECT), the solution-gated organic transistor (SGOFET - which is presented here in two possible different versions according to the employed active material, namely: the electrolyte-gated organic transistor - EGOFET, and the solution gated graphene transistor - gSGFET), and the organic charge modulated field effect transistor (OCMFET). Application-wise, this work will mainly focus on cellular-based biosensors employed in in vitro and in vivo cellular interfaces, with the aim of offering the reader a comprehensive retrospective of the recent past, an overview of the latest innovations, and a glance at the future prospects of this challenging, yet exciting and still mostly unexplored scientific field.

Electrolyte-gated transistors for enhanced performance bioelectronics.

Electrolyte-gated transistors (EGTs), capable of transducing biological and biochemical inputs into amplified electronic signals and stably operating in aqueous environments, have emerged as fundamental building blocks in bioelectronics. In this Primer, the different EGT architectures are described with the fundamental mechanisms underpinning their functional operation, providing insight into key experiments including necessary data analysis and validation. Several organic and inorganic materials used in the EGT structures and the different fabrication approaches for an optimal experimental design are presented and compared. The functional bio-layers and/or biosystems integrated into or interfaced to EGTs, including self-organization and self-assembly strategies, are reviewed. Relevant and promising applications are discussed, including two-dimensional and three-dimensional cell monitoring, ultra-sensitive biosensors, electrophysiology, synaptic and neuromorphic bio-interfaces, prosthetics and robotics. Advantages, limitations and possible optimizations are also surveyed. Finally, current issues and future directions for further developments and applications are discussed.

A three-dimensional micro-electrode array for in-vitro neuronal interfacing.

OBJECTIVE: In this paper, we report on the development of an easy-to-fabricate three-dimensional Micro-Electrode Array (3D-MEA) specifically designed for brain-on-a-dish applications. APPROACH: The proposed device consists of pillar-shaped gold microelectrodes realized by electroplating directly on top of a standard MEA, making this approach highly versatile and convenient for batch fabrication. Moreover, with this simple technique, it is possible to obtain electrodes with a height of more than 100 µm onto different kind of substrates, ranging from glass to flexible plastic ones. MAIN RESULTS: This novel 3D-MEA structure has been validated with acute brain slices, successfully recording both epileptiform-like discharges (upon the administration of 4-AP), and electrically-evoked neuronal activity. The preliminary validation showed a substantial improvement in the signals amplitude with respect to both commercial and custom planar electrodes thanks to a better coupling offered by the peculiar shape of the three-dimensional electrodes. SIGNIFICANCE: Beside the versatility of the fabrication approach, which allows to obtain 3D MEA devices onto both rigid and flexible substrates, the reported validation showed how the pillar approach can outperform standard planar MEA recordings in terms of signal amplitude. Moreover, thanks to the possibility of obtaining multi-level 3D structures within the same device, the proposed fabrication technique offers an interesting and flexible approach for the development of a new family of electrophysiological tools for 3D in vitro electrophysiology, in particular for acute brain slices and 3D neuronal cultures for brain-on-a-dish applications.

Growing Patterned, Cross-linked Nanoscale Polymer Films from Organic and Inorganic Surfaces Using Ring-Opening Metathesis Polymerization.

The ability to modify substrates with thin polymer films allows for the tailoring of surface properties, and through combination of patterning finds use in a large variety of applications such as electronics and lab-on-chip devices. Although many techniques can be used to afford polymer-modified surfaces such as surface-initiated polymerization or layer-by-layer methodologies, their stability in a wide range of environments as well as their ability to target specific chemistry are critical factors to enable their successful application. In this paper, we report a facile technique in creating nanoscale polymer thin films using solid-state continuous assembly of polymers via ring-opening metathesis polymerization (ssCAPROMP) directly from surfaces functionalized through silanization. Using a polymeric precursor that includes norbornene moieties, a highly dense cross-linked network of polymer can be grown in a bottom-up fashion to afford thin films from an olefin-terminated silanized planar surface. Such nanotechnology affords films retaining the desirable qualities of previously reported methods while, at the same time, being covalently bound to the substrate: they are virtually pinhole free and can be reinitiated multiple times. By combining this process with microcontact printing, patterned films can be created by either the patterned deposition of a catalyst or by controlling the surface silanization chemistry and placement of olefin-terminated and nonreactive silanes. Additionally, patterned ssCAPROMP films were grown from SU-8 by selectively functionalizing the surface through masking and lift-off processes after the silanization step, thereby spatially controlling the surface-initiation, and subsequent polymer film formation. These patterned films expand the capabilities of the CAPROMP process and offer advantages over other film formation techniques in processes where patterned substrates and modified but robust surface chemistries are utilized.

From MEAs to MOAs: The Next Generation of Bioelectronic Interfaces for Neuronal Cultures.

Since their introduction in the early 1970s, microelectrode arrays (MEAs) have been dominating the electrophysiology market thanks to their reliability, extreme robustness, and usability. Over the past 40 years, silicon technology has also played a role in the advancement of the field, and CMOS-based in vitro and in vivo systems are now able to achieve unprecedented spatial resolutions, giving the possibility to unveil hidden behavior of cellular aggregates down to the subcellular level. However, both the MEAs and silicon-based electronic devices present unavoidable problems such as their expensiveness, the usual rigidity of the employed materials, and the need of an (usually bulky) external reference electrode. Possible interesting alternatives to these incredibly useful devices unexpectedly lie in the field of organic electronics, thanks to the fast-growing pace of improvement that this discipline has undergone in the last 10-15 years. In this chapter, a particular organic transistor called organic charge-modulated field-effect transistor (OCMFET) will be presented as a promising bio-electronic interface, and a complete description of its employment as a detector of cellular electrical activity and as an ultrasensitive pH sensor will be provided, together with the discussion about the possibility of using such a device as an innovative multisensing tool for both electrophysiology and (neuro)pharmacology.

Ultrathin, flexible and multimodal tactile sensors based on organic field-effect transistors.

In this study, a novel approach to the fabrication of a multimodal temperature and force sensor on ultrathin, conformable and flexible substrates is presented. This process involves coupling a charge-modulated organic field-effect transistor (OCMFET) with a pyro/piezoelectric element, namely a commercial film of poly-vinylene difluoride (PVDF). The proposed device is able to respond to both pressure stimuli and temperature variations, demonstrating the feasibility of the approach for the development of low-cost, highly sensitive and conformable multimodal sensors. The overall thickness of the device is 1.2 µm, being thus able to conform to any surface (including the human body), while keeping its electrical performance. Furthermore, it is possible to discriminate between simultaneously applied temperature and pressure stimuli by coupling sensing surfaces made of poled and unpoled spin-coated PVDF-trifluoroethylene (PVDF-TrFE, a PVDF copolymer) with OCMFETs. This demonstrates the possibility of creating multimodal sensors that can be employed for applications in several fields, ranging from robotics to wearable electronics.

Effects of homeopathic mother tinctures on breath alcohol testing.

In some countries, it is illegal to drive with any detectable amount of alcohol in blood; in others, the legal limit is 0.5 g/L or lower. Recently, some defendants charged with driving under the influence of alcohol and have claimed that positive breath alcohol test results were due to the ingestion of homeopathic mother tinctures. These preparations are obtained by maceration, digestion, infusion, or decoction of herbal material in hydroalcoholic solvent. A series of tests were conducted to evaluate the alcoholic content of three homeopathic mother tinctures and their ability to produce inaccurate breath alcohol results. Nine of 30 subjects gave positive results (0.11-0.82 g/L) when tests were taken within 1 min after drinking mother tincture. All tests taken at least 15 min after the mother tincture consumption and resulted in alcohol-free readings. An observation period of 15-20 min prior to breath alcohol testing eliminates the possibility of false-positive results.

Charge sensing by organic charge-modulated field effect transistors: application to the detection of bio-related effects.

The ability of field effect transistors (FETs) to detect charge variations on the gate may be exploited for realizing chemo- and bio-sensors. In this paper, we focus our attention on a particular kind of field effect device, named organic charge modulated FETs, whose features can be optimized for charge detection in liquid solutions. The results of the measurement of different bio-related effects are shown. In particular, DNA hybridization and pH detection in liquid media are proposed. Finally, preliminary considerations about the applicability of these devices to the detection of the electrical activity of cells are also provided. The device has considerable potential for being employed as a reliable, high sensitivity, low cost technology for sensing signals derived from living systems.