Real-Time Radiation Beam Monitoring by Flexible Perovskite Thin Film Arrays.

Real-time and in-line transversal monitoring of ionizing radiation beams is a crucial task for several applications which span from medical treatments to particle accelerators in high energy physics. Here a flexible and large area device based on 2D hybrid perovskite thin films (phenylethylammonium lead bromide), fabricated onto a thin flexible polyimide substrate, able to map the transversal beam profile of high energy radiation beams is reported. The performance of this novel tool is here compared with the one offered by standard commercial large-area technology, namely radiochromic sheets. The great potential of this class of devices is demonstrated by successfully mapping in real-time a 5 MeV proton beam at fluxes between 108 and 1010 H+ s-1 cm-2, confirming the capability to operate in a radiation-harsh environment without output signal saturation issues. The versatility and scalability of here proposed detecting system are demonstrated by the development of a multipixel array able to map in real-time a 40 kVp X-ray beam spot (dose rate 8 mGy s-1). Perovskite thin film-based detectors are thus assessed as a very promising class of thin, flexible devices for real-time, in-line, large-area, conformable, reusable, transparent, and low-cost transversal beam monitoring of different ionizing radiation.

Subsurface Profiling of Ion Migration and Swelling in Conducting Polymer Actuators with Modulated Electrochemical Atomic Force Microscopy.

Understanding the dynamics of ion migration and volume change is crucial to studying the functionality and long-term stability of soft polymeric materials operating at liquid interfaces, but the subsurface characterization of swelling processes in these systems remains elusive. In this work, we address the issue using modulated electrochemical atomic force microscopy as a depth-sensitive technique to study electroswelling effects in the high-performance actuator material polypyrrole doped with dodecylbenzenesulfonate (Ppy:DBS). We perform multidimensional measurements combining local electroswelling and electrochemical impedance spectroscopies on microstructured Ppy:DBS actuators. We interpret charge accumulation in the polymeric matrix with a quantitative model, giving access to both the spatiotemporal dynamics of ion migration and the distribution of electroswelling in the electroactive polymer layer. The findings demonstrate a nonuniform distribution of the effective ionic volume in the Ppy:DBS layer depending on the film morphology and redox state. Our findings indicate that the highly efficient actuation performance of Ppy:DBS is caused by rearrangements of the polymer microstructure induced by charge accumulation in the soft polymeric matrix, increasing the effective ionic volume in the bulk of the electroactive film for up to two times the value measured in free water.

Electrochemically actuated microelectrodes for minimally invasive peripheral nerve interfaces.

Electrode arrays that interface with peripheral nerves are used in the diagnosis and treatment of neurological disorders; however, they require complex placement surgeries that carry a high risk of nerve injury. Here we leverage recent advances in soft robotic actuators and flexible electronics to develop highly conformable nerve cuffs that combine electrochemically driven conducting-polymer-based soft actuators with low-impedance microelectrodes. Driven with applied voltages as small as a few hundreds of millivolts, these cuffs allow active grasping or wrapping around delicate nerves. We validate this technology using in vivo rat models, showing that the cuffs form and maintain a self-closing and reliable bioelectronic interface with the sciatic nerve of rats without the use of surgical sutures or glues. This seamless integration of soft electrochemical actuators with neurotechnology offers a path towards minimally invasive intraoperative monitoring of nerve activity and high-quality bioelectronic interfaces.

Ionic Solvent Shell Drives Electroactuation in Organic Mixed Ionic-Electronic Conductors.

The conversion of electrochemical processes into mechanical deformation in organic mixed ionic-electronic conductors (OMIECs) enables artificial muscle-like actuators but is also critical for degradation processes affecting OMIEC-based devices. To provide a microscopic understanding of electroactuation, the modulated electrochemical atomic force microscopy (mEC-AFM) is introduced here as a novel in-operando characterization method for electroactive materials. The technique enables multidimensional spectroscopic investigations of local electroactuation and charge uptake giving access to the electroactuation transfer function. For poly(3,4-ethylenedioxythiophene) polystyrene sulfonate (PEDOT:PSS) based microelectrodes, the spectroscopic measurements are combined with multichannel mEC-AFM imaging, providing maps of local electroactuation amplitude and phase as well as surface morphology. The results demonstrate that the amplitude and timescales of electroactuation are governed by the drift motion of hydrated ions. Accordingly, slower water diffusion processes are not limiting, and the results illustrate how OMIEC microactuators can operate at sub-millisecond timescales.

High-Endurance Long-Term Potentiation in Neuromorphic Organic Electrochemical Transistors by PEDOT:PSS Electrochemical Polymerization on the Gate Electrode.

The brain exhibits extraordinary information processing capabilities thanks to neural networks that can operate in parallel with minimal energy consumption. Memory and learning require the creation of new neural networks through the long-term modification of the structure of the synapses, a phenomenon called long-term plasticity. Here, we use an organic electrochemical transistor to simulate long-term potentiation and depotentiation processes. Similarly to what happens in a synapse, the polymerization of the 3,4-ethylenedioxythiophene (EDOT) on the gate electrode modifies the structure of the device and boosts the ability of the gate potential to modify the conductivity of the channel. Operando AFM measurements were carried out to demonstrate the correlation between neuromorphic behavior and modification of the gate electrode. Long-term enhancement depends on both the number of pulses used and the gate potential, which generates long-term potentiation when a threshold of +0.7 V is overcome. Long-term depotentiation occurs by applying a +3.0 V potential and exploits the overoxidation of the deposited PEDOT:PSS. The induced states are stable for at least 2 months. The developed device shows very interesting characteristics in the field of neuromorphic electronics.

Tissue Equivalent Curved Organic X-ray Detectors Utilizing High Atomic Number Polythiophene Analogues.

Organic semiconductors are a promising material candidate for X-ray detection. However, the low atomic number (Z) of organic semiconductors leads to poor X-ray absorption thus restricting their performance. Herein, the authors propose a new strategy for achieving high-sensitivity performance for X-ray detectors based on organic semiconductors modified with high -Z heteroatoms. X-ray detectors are fabricated with p-type organic semiconductors containing selenium heteroatoms (poly(3-hexyl)selenophene (P3HSe)) in blends with an n-type fullerene derivative ([6,6]-Phenyl C71 butyric acid methyl ester (PC70 BM). When characterized under 70, 100, 150, and 220 kVp X-ray radiation, these heteroatom-containing detectors displayed a superior performance in terms of sensitivity up to 600 ± 11 nC Gy-1  cm-2 with respect to the bismuth oxide (Bi2 O3 ) nanoparticle (NP) sensitized organic detectors. Despite the lower Z of selenium compared to the NPs typically used, the authors identify a more efficient generation of electron-hole pairs, better charge transfer, and charge transport characteristics in heteroatom-incorporated detectors that result in this breakthrough detector performance. The authors also demonstrate flexible X-ray detectors that can be curved to a radius as low as 2 mm with low deviation in X-ray response under 100 repeated bending cycles while maintaining an industry-standard ultra-low dark current of 0.03 ± 0.01 pA mm-2 .

Photoinduced Current Transient Spectroscopy on Metal Halide Perovskites: Electron Trapping and Ion Drift.

Metal halide perovskites (MHPs) are disruptive materials for a vast class of optoelectronic devices. The presence of electronic trap states has been a tough challenge in terms of characterization and thus mitigation. Many attempts based on electronic spectroscopies have been tested, but due to the mixed electronic-ionic nature of MHP conductivity, many experimental results retain a large ambiguity in resolving electronic and ionic charge contributions. Here we adapt a method, previously used in highly resistive inorganic semiconductors, called photoinduced current transient spectroscopy (PICTS) on lead bromide 2D-like ((PEA)2PbBr4) and standard "3D" (MAPbBr3) MHP single crystals. We present two conceptually different outcomes of the PICTS measurements, distinguishing the different electronic and ionic contributions to the photocurrents based on the different ion drift of the two materials. Our experiments unveil deep level trap states on the 2D, "ion-frozen" (PEA)2PbBr4 and set new boundaries for the applicability of PICTS on 3D MHPs.

Safety injections of nuclear medicine radiotracers: towards a new modality for a real-time detection of extravasation events and 18F-FDG SUV data correction.

BACKGROUND: 18F-FDG PET/CT imaging allows to study oncological patients and their relative diagnosis through the standardised uptake value (SUV) evaluation. During radiopharmaceutical injection, an extravasation event may occur, making the SUV value less accurate and possibly leading to severe tissue damage. The study aimed to propose a new technique to monitor and manage these events, to provide an early evaluation and correction to the estimated SUV value through a SUV correction coefficient. METHODS: A cohort of 70 patients undergoing 18F- FDG PET/CT examinations was enrolled. Two portable detectors were secured on the patients' arms. The dose-rate (DR) time curves on the injected DRin and contralateral DRcon arm were acquired during the first 10 min of injection. Such data were processed to calculate the parameters ΔpinNOR = (DRinmax- DRinmean)/DRinmax and ΔRt = (DRin(t) - DRcon(t)), where DRinmax is the maximum DR value, DRinmean is the average DR value in the injected arm. OLINDA software allowed dosimetric estimation of the dose in the extravasation region. The estimated residual activity in the extravasation site allowed the evaluation of the SUV's correction value and to define an SUV correction coefficient. RESULTS: Four cases of extravasations were identified for which ΔRt [(390 ± 26) µSv/h], while ΔRt [(150 ± 22) µSv/h] for abnormal and ΔRt [(24 ± 11) µSv/h] for normal cases. The ΔpinNOR showed an average value of (0.44 ± 0.05) for extravasation cases and an average value of (0.91 ± 0.06) and (0.77 ± 0.23) in normal and abnormal classes, respectively. The percentage of SUV reduction (SUV%CR) ranges between 0.3% and 6%. The calculated self-tissue dose values range from 0.027 to 0.573 Gy, according to the segmentation modality. A similar correlation between the inverse of ΔpinNOR and the normalised ΔRt with the SUV correction coefficient was found. CONCLUSIONS: The proposed metrics allowed to characterised the extravasation events in the first few minutes after the injection, providing an early SUV correction when necessary. We also assume that the characterisation of the DR-time curve of the injection arm is sufficient for the detection of extravasation events. Further validation of these hypotheses and key metrics is recommended in larger cohorts.

Smart Bandaid Integrated with Fully Textile OECT for Uric Acid Real-Time Monitoring in Wound Exudate.

Hard-to-heal wounds (i.e., severe and/or chronic) are typically associated with particular pathologies or afflictions such as diabetes, immunodeficiencies, compression traumas in bedridden people, skin grafts, or third-degree burns. In this situation, it is critical to constantly monitor the healing stages and the overall wound conditions to allow for better-targeted therapies and faster patient recovery. At the moment, this operation is performed by removing the bandages and visually inspecting the wound, putting the patient at risk of infection and disturbing the healing stages. Recently, new devices have been developed to address these issues by monitoring important biomarkers related to the wound health status, such as pH, moisture, etc. In this contribution, we present a novel textile chemical sensor exploiting an organic electrochemical transistor (OECT) configuration based on poly(3,4-ethylenedioxythiophene):polystyrene sulfonate (PEDOT:PSS) for uric acid (UA)-selective monitoring in wound exudate. The combination of special medical-grade textile materials provides a passive sampling system that enables the real-time and non-invasive analysis of wound fluid: UA was detected as a benchmark analyte to monitor the health status of wounds since it represents a relevant biomarker associated with infections or necrotization processes in human tissues. The sensors proved to reliably and reversibly detect UA concentration in synthetic wound exudate in the biologically relevant range of 220-750 µM, operating in flow conditions for better mimicking the real wound bed. This forerunner device paves the way for smart bandages integrated with real-time monitoring OECT-based sensors for wound-healing evaluation.

Determination of Stiffness and the Elastic Modulus of 3D-Printed Micropillars with Atomic Force Microscopy-Force Spectroscopy.

Nowadays, many applications in diverse fields are taking advantage of micropillars such as optics, tribology, biology, and biomedical engineering. Among them, one of the most attractive is three-dimensional microelectrode arrays for in vivo and in vitro studies, such as cellular recording, biosensors, and drug delivery. Depending on the application, the micropillar's optimal mechanical response ranges from soft to stiff. For long-term implantable devices, a mechanical mismatch between the micropillars and the biological tissue must be avoided. For drug delivery patches, micropillars must penetrate the skin without breaking or bending. The accurate mechanical characterization of the micropillar is pivotal in the fabrication and optimization of such devices, as it determines whether the device will fail or not. In this work, we demonstrate an experimental method based only on atomic force microscopy-force spectroscopy that allows us to measure the stiffness of a micropillar and the elastic modulus of its constituent material. We test our method with four different types of 3D inkjet-printed micropillars: silver micropillars sintered at 100 and 150 °C and polyacrylate microstructures with and without a metallic coating. The estimated elastic moduli are found to be comparable with the corresponding bulk values. Furthermore, our findings show that neither the sintering temperature nor the presence of a thin metal coating plays a major role in defining the mechanical properties of the micropillar.

Mixed 3D-2D Perovskite Flexible Films for the Direct Detection of 5 MeV Protons.

This study reports on a novel, flexible, proton beam detector based on mixed 3D-2D perovskite films deposited by solution onto thin plastic foils. The 3D-2D mixture allows to obtain micrometer-thick and highly uniform films that constitute the detector's active layer. The devices demonstrate excellent flexibility with stable electric transport properties down to a bending radius of 3.1 mm. The detector is characterized under a 5 MeV proton beam with fluxes in the range [4.5 × 105 - 1.4 × 109 ] H+ cm-2 s-1 , exhibiting a stable response to repetitive irradiation cycles with sensitivity up to (290 ± 40) nC Gy-1 mm-3 and a limit of detection down to (72±2) µGy s-1 . The detector radiation tolerance is also assessed up to a total of 1.7 × 1012 protons impinging on the beam spot area, with a maximum variation of the detector's response of 14%.

AC amplification gain in organic electrochemical transistors for impedance-based single cell sensors.

Research on electrolyte-gated and organic electrochemical transistor (OECT) architectures is motivated by the prospect of a highly biocompatible interface capable of amplifying bioelectronic signals at the site of detection. Despite many demonstrations in these directions, a quantitative model for OECTs as impedance biosensors is still lacking. We overcome this issue by introducing a model experiment where we simulate the detection of a single cell by the impedance sensing of a dielectric microparticle. The highly reproducible experiment allows us to study the impact of transistor geometry and operation conditions on device sensitivity. With the data we rationalize a mathematical model that provides clear guidelines for the optimization of OECTs as single cell sensors, and we verify the quantitative predictions in an in-vitro experiment. In the optimized geometry, the OECT-based impedance sensor allows to record single cell adhesion and detachment transients, showing a maximum gain of 20.2±0.9 dB with respect to a single electrode-based impedance sensor.

In Situ Force Microscopy to Investigate Fracture in Stretchable Electronics: Insights on Local Surface Mechanics and Conductivity.

Stretchable conductors are of crucial relevance for emerging technologies such as wearable electronics, low-invasive bioelectronic implants, or soft actuators for robotics. A critical issue for their development regards the understanding of defect formation and fracture of conducting pathways during stress-strain cycles. Here we present a combination of atomic force microscopy (AFM) methods that provides multichannel images of surface morphology, conductivity, and elastic modulus during sample deformation. To develop the method, we investigate in detail the mechanical interactions between the AFM tip and a stretched, free-standing thin film sample. Our findings reveal the conditions to avoid artifacts related to sample bending modes or resonant excitations. As an example, we analyze strain effects in thin gold films deposited on a soft silicone substrate. Our technique allows one to observe the details of microcrack opening during tensile strain and their impact on local current transport and surface mechanics. We find that although the film fractures into separate fragments, at higher strain a current transport is sustained by a tunneling mechanism. The microscopic observation of local defect formation and their correlation to local conductivity will provide insight into the design of more robust and fatigue resistant stretchable conductors.

Organic Electrochemical Transistors as Versatile Tool for Real-Time and Automatized Viral Cytopathic Effect Evaluation.

In-vitro viral studies are still fundamental for biomedical research since studying the virus kinetics on cells is crucial for the determination of the biological properties of viruses and for screening the inhibitors of infections. Moreover, testing potential viral contaminants is often mandatory for safety evaluation. Nowadays, viral cytopathic effects are mainly evaluated through end-point assays requiring dye-staining combined with optical evaluation. Recently, optical-based automatized equipment has been marketed, aimed at the real-time screening of cell-layer status and obtaining further insights, which are unavailable with end-point assays. However, these technologies present two huge limitations, namely, high costs and the possibility to study only cytopathic viruses, whose effects lead to plaque formation and layer disruption. Here, we employed poly(3,4-ethylenedioxythiophene):poly(styrene sulfonate) (Pedot:Pss) organic electrochemical transistors (OECTs) for the real-time, electrical monitoring of the infection of cytolytic viruses, i.e., encephalomyocarditis virus (EMCV), and non-cytolytic viruses, i.e., bovine coronavirus (B-CoV), on cells. OECT data on EMCV were validated using a commercially-available optical-based technology, which, however, failed in the B-CoV titration analysis, as expected. The OECTs proved to be reliable, fast, and versatile devices for viral infection monitoring, which could be scaled up at low cost, reducing the operator workload and speeding up in-vitro assays in the biomedical research field.

Oxygen Gas Sensing Using a Hydrogel-Based Organic Electrochemical Transistor for Work Safety Applications.

Oxygen depletion in confined spaces represents one of the most serious and underestimated dangers for workers. Despite the existence of several commercially available and widely used gas oxygen sensors, injuries and deaths from reduced oxygen levels are still more common than for other hazardous gases. Here, we present hydrogel-based organic electrochemical transistors (OECTs) made with the conducting polymer poly(3,4-ethylenedioxythiophene): poly(styrene sulfonate) (PEDOT:PSS) as wearable and real-time oxygen gas sensors. After comparing OECT performances using liquid and hydrogel electrolytes, we identified the best PEDOT:PSS active layer and hydrogel coating (30 µm) combination for sensing oxygen in the concentration range of 13−21% (v/v), critical for work safety applications. The fast O2 solubilization in the hydrogel allowed for gaseous oxygen transduction in an electrical signal thanks to the electrocatalytic activity of PEDOT:PSS, while OECT architecture amplified the response (gain ~ 104). OECTs proved to have comparable sensitivities if fabricated on glass and thin plastic substrates, (−12.2 ± 0.6) and (−15.4 ± 0.4) µA/dec, respectively, with low power consumption (<40 µW). Sample bending does not influence the device response, demonstrating that our real-time conformable and lightweight sensor could be implemented as a wearable, noninvasive safety tool for operators working in potentially hazardous confined spaces.

Molecular Weight Tuning of Organic Semiconductors for Curved Organic-Inorganic Hybrid X-Ray Detectors.

Curved X-ray detectors have the potential to revolutionize diverse sectors due to benefits such as reduced image distortion and vignetting compared to their planar counterparts. While the use of inorganic semiconductors for curved detectors are restricted by their brittle nature, organic-inorganic hybrid semiconductors which incorporated bismuth oxide nanoparticles in an organic bulk heterojunction consisting of poly(3-hexylthiophene-2,5-diyl) (P3HT) and [6,6]-phenyl C71 butyric acid methyl ester (PC70 BM) are considered to be more promising in this regard. However, the influence of the P3HT molecular weight on the mechanical stability of curved, thick X-ray detectors remains less well understood. Herein, high P3HT molecular weights (>40 kDa) are identified to allow increased intermolecular bonding and chain entanglements, resulting in X-ray detectors that can be curved to a radius as low as 1.3 mm with low deviation in X-ray response under 100 repeated bending cycles while maintaining an industry-standard dark current of <1 pA mm-2 and a sensitivity of ≈ 0.17 µC Gy-1 cm-2 . This study identifies a crucial missing link in the development of curved detectors, namely the importance of the molecular weight of the polymer semiconductors used.

A Wearable Electrochemical Gas Sensor for Ammonia Detection.

The next future strategies for improved occupational safety and health management could largely benefit from wearable and Internet of Things technologies, enabling the real-time monitoring of health-related and environmental information to the wearer, to emergency responders, and to inspectors. The aim of this study is the development of a wearable gas sensor for the detection of NH3 at room temperature based on the organic semiconductor poly(3,4-ethylenedioxythiophene) (PEDOT), electrochemically deposited iridium oxide particles, and a hydrogel film. The hydrogel composition was finely optimised to obtain self-healing properties, as well as the desired porosity, adhesion to the substrate, and stability in humidity variations. Its chemical structure and morphology were characterised by infrared spectroscopy and scanning electron microscopy, respectively, and were found to play a key role in the transduction process and in the achievement of a reversible and selective response. The sensing properties rely on a potentiometric-like mechanism that significantly differs from most of the state-of-the-art NH3 gas sensors and provides superior robustness to the final device. Thanks to the reliability of the analytical response, the simple two-terminal configuration and the low power consumption, the PEDOT:PSS/IrOx Ps/hydrogel sensor was realised on a flexible plastic foil and successfully tested in a wearable configuration with wireless connectivity to a smartphone. The wearable sensor showed stability to mechanical deformations and good analytical performances, with a sensitivity of 60 ± 8 µA decade-1 in a wide concentration range (17-7899 ppm), which includes the safety limits set by law for NH3 exposure.

X-Ray-Induced Modification of the Photophysical Properties of MAPbBr3 Single Crystals.

Methylammonium lead tribromide (MAPbBr3) perovskite single crystals demonstrate to be excellent direct X-ray and gamma-ray detectors with outstanding sensitivity and low limit of detection. Despite this, thorough studies on the photophysical effects of exposure to high doses of ionizing radiation on this material are still lacking. In this work, we present our findings regarding the effects of controlled X-ray irradiation on the optoelectronic properties of MAPbBr3 single crystals. Irradiation is carried out in air with an imaging X-ray tube, simulating real-life application in a medical facility. By means of surface photovoltage spectroscopy, we find that X-ray exposure quenches free excitons in the material and introduces new bound excitonic species. Despite this drastic effect, the crystals recover after 1 week of storage in dark and low humidity conditions. By means of X-ray photoelectron spectroscopy, we find that the origin of the new bound excitonic species is the formation of bromine vacancies, leading to local changes in the dielectric response of the material. The recovery effect is attributed to vacancy filling by atmospheric oxygen and water.

Atomic Force Microscopy Nanomechanics of Hard Nanometer-Thick Films on Soft Substrates: Insights into Stretchable Conductors.

The nanomechanical properties of ultrathin and nanostructured films of rigid electronic materials on soft substrates are of crucial relevance to realize materials and devices for stretchable electronics. Of particular interest are bending deformations in buckled nanometer-thick films or patterned networks of rigid materials as they can be exploited to compensate for the missing tensile elasticity. Here, we perform atomic force microscopy indentation experiments and electrical measurements to characterize the nanomechanics of ultrathin gold films on a polydimethylsiloxane (PDMS) elastomer. The measured force-indentation data can be analyzed in terms of a simple analytical model describing a bending plate on a semi-infinite soft substrate. The resulting method enables us to quantify the local Young's modulus of elasticity of the nanometer-thick film. Systematic variation of the gold layer thickness reveals the presence of a diffuse interface between the metal film and the elastomer substrate that does not contribute to the bending stiffness. The effect is associated with gold clusters that penetrate the silicone and are not directly connected to the ultrathin film. Only above a critical layer thickness, percolation of the metallic thin film happens, causing a linear increase in bending stiffness and electrical conductivity.

Advanced Wound Dressing for Real-Time pH Monitoring.

The rapid evolution of wearable technologies is giving rise to a strong push for textile chemical sensors design targeting the real-time collection of vital parameters for improved healthcare. Among the most promising applications, monitoring of nonhealing wounds is a scarcely explored medical field that still lacks quantitative tools for the management of the healing process. In this work, a smart bandage is developed for the real-time monitoring of wound pH, which has been reported to correlate with the healing stages, thus potentially giving direct access to the wound status without disturbing the wound bed. The fully textile device is realized by integrating a sensing layer, including the two-terminal pH sensor made of a semiconducting polymer and iridium oxide particles, and an absorbent layer ensuring the delivery of a continuous wound exudate flow across the sensor area. The two-terminal sensor exhibits a reversible response with a sensitivity of (59 ± 4) µA pH-1 in the medically relevant pH range for wound monitoring (pH 6-9), and its performance is not substantially affected either by the presence of the most common chemical interferents or by temperature gradients from 22 to 40 °C. Thanks to the robust sensing mechanism based on potentiometric transduction and the simple device geometry, the fully assembled smart bandage was successfully validated in flow analysis using synthetic wound exudate.