Graphene active sensor arrays for long-term and wireless mapping of wide frequency band epicortical brain activity

The role of electroencephalography in epilepsy research-From seizures to interictal activity and comorbidities

Electroencephalography (EEG) has been instrumental in epilepsy research for the past century, both for basic and translational studies. Its contributions have advanced our understanding of epilepsy, shedding light on the pathophysiology and functional organization of epileptic networks, and the mechanisms underlying seizures. Here we re-examine the historical significance, ongoing relevance, and future trajectories of EEG in epilepsy research. We describe traditional approaches to record brain electrical activity and discuss novel cutting-edge, large-scale techniques using micro-electrode arrays. Contemporary EEG studies explore brain potentials beyond the traditional Berger frequencies to uncover underexplored mechanisms operating at ultra-slow and high frequencies, which have proven valuable in understanding the principles of ictogenesis, epileptogenesis, and endogenous epileptogenicity. Integrating EEG with modern techniques such as optogenetics, chemogenetics, and imaging provides a more comprehensive understanding of epilepsy. EEG has become an integral element in a powerful suite of tools for capturing epileptic network dynamics across various temporal and spatial scales, ranging from rapid pathological synchronization to the long-term processes of epileptogenesis or seizure cycles. Advancements in EEG recording techniques parallel the application of sophisticated mathematical analyses and algorithms, significantly augmenting the information yield of EEG recordings. Beyond seizures and interictal activity, EEG has been instrumental in elucidating the mechanisms underlying epilepsy-related cognitive deficits and other comorbidities. Although EEG remains a cornerstone in epilepsy research, persistent challenges such as limited spatial resolution, artifacts, and the difficulty of long-term recording highlight the ongoing need for refinement. Despite these challenges, EEG continues to be a fundamental research tool, playing a central role in unraveling disease mechanisms and drug discovery.

Recent Advances in Nanomaterial-Based Biosignal Sensors

Recent research for medical fields, robotics, and wearable electronics aims to utilize biosignal sensors to gather bio-originated information and generate new values such as evaluating user well-being, predicting behavioral patterns, and supporting disease diagnosis and prevention. Notably, most biosignal sensors are designed for body placement to directly acquire signals, and the incorporation of nanomaterials such as metal-based nanoparticles or nanowires, carbon-based or polymer-based nanomaterials-offering stretchability, high surface-to-volume ratio, and tunability for various properties-enhances their adaptability for such applications. This review categorizes nanomaterial-based biosignal sensors into three types and analyzes them: 1) biophysical sensors that detect deformation such as folding, stretching, and even pulse, 2) bioelectric sensors that capture electric signal originating from human body such as heart and nerves, and 3) biochemical sensors that catch signals from bio-originated fluids such as sweat, saliva and blood. Then, limitations and improvements to nanomaterial-based biosignal sensors is depicted. Lastly, it is highlighted on deep learning-based signal processing and human-machine interface applications, which can enhance the potential of biosignal sensors. Through this paper, it is aim to provide an understanding of nanomaterial-based biosignal sensors, outline the current state of the technology, discuss the challenges that be addressed, and suggest directions for development.

Single-Walled Carbon Nanotubes as Optical Transducers for Nanobiosensors In Vivo

Semiconducting single-walled carbon nanotubes (SWCNTs) may serve as signal transducers for nanobiosensors. Recent studies have developed innovative methods of engineering molecularly specific sensors, while others have devised methods of deploying such sensors within live animals and plants. These advances may potentiate the use of implantable, noninvasive biosensors for continuous drug, disease, and contaminant monitoring based on the optical properties of single-walled carbon nanotubes (SWCNTs). Such tools have substantial potential to improve disease diagnostics, prognosis, drug safety, therapeutic response, and patient compliance. Outside of clinical applications, such sensors also have substantial potential in environmental monitoring or as research tools in the lab. However, substantial work remains to be done to realize these goals through further advances in materials science and engineering. Here, we review the current landscape of quantitative SWCNT-based optical biosensors that have been deployed in living plants and animals. Specifically, we focused this review on methods that have been developed to deploy SWCNT-based sensors in vivo as well as analytes that have been detected by SWCNTs in vivo. Finally, we evaluated potential future directions to take advantage of the promise outlined here toward field-deployable or implantable use in patients.

Multifunctional Integrated Biosensors Based on Two-Dimensional Field-Effect Transistors

In recent years, field-effect transistor (FET) sensing technology has attracted significant attention owing to its noninvasive, label-free, real-time, and user-friendly detection capabilities. Owing to the large specific surface area, high flexibility, and excellent conductivity of two-dimensional (2D) materials, FET biosensors based on 2D materials have demonstrated unique potential in biomarker analysis and healthcare applications, driving continuous innovation and transformation in the field. Here, we review recent trends in the development of 2D FET biosensors based on key performance metrics and main characteristics, and we also discuss structural designs and modification strategies for biosensing devices utilizing graphene, transition metal dichalcogenides, black phosphorus, and other 2D materials to enhance key performance metrics. Finally, we offer insights into future directions for biosensor advancements, discuss potential improvements, and present new recommendations for practical clinical applications.

Decoding sensorimotor information from somatosensory cortex by flexible epicorticalμECoG arrays in unrestrained behaving rats

Objective.Brain-computer interfaces (BCI) are promising for severe neurological conditions and there are ongoing efforts to develop state-of-the-art neural interfaces, hardware, and software tools. We tested the potential of novel reduced graphene oxide (rGO) electrodes implanted epidurally over the hind limb representation of the primary somatosensory (S1) cortex of rats, and compared them to commercial platinum-iridium (Pt-Ir) 16-channel electrodes (active site diameter: 25μm).Approach.Motor and somatosensory information was decoded offline from microelectrocorticography (μECoG) signals recorded while unrestrained rats performed a simple behavioral task: pressing a lever and the subsequent vibrotactile stimulation of the glabrous skin at three displacement amplitude levels and at two sinusoidal frequencies.μECoG data were initially analyzed by standard time-frequency methods. Next, signal powers of oscillatory bands recorded from multiple electrode channels were used as features for sensorimotor classification by a machine learning algorithm.Main results.Both electrode types performed quite well and similar to each other for predicting the motor interval and the presence of the vibrotactile stimulus. Average accuracies were relatively lower for predicting 3-class vibrotactile frequency and 4-class amplitude level by both electrode types.Significance.Given some confounding factors during the free movement of rats, the results show that both sensory and motor information can be recorded reliably from the hind limb area of S1 cortex by usingμECoG arrays. The chronic use of novel rGO electrodes was demonstrated successfully. The hind limb area may be convenient for the future evaluation of new tools in neurotechnology, especially those for bidirectional BCIs.

Flexible Graphene Field-Effect Transistors and Their Application in Flexible Biomedical Sensing

Flexible electronics are transforming our lives by making daily activities more convenient. Central to this innovation are field-effect transistors (FETs), valued for their efficient signal processing, nanoscale fabrication, low-power consumption, fast response times, and versatility. Graphene, known for its exceptional mechanical properties, high electron mobility, and biocompatibility, is an ideal material for FET channels and sensors. The combination of graphene and FETs has given rise to flexible graphene field-effect transistors (FGFETs), driving significant advances in flexible electronics and sparked a strong interest in flexible biomedical sensors. Here, we first provide a brief overview of the basic structure, operating mechanism, and evaluation parameters of FGFETs, and delve into their material selection and patterning techniques. The ability of FGFETs to sense strains and biomolecular charges opens up diverse application possibilities. We specifically analyze the latest strategies for integrating FGFETs into wearable and implantable flexible biomedical sensors, focusing on the key aspects of constructing high-quality flexible biomedical sensors. Finally, we discuss the current challenges and prospects of FGFETs and their applications in biomedical sensors. This review will provide valuable insights and inspiration for ongoing research to improve the quality of FGFETs and broaden their application prospects in flexible biomedical sensing.

Single-Step Functionalization Strategy of Graphene Microtransistor Array with Chemically Modified Aptamers for Biosensing Applications

Graphene solution-gated field-effect transistors (gSGFETs) offer high potential for chemical and biochemical sensing applications. Among the current trends to improve this technology, the functionalization processes are gaining relevance for its crucial impact on biosensing performance. Previous efforts are focused on simplifying the attachment procedure from standard multi-step to single-step strategies, but they still suffer from overreaction, and impurity issues and are limited to a particular ligand. Herein, a novel strategy for single-step immobilization of chemically modified aptamers with fluorenylmethyl and acridine moieties, based on a straightforward synthetic route to overcome the aforementioned limitations is presented. This approach is benchmarked versus a standard multi-step strategy using thrombin as detection model. In order to assess the reliability of the functionalization strategies 48-gSGFETs arrays are employed to acquire large datasets with multiple replicas. Graphene surface characterization demonstrates robust and higher efficiency in the chemical coupling of the aptamers with the single-step strategy, while the electrical response evaluation validates the sensing capability, allowing to implement different alternatives for data analysis and reduce the sensing variability. In this work, a new tool capable of overcome the functionalization challenges of graphene surfaces is provided, paving the way toward the standardization of gSGFETs for biosensing purposes.

Recent Advances in Two-Dimensional Nanomaterials for Healthcare Monitoring

The development of advanced technologies for the fabrication of functional nanomaterials, nanostructures, and devices has facilitated the development of biosensors for analyses. Two-dimensional (2D) nanomaterials, with unique hierarchical structures, a high surface area, and the ability to be functionalized for target detection at the surface, exhibit high potential for biosensing applications. The electronic properties, mechanical flexibility, and optical, electrochemical, and physical properties of 2D nanomaterials can be easily modulated, enabling the construction of biosensing platforms for the detection of various analytes with targeted recognition, sensitivity, and selectivity. This review provides an overview of the recent advances in 2D nanomaterials and nanostructures used for biosensor and wearable-sensor development for healthcare and health-monitoring applications. Finally, the advantages of 2D-nanomaterial-based devices and several challenges in their optimal operation have been discussed to facilitate the development of smart high-performance biosensors in the future.

Graphene-integrated mesh electronics with converged multifunctionality for tracking multimodal excitation-contraction dynamics in cardiac microtissues

Cardiac microtissues provide a promising platform for disease modeling and developmental studies, which require the close monitoring of the multimodal excitation-contraction dynamics. However, no existing assessing tool can track these multimodal dynamics across the live tissue. We develop a tissue-like mesh bioelectronic system to track these multimodal dynamics. The mesh system has tissue-level softness and cell-level dimensions to enable stable embedment in the tissue. It is integrated with an array of graphene sensors, which uniquely converges both bioelectrical and biomechanical sensing functionalities in one device. The system achieves stable tracking of the excitation-contraction dynamics across the tissue and throughout the developmental process, offering comprehensive assessments for tissue maturation, drug effects, and disease modeling. It holds the promise to provide more accurate quantification of the functional, developmental, and pathophysiological states in cardiac tissues, creating an instrumental tool for improving tissue engineering and studies.

Recent Advances in Laser-Induced Graphene-Based Materials for Energy Storage and Conversion

Laser-induced graphene (LIG) is a porous carbon nanomaterial that can be produced by irradiation of CO2 laser directly on the polymer substrate under ambient conditions. LIG has many merits over conventional graphene, such as simple and fast synthesis, tunable structure and composition, high surface area and porosity, excellent electrical and thermal conductivity, and good flexibility and stability. These properties make LIG a promising material for energy applications, such as supercapacitors, batteries, fuel cells, and solar cells. In this review, we highlight the recent advances of LIG in energy materials, covering the fabrication methods, performance enhancement strategies, and device integration of LIG-based electrodes and devices in the area of hydrogen evolution reaction, oxygen evolution reaction, oxygen reduction reaction, zinc-air batteries, and supercapacitors. This comprehensive review examines the potential of LIG for future sustainable and efficient energy material development, highlighting its versatility and multifunctionality in energy conversion.

A Nanozyme-Based Electrode for High-Performance Neural Recording

Implanted neural electrodes have been widely used to treat brain diseases that require high sensitivity and biocompatibility at the tissue-electrode interface. However, currently used clinical electrodes cannot meet both these requirements simultaneously, which hinders the effective recording of electronic signals. Herein, nanozyme-based neural electrodes incorporating bioinspired atomically precise clusters are developed as a general strategy with a heterogeneous design for multiscale and ultrasensitive neural recording via quantum transport and biocatalytic processes. Owing to the dual high-speed electronic and ionic currents at the electrode-tissue interface, the impedance of nanozyme electrodes is 26 times lower than that of state-of-the-art metal electrodes, and the acquisition sensitivity for the local field potential is ≈10 times higher than that of clinical PtIr electrodes, enabling a signal-to-noise ratio (SNR) of up to 14.7 dB for single-neuron recordings in rats. The electrodes provide more than 100-fold higher antioxidant and multi-enzyme-like activities, which effectively decrease 67% of the neuronal injury area by inhibiting glial proliferation and allowing sensitive and stable neural recording. Moreover, nanozyme electrodes can considerably improve the SNR of seizures in acute epileptic rats and are expected to achieve precise localization of seizure foci in clinical settings.

2D Materials in Flexible Electronics: Recent Advances and Future Prospectives

Flexible electronics have recently gained considerable attention due to their potential to provide new and innovative solutions to a wide range of challenges in various electronic fields. These electronics require specific material properties and performance because they need to be integrated into a variety of surfaces or folded and rolled for newly formatted electronics. Two-dimensional (2D) materials have emerged as promising candidates for flexible electronics due to their unique mechanical, electrical, and optical properties, as well as their compatibility with other materials, enabling the creation of various flexible electronic devices. This article provides a comprehensive review of the progress made in developing flexible electronic devices using 2D materials. In addition, it highlights the key aspects of materials, scalable material production, and device fabrication processes for flexible applications, along with important examples of demonstrations that achieved breakthroughs in various flexible and wearable electronic applications. Finally, we discuss the opportunities, current challenges, potential solutions, and future investigative directions about this field.

Graphene-based nanomaterials for peripheral nerve regeneration

Emerging nanotechnologies offer numerous opportunities in the field of regenerative medicine and have been widely explored to design novel scaffolds for the regeneration and stimulation of nerve tissue. In this review, we focus on peripheral nerve regeneration. First, we introduce the biomedical problem and the present status of nerve conduits that can be used to guide, fasten and enhance regeneration. Then, we thoroughly discuss graphene as an emerging candidate in nerve tissue engineering, in light of its chemical, tribological and electrical properties. We introduce the graphene forms commonly used as neural interfaces, briefly review their applications, and discuss their potential toxicity. We then focus on the adoption of graphene in peripheral nervous system applications, a research field that has gained in the last years ever-increasing attention. We discuss the potential integration of graphene in guidance conduits, and critically review graphene interaction not only with peripheral neurons, but also with non-neural cells involved in nerve regeneration; indeed, the latter have recently emerged as central players in modulating the immune and inflammatory response and accelerating the growth of new tissue.

Recent Advancements in Graphene-Based Implantable Electrodes for Neural Recording/Stimulation

Implantable electrodes represent a groundbreaking advancement in nervous system research, providing a pivotal tool for recording and stimulating human neural activity. This capability is integral for unraveling the intricacies of the nervous system's functionality and for devising innovative treatments for various neurological disorders. Implantable electrodes offer distinct advantages compared to conventional recording and stimulating neural activity methods. They deliver heightened precision, fewer associated side effects, and the ability to gather data from diverse neural sources. Crucially, the development of implantable electrodes necessitates key attributes: flexibility, stability, and high resolution. Graphene emerges as a highly promising material for fabricating such electrodes due to its exceptional properties. It boasts remarkable flexibility, ensuring seamless integration with the complex and contoured surfaces of neural tissues. Additionally, graphene exhibits low electrical resistance, enabling efficient transmission of neural signals. Its transparency further extends its utility, facilitating compatibility with various imaging techniques and optogenetics. This paper showcases noteworthy endeavors in utilizing graphene in its pure form and as composites to create and deploy implantable devices tailored for neural recordings and stimulations. It underscores the potential for significant advancements in this field. Furthermore, this paper delves into prospective avenues for refining existing graphene-based electrodes, enhancing their suitability for neural recording applications in in vitro and in vivo settings. These future steps promise to revolutionize further our capacity to understand and interact with the neural research landscape.

Electric Potential at the Interface of Membraneless Organelles Gauged by Graphene

Eukaryotic cells contain membrane-bound and membrane-less organelles that are often in contact with each other. How the interface properties of membrane-less organelles regulate their interactions with membranes remains challenging to assess. Here, we employ graphene-based sensors to investigate the electrostatic properties of synapsin 1, a major synaptic phosphoprotein, either in a single phase or after undergoing phase separation to form synapsin condensates. Using these graphene-based sensors, we discover that synapsin condensates generate strong electrical responses that are otherwise absent when synapsin is present as a single phase. By introducing atomically thin dielectric barriers, we show that the electrical response originates in an electric double layer whose formation governs the interaction between synapsin condensates and graphene. Our data indicate that the interface properties of the same protein are substantially different when the protein is in a single phase versus within a biomolecular condensate, unraveling that condensates can harbor ion potential differences at their interface.

Toward the Next Generation of Neural Iontronic Interfaces

Neural interfaces are evolving at a rapid pace owing to advances in material science and fabrication, reduced cost of scalable complementary metal oxide semiconductor (CMOS) technologies, and highly interdisciplinary teams of researchers and engineers that span a large range from basic to applied and clinical sciences. This study outlines currently established technologies, defined as instruments and biological study systems that are routinely used in neuroscientific research. After identifying the shortcomings of current technologies, such as a lack of biocompatibility, topological optimization, low bandwidth, and lack of transparency, it maps out promising directions along which progress should be made to achieve the next generation of symbiotic and intelligent neural interfaces. Lastly, it proposes novel applications that can be achieved by these developments, ranging from the understanding and reproduction of synaptic learning to live-long multimodal measurements to monitor and treat various neuronal disorders.

Emerging Penetrating Neural Electrodes: In Pursuit of Large Scale and Longevity

Penetrating neural electrodes provide a powerful approach to decipher brain circuitry by allowing for time-resolved electrical detections of individual action potentials. This unique capability has contributed tremendously to basic and translational neuroscience, enabling both fundamental understandings of brain functions and applications of human prosthetic devices that restore crucial sensations and movements. However, conventional approaches are limited by the scarce number of available sensing channels and compromised efficacy over long-term implantations. Recording longevity and scalability have become the most sought-after improvements in emerging technologies. In this review, we discuss the technological advances in the past 5-10 years that have enabled larger-scale, more detailed, and longer-lasting recordings of neural circuits at work than ever before. We present snapshots of the latest advances in penetration electrode technology, showcase their applications in animal models and humans, and outline the underlying design principles and considerations to fuel future technological development.

Upconversion optogenetics-driven biohybrid sensor for infrared sensing and imaging

Living organisms are far superior to state-of-the-art devices in visual perception as they have evolved a wide number of capabilities that encompass our most advanced technologies. By leveraging the performance of living organisms and directly interfacing them with artificial components, it can use the intricacy and metabolic efficiency of biological visual sensing within artificial machines. Inspired by the molecular basis (transient receptor potential, TRP) for infrared detection of pit-bearing organisms, we propose a TRP-like biohybrid sensor by integrating upconversion nanoparticles (UCNP) and optogenetically engineered cells on a graphene transistor for infrared sensing and imaging. The UCNP converts infrared light irradiation into blue light, the blue light activates the cells expressed with channelrhodopsin-2 (ChR2) and induces transmembrane photocurrent, and the photocurrent is detected by a biocompatible graphene transistor. Stepwise and overall experimental results show that, upon infrared light irradiation, the UCNP can rapidly mediate cellular photocurrents, which further translates into the extra output current of the graphene transistor. More notably, the response speed of the biohybrid sensor is 1∼3 orders of magnitude faster than those of TRPs heterologously expressed in cell lines in the literature, which confirms the response time advantage of the combination of UCNP and ChR2 within the sensor in place of TRPs. The biohybrid sensor can successfully image infrared targets, proving the feasibility of developing bionic infrared sensing devices by biohybrid integration of nonliving nanomaterials and biological components. This work opens up an avenue for biohybrid sensors to develop the bionic infrared vision that promisingly reproduces the functional superiority of natural organisms. STATEMENT OF SIGNIFICANCE: Infrared sensing and imaging have a wide range of military and civilian applications. Organisms have evolved excellent infrared vision with the molecular basis, transient receptor potential (TRP), and the performance is superior to existing state-of-the-art infrared devices. Inspired by this, a TRP-like biohybrid sensor based on upconversion optogenetics and a 2D material-based device is developed for infrared sensing and imaging. The biohybrid sensor has a relatively fast response speed that is 1∼3 orders of magnitude faster than that of the heterologously expressed TRPs, which enables its capability of infrared imaging with a single pixel-based method. This work broadens the spectrum of biohybrid sensing based on engineered cells to infrared, advancing the process of reproducing the excellent infrared detection of organisms.

Optimal twist angle for a graphene-like bilayer

The first optimal-or 'magic'-angle leading to the nullity of the Dirac/Fermi velocity for twisted bilayer graphene is re-evaluated in the Bistritzer-MacDonald set-up (Bistritzer and MacDonald 2011Proc. Natl Acad. Sci.10812233-7). From the details of that calculation we study the resulting alterations when the properties of the two layers are not exactly the same. A moiré combination of lattices without relative rotation but with different spacing lengths may also lead to a vanishing Dirac velocity. Hopping amplitudes can vary as well, and curvature is one of the possible causes for their change. In the case of small curvature values and situations dominated by hopping energy scales, the optimal angle becomes wider than in the 'flat' case.

Ferromagnetic Flexible Electronics for Brain-Wide Selective Neural Recording

Flexible microelectronics capable of straightforward implantation, remotely controlled navigation, and stable long-term recording hold great promise in diverse medical applications, particularly in deciphering complex functions of neural circuits in the brain. Existing flexible electronics, however, are often limited in bending and buckling during implantation, and unable to access a large brain region. Here, an injectable class of electronics with stable recording, omnidirectional steering, and precise navigating capabilities based on magnetic actuation is presented. After simple transcriptional injection, the rigid coatings are biodegraded quickly and the bundles of magnetic-nanoparticles-coated microelectrodes become separated, ultra-flexible, and magnetic actuated for further minimally invasive three-dimensional interpenetration in the brain. As proof of concept, this paradigm-shifting approach is demonstrated for selective and multiplexed neural activities recording across distant regions in the deep rodent brains. Coupling with optogenetic neural stimulation, the unique capabilities of this platform in electrophysiological readouts of projection dynamics in vivo are also demonstrated. The ability of these miniaturized, remotely controllable, and biocompatible ferromagnetic flexible electronics to afford minimally invasive manipulations in the soft tissues of the mammalian brain foreshadows applications in other organ systems, with great potential for broad utility in biomedical science and engineering.

Large-scale multimodal surface neural interfaces for primates

Deciphering the function of neural circuits can help with the understanding of brain function and treating neurological disorders. Progress toward this goal relies on the development of chronically stable neural interfaces capable of recording and modulating neural circuits with high spatial and temporal precision across large areas of the brain. Advanced innovations in designing high-density neural interfaces for small animal models have enabled breakthrough discoveries in neuroscience research. Developing similar neurotechnology for larger animal models such as nonhuman primates (NHPs) is critical to gain significant insights for translation to humans, yet still it remains elusive due to the challenges in design, fabrication, and system-level integration of such devices. This review focuses on implantable surface neural interfaces with electrical and optical functionalities with emphasis on the required technological features to realize scalable multimodal and chronically stable implants to address the unique challenges associated with nonhuman primate studies.

Concurrent behavioral and electrophysiological longitudinal recordings for in vivo assessment of aging

Electrophysiological and behavioral alterations, including sleep and cognitive impairments, are critical components of age-related decline and neurodegenerative diseases. In preclinical investigation, many refined techniques are employed to probe these phenotypes, but they are often conducted separately. Herein, we provide a protocol for one-time surgical implantation of EMG wires in the nuchal muscle and a skull-surface EEG headcap in mice, capable of 9-to-12-month recording longevity. All data acquisitions are wireless, making them compatible with simultaneous EEG recording coupled to multiple behavioral tasks, as we demonstrate with locomotion/sleep staging during home-cage video assessments, cognitive testing in the Barnes maze, and sleep disruption. Time-course EEG and EMG data can be accurately mapped to the behavioral phenotype and synchronized with neuronal frequencies for movement and the location to target in the Barnes maze. We discuss critical steps for optimizing headcap surgery and alternative approaches, including increasing the number of EEG channels or utilizing depth electrodes with the system. Combining electrophysiological and behavioral measurements in preclinical models of aging and neurodegeneration has great potential for improving mechanistic and therapeutic assessments and determining early markers of brain disorders.

Functional Two-Dimensional Materials for Bioelectronic Neural Interfacing

Realizing the neurological information processing by analyzing the complex data transferring behavior of populations and individual neurons is one of the fast-growing fields of neuroscience and bioelectronic technologies. This field is anticipated to cover a wide range of advanced applications, including neural dynamic monitoring, understanding the neurological disorders, human brain-machine communications and even ambitious mind-controlled prosthetic implant systems. To fulfill the requirements of high spatial and temporal resolution recording of neural activities, electrical, optical and biosensing technologies are combined to develop multifunctional bioelectronic and neuro-signal probes. Advanced two-dimensional (2D) layered materials such as graphene, graphene oxide, transition metal dichalcogenides and MXenes with their atomic-layer thickness and multifunctional capabilities show bio-stimulation and multiple sensing properties. These characteristics are beneficial factors for development of ultrathin-film electrodes for flexible neural interfacing with minimum invasive chronic interfaces to the brain cells and cortex. The combination of incredible properties of 2D nanostructure places them in a unique position, as the main materials of choice, for multifunctional reception of neural activities. The current review highlights the recent achievements in 2D-based bioelectronic systems for monitoring of biophysiological indicators and biosignals at neural interfaces.

Amelioration of ethanol-induced gastric ulcer in rats by quercetin: implication of Nrf2/HO1 and HMGB1/TLR4/NF-κB pathways

Gastric ulcer is a serious medical condition that can be developed due to an imbalance in the protective and destructive factors of the gastric system. Available therapies do not provide definite cure, thus, there is an urge to seek for alternative treatments. Quercetin is a natural flavonoid that possesses antioxidant and anti-inflammatory properties. In the current study, the antiulcerogenic effect of quercetin in ethanol-induced gastric ulcer (EI-GU) rat model was compared to Antodine® (a reference drug), to elucidate the potential underlying mechanisms. Quercetin (50 mg/kg) and Antodine® (20 mg/kg) were given orally for one week post ulcer induction by ethanol. EI-GU was associated with downregulation of SOD, CAT, Nrf2 and HO1, and accompanied by upregulation of inflammatory markers (i.e., HMGB1, NF-κB and TNFα) and an increase in Bax/Bcl2 ratio. Administration of quercetin resulted in a significant reduction in gastric volume in the stomach of ulcerative rats by 86% and a significant decrease in gastric lesion count by 3.5- folds, as compared with the ulcerative rats. Moreover, rats treated with quercetin showed upregulation of Nrf2 by 3.3-fold change and in HO1 by 3.5-fold change when compared to ulcerated rats, and decreased HMGB1, TLR4, NF-κB p65 and TNF-α by 50%, 53%, 52.9% and 54.9%, respectively. Treatment of rats with quercetin reduced Bax and Bax/Bcl2 ratio and increased Bcl2 relative to ulcerated rats. Thus, it can be concluded that the ulcerogenic curative properties of quercetin were mediated by antioxidant, anti-inflammatory and antiapoptotic activities.

3D CNT/MXene microspheres for combined photothermal/photodynamic/chemo for cancer treatment

MXene nanosheets have shown exciting potential in nanomedicine because of their large surface area, intense near-infrared (NIR) absorbance, and good biocompatibility. However, their development in the direction of treating tumors is constrained by the limitations of existing design methodologies. These methodologies lack control over the size and distribution of tumors. Moreover, their photodynamic therapy (PDT) effect is poor. To address this unmet medical need, a simple strategy that processes MXene with carbon nanotube (CNT) into a three-dimensional (3D) honeycomb structure having anti aggregation capacity was established. The structure can be used in disease phototherapy against tumors, bacteria, and viruses, such as photothermal therapy (PTT), photodynamic therapy (PDT), and multimodal synergistic therapy. In the present study, 3D CNT/MXene microspheres were obtained by the template method and spray-drying method. The microspheres possessed special photothermal effects and photothermal stability under NIR laser irradiation. Furthermore, the developed microspheres could achieve a maximum of 85.6% drug loading capability of doxorubicin (DOX). Under light irradiation at 650 and 808 nm, 3D CNT/MXene microspheres could efficiently produce singlet oxygen due to the effectiveness of CNTs as carries for Titanium Dioxide (TiO₂) photosensitizers present on the MXene surface. Furthermore, in vitro studies had showed that 3D CNT/MXene-DOX effectively inhibited the proliferation of HeLa cells. Hence, this study provides a promising platform for future clinical applications to realize PTT/PDT/chemotherapy combination cancer treatment based on MXene.

Nature of the Electrical Double Layer on Suspended Graphene Electrodes

The structure of interfacial water near suspended graphene electrodes in contact with aqueous solutions of Na₂SO₄, NH₄Cl, and (NH₄)₂SO₄ has been studied using confocal Raman spectroscopy, sum frequency vibrational spectroscopy, and Kelvin probe force microscopy. SO₄^2– anions were found to preferentially accumulate near the interface at an open circuit potential (OCP), creating an electrical field that orients water molecules below the interface, as revealed by the increased intensity of the O–H stretching peak of H-bonded water. No such increase is observed with NH₄Cl at the OCP. The intensity of the dangling O–H bond stretching peak however remains largely unchanged. The degree of orientation of the water molecules as well as the electrical double layer strength increased further when positive voltages are applied. Negative voltages on the other hand produced only small changes in the intensity of the H-bonded water peaks but affected the intensity and frequency of dangling O–H bond peaks. The TOC figure is an oversimplified representation of the system in this work.

A High-Performance Electrode Based on van der Waals Heterostructure for Neural Recording

Neural electrodes have been widely used to monitor neurological disorders and have a major impact on neuroscience, whereas traditional electrodes are limited to their inherent high impedance, which makes them insensitive to weak signals during recording neural signals. Herein, we developed a neural electrode based on the graphene/Ag van der Waals heterostructure for improving the detection sensitivity and signal-to-noise ratio (SNR). The impedance of the graphene/Ag electrode is reduced to 161.4 ± 13.4 MΩ μm², while the cathode charge-storage capacity (CSCc) reaches 24.2 ± 1.9 mC cm^-2, which is 6.3 and 48.4 times higher than those of the commercial Ag electrodes, respectively. Density functional theory (DFT) results find that the Ag-graphene interface has more doped electronic states, providing faster electron transfer and enhanced interfacial transport. In vivo detection sensitivity and SNR of graphene/Ag electrodes are significantly improved. The current work provides a feasible solution for designing brain electrodes to monitor neural signals more sensitively and accurately.

Biofunctionalization of Graphene-Based FET Sensors through Heterobifunctional Nanoscaffolds: Technology Validation toward Rapid COVID-19 Diagnostics and Monitoring

The biofunctionalization of graphene field-effect transistors (GFETs) through vinylsulfonated-polyethyleneimine nanoscaffold is presented for enhanced biosensing of severe acute respiratory-related coronavirus 2 (SARS-CoV-2) spike protein and human ferritin, two targets of great importance for the rapid diagnostic and monitoring of individuals with COVID-19. The heterobifunctional nanoscaffold enables covalent immobilization of binding proteins and antifouling polymers while the whole architecture is attached to graphene by multivalent π-π interactions. First, to optimize the sensing platform, concanavalin A is employed for glycoprotein detection. Then, monoclonal antibodies specific against SARS-CoV-2 spike protein and human ferritin are anchored, yielding biosensors with limit of detections of 0.74 and 0.23 nm, and apparent affinity constants (K D G F E T ) of 6.7 and 8.8 nm, respectively. Both biosensing platforms show good specificity, fast time response, and wide dynamic range (0.1-100 nm). Moreover, SARS-CoV-2 spike protein is also detected in spiked nasopharyngeal swab samples. To rigorously validate this biosensing technology, the GFET response is matched with surface plasmon resonance measurements, exhibiting linear correlations (from 2 to 100 ng cm-2) and good agreement in terms of K D values. Finally, the performance of the biosensors fabricated through the nanoscaffold strategy is compared with those obtained through the widely employed monopyrene approach, showing enhanced sensitivity.

Two-Dimensional Field-Effect Transistor Sensors: The Road toward Commercialization

The evolutionary success in information technology has been sustained by the rapid growth of sensor technology. Recently, advances in sensor technology have promoted the ambitious requirement to build intelligent systems that can be controlled by external stimuli along with independent operation, adaptivity, and low energy expenditure. Among various sensing techniques, field-effect transistors (FETs) with channels made of two-dimensional (2D) materials attract increasing attention for advantages such as label-free detection, fast response, easy operation, and capability of integration. With atomic thickness, 2D materials restrict the carrier flow within the material surface and expose it directly to the external environment, leading to efficient signal acquisition and conversion. This review summarizes the latest advances of 2D-materials-based FET (2D FET) sensors in a comprehensive manner that contains the material, operating principles, fabrication technologies, proof-of-concept applications, and prototypes. First, a brief description of the background and fundamentals is provided. The subsequent contents summarize physical, chemical, and biological 2D FET sensors and their applications. Then, we highlight the challenges of their commercialization and discuss corresponding solution techniques. The following section presents a systematic survey of recent progress in developing commercial prototypes. Lastly, we summarize the long-standing efforts and prospective future development of 2D FET-based sensing systems toward commercialization.

Graphene Oxide and Biomolecules for the Production of Functional 3D Graphene-Based Materials

Graphene and its derivatives have been widely employed in the manufacturing of novel composite nanomaterials which find applications across the fields of physics, chemistry, engineering and medicine. There are many techniques and strategies employed for the production, functionalization, and assembly of graphene with other organic and inorganic components. These are characterized by advantages and disadvantages related to the nature of the specific components involved. Among many, biomolecules and biopolymers have been extensively studied and employed during the last decade as building blocks, leading to the realization of graphene-based biomaterials owning unique properties and functionalities. In particular, biomolecules like nucleic acids, proteins and enzymes, as well as viruses, are of particular interest due to their natural ability to self-assemble via non-covalent interactions forming extremely complex and dynamic functional structures. The capability of proteins and nucleic acids to bind specific targets with very high selectivity or the ability of enzymes to catalyse specific reactions, make these biomolecules the perfect candidates to be combined with graphenes, and in particular graphene oxide, to create novel 3D nanostructured functional biomaterials. Furthermore, besides the ease of interaction between graphene oxide and biomolecules, the latter can be produced in bulk, favouring the scalability of the resulting nanostructured composite materials. Moreover, due to the presence of biological components, graphene oxide-based biomaterials are more environmentally friendly and can be manufactured more sustainably compared to other graphene-based materials assembled with synthetic and inorganic components. This review aims to provide an overview of the state of the art of 3D graphene-based materials assembled using graphene oxide and biomolecules, for the fabrication of novel functional and scalable materials and devices.

Full-bandwidth electrophysiology of seizures and epileptiform activity enabled by flexible graphene microtransistor depth neural probes

Mapping the entire frequency bandwidth of brain electrophysiological signals is of paramount importance for understanding physiological and pathological states. The ability to record simultaneously DC-shifts, infraslow oscillations (<0.1 Hz), typical local field potentials (0.1-80 Hz) and higher frequencies (80-600 Hz) using the same recording site would particularly benefit preclinical epilepsy research and could provide clinical biomarkers for improved seizure onset zone delineation. However, commonly used metal microelectrode technology suffers from instabilities that hamper the high fidelity of DC-coupled recordings, which are needed to access signals of very low frequency. In this study we used flexible graphene depth neural probes (gDNPs), consisting of a linear array of graphene microtransistors, to concurrently record DC-shifts and high-frequency neuronal activity in awake rodents. We show here that gDNPs can reliably record and map with high spatial resolution seizures, pre-ictal DC-shifts and seizure-associated spreading depolarizations together with higher frequencies through the cortical laminae to the hippocampus in a mouse model of chemically induced seizures. Moreover, we demonstrate the functionality of chronically implanted devices over 10 weeks by recording with high fidelity spontaneous spike-wave discharges and associated infraslow oscillations in a rat model of absence epilepsy. Altogether, our work highlights the suitability of this technology for in vivo electrophysiology research, and in particular epilepsy research, by allowing stable and chronic DC-coupled recordings.

Non-invasive on-skin sensors for brain machine interfaces with epitaxial graphene

Objective. Brain-machine interfaces are key components for the development of hands-free, brain-controlled devices. Electroencephalogram (EEG) electrodes are particularly attractive for harvesting the neural signals in a non-invasive fashion.Approach.Here, we explore the use of epitaxial graphene (EG) grown on silicon carbide on silicon for detecting the EEG signals with high sensitivity.Main results and significance.This dry and non-invasive approach exhibits a markedly improved skin contact impedance when benchmarked to commercial dry electrodes, as well as superior robustness, allowing prolonged and repeated use also in a highly saline environment. In addition, we report the newly observed phenomenon of surface conditioning of the EG electrodes. The prolonged contact of the EG with the skin electrolytes functionalize the grain boundaries of the graphene, leading to the formation of a thin surface film of water through physisorption and consequently reducing its contact impedance more than three-fold. This effect is primed in highly saline environments, and could be also further tailored as pre-conditioning to enhance the performance and reliability of the EG sensors.

Recent advances in recording and modulation technologies for next-generation neural interfaces

Along with the advancement in neural engineering techniques, unprecedented progress in the development of neural interfaces has been made over the past few decades. However, despite these achievements, there is still room for further improvements especially toward the possibility of monitoring and modulating neural activities with high resolution and specificity in our daily lives. In an effort of taking a step toward the next-generation neural interfaces, we want to highlight the recent progress in neural technologies. We will cover a wide scope of such developments ranging from novel platforms for highly specific recording and modulation to system integration for practical applications of novel interfaces.

Graphene and graphene-related materials as brain electrodes

Neural electrodes are used for acquiring neuron signals in brain-machine interfaces, and they are crucial for next-generation neuron engineering and related medical applications. Thus, developing flexible, stable and high-resolution neural electrodes will play an important role in stimulation, acquisition, recording and analysis of signals. Compared with traditional metallic electrodes, electrodes based on graphene and other two-dimensional materials have attracted wide attention in electrophysiological recording and stimulation due to their excellent physical properties such as unique flexibility, low resistance, and high optical transparency. In this review, we have reviewed the recent progress of electrodes based on graphene, graphene/polymer compounds and graphene-related materials for neuron signal recording, stimulation, and related optical signal coupling technology, which provides an outlook on the role of electrodes in the nanotechnology-neuron interface as well as medical diagnosis.

Assessment of Brain Functional Activity Using a Miniaturized Head-Mounted Scanning Photoacoustic Imaging System in Awake and Freely Moving Rats

Understanding the relationship between brain function and natural behavior remains a significant challenge in neuroscience because there are very few convincing imaging/recording tools available for the evaluation of awake and freely moving animals. Here, we employed a miniaturized head-mounted scanning photoacoustic imaging (hmPAI) system to image real-time cortical dynamics. A compact photoacoustic (PA) probe based on four in-house optical fiber pads and a single custom-made 48-MHz focused ultrasound transducer was designed to enable focused dark-field PA imaging, and miniature linear motors were included to enable two-dimensional (2D) scanning. The total dimensions and weight of the proposed hmPAI system are only approximately 50 × 64 × 48 mm and 58.7 g (excluding cables). Our ex vivo phantom experimental tests revealed that a spatial resolution of approximately 0.225 mm could be achieved at a depth of 9 mm. Our in vivo results further revealed that the diameters of cortical vessels draining into the superior sagittal sinus (SSS) could be clearly imaged and continuously observed in both anesthetized rats and awake, freely moving rats. Statistical analysis showed that the full width at half maximum (FWHM) of the PA A-line signals (relative to the blood vessel diameter) was significantly increased in the selected SSS-drained cortical vessels of awake rats (0.58 ± 0.17 mm) compared with those of anesthetized rats (0.31 ± 0.09 mm) (p < 0.01, paired t-test). In addition, the number of pixels in PA B-scan images (relative to the cerebral blood volume (CBV)) was also significantly increased in the selected SSS-drained blood vessels of awake rats (107.66 ± 23.02 pixels) compared with those of anesthetized rats (81.99 ± 21.52 pixels) (p < 0.01, paired t-test). This outcome may result from a more active brain in awake rats than in anesthetized rats, which caused cerebral blood vessels to transport more blood to meet the increased nutrient demand of the tissue, resulting in an obvious increase in blood vessel volume. This hmPAI system was further validated for utility in the brains of awake and freely moving rats, showing that their natural behavior was unimpaired during vascular imaging, thereby providing novel opportunities for studies of behavior, cognition, and preclinical models of brain diseases.

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.

Morphology and Chemical Purity of Water Suspension of Graphene Oxide FLAKES Aged for 14 Months in Ambient Conditions. A Preliminary Study

Graphene and its derivatives have attracted scientists’ interest due to their exceptional properties, making them alluring candidates for multiple applications. However, still little is known about the properties of as-obtained graphene derivatives during long-term storage. The aim of this study was to check whether or not 14 months of storage time impacts graphene oxide flakes’ suspension purity. Complementary micro and nanoscale characterization techniques (SEM, AFM, EDS, FTIR, Raman spectroscopy, and elemental combustion analysis) were implemented for a detailed description of the topography and chemical properties of graphene oxide flakes. The final step was pH evaluation of as-obtained and aged samples. Our findings show that purified flakes sustained their purity over 14 months of storage.