Semiconductor nanorod-carbon nanotube biomimetic films for wire-free photostimulation of blind retinas

Photoreceptor-Mimetic Microflowers for Restoring Light Responses in Degenerative Retina through a 2D Nanopetal/Cell Biointerface

Retinitis pigmentosa is the main cause of inherited human blindness and is associated with dysfunctional photoreceptors (PRs). Compared with traditional methods, optoelectronic stimulation can better preserve the structural integrity and genetic content of the retina. However, enhancing the spatiotemporal accuracy of stimulation is challenging. Quantum dot-doped ZnIn2S4 microflowers (MF) are utilized to construct a biomimetic photoelectric interface with a 0D/3D heterostructure, aiming to restore the light response in PR-degenerative mice. The MF bio interface has dimensions similar to those of natural PRs and can be distributed within the curved spatial region of the retina, mimicking cellular dispersion. The soft 2D nano petals of the MF provide a large specific surface area for photoelectric activation and simulate the flexibility interfacing between cells. This bio interface can selectively restore the light responses of seven types of retina ganglion cells that encode brightness. The distribution of responsive cells forms a pattern similar to that of normal mice, which may reflect the generation of the initial "neural code" in the degenerative retina. Patch-clamp recordings indicate that the bio interface can induce spiking and postsynaptic currents at the single-neuron level. The results will shed light on the development of a potential bionic subretinal prosthetic toolkit for visual function restoration.

Capacitive and Efficient Near-Infrared Stimulation of Neurons via an Ultrathin AgBiS2 Nanocrystal Layer

Colloidal nanocrystals (NCs) exhibit significant potential for photovoltaic bioelectronic interfaces because of their solution processability, tunable energy levels, and inorganic nature, lending them chemical stability. Silver bismuth sulfide (AgBiS2) NCs, free from toxic heavy-metal elements (e.g., Cd, Hg, and Pb), particularly offer an exceptional absorption coefficient exceeding 105 cm-1 in the near-infrared (NIR), surpassing many of their inorganic counterparts. Here, we integrated an ultrathin (24 nm) AgBiS2 NC layer into a water-stable photovoltaic bioelectronic device architecture that showed a high capacitive photocurrent of 2.3 mA·cm-2 in artificial cerebrospinal fluid (aCSF) and ionic charges over 10 μC·cm-2 at a low NIR intensity of 0.5 mW·mm-2. The device without encapsulation showed a halftime of 12.5 years under passive accelerated aging test and did not show any toxicity on neurons. Furthermore, patch-clamp electrophysiology on primary hippocampal neurons under whole-cell configuration revealed that the device elicited neuron firing at intensity levels more than an order of magnitude below the established ocular safety limits. These findings point to the potential of AgBiS2 NCs for photovoltaic retinal prostheses.

Soft Bioelectronics Using Nanomaterials and Nanostructures for Neuroengineering

The identification of neural networks for large areas and the regulation of neuronal activity at the single-neuron scale have garnered considerable attention in neuroscience. In addition, detecting biochemical molecules and electrically, optically, and chemically controlling neural functions are key research issues. However, conventional rigid and bulky bioelectronics face challenges for neural applications, including mechanical mismatch, unsatisfactory signal-to-noise ratio, and poor integration of multifunctional components, thereby degrading the sensing and modulation performance, long-term stability and biocompatibility, and diagnosis and therapy efficacy. Implantable bioelectronics have been developed to be mechanically compatible with the brain environment by adopting advanced geometric designs and utilizing intrinsically stretchable materials, but such advances have not been able to address all of the aforementioned challenges.Recently, the exploration of nanomaterial synthesis and nanoscale fabrication strategies has facilitated the design of unconventional soft bioelectronics with mechanical properties similar to those of neural tissues and submicrometer-scale resolution comparable to typical neuron sizes. The introduction of nanotechnology has provided bioelectronics with improved spatial resolution, selectivity, single neuron targeting, and even multifunctionality. As a result, this state-of-the-art nanotechnology has been integrated with bioelectronics in two main types, i.e., bioelectronics integrated with synthesized nanomaterials and bioelectronics with nanoscale structures. The functional nanomaterials can be synthesized and assembled to compose bioelectronics, allowing easy customization of their functionality to meet specific requirements. The unique nanoscale structures implemented with the bioelectronics could maximize the performance in terms of sensing and stimulation. Such soft nanobioelectronics have demonstrated their applicability for neuronal recording and modulation over a long period at the intracellular level and incorporation of multiple functions, such as electrical, optical, and chemical sensing and stimulation functions.In this Account, we will discuss the technical pathways in soft bioelectronics integrated with nanomaterials and implementing nanostructures for application to neuroengineering. We traced the historical development of bioelectronics from rigid and bulky structures to soft and deformable devices to conform to neuroengineering requirements. Recent approaches that introduced nanotechnology into neural devices enhanced the spatiotemporal resolution and endowed various device functions. These soft nanobioelectronic technologies are discussed in two categories: bioelectronics with synthesized nanomaterials and bioelectronics with nanoscale structures. We describe nanomaterial-integrated soft bioelectronics exhibiting various functionalities and modalities depending on the integrated nanomaterials. Meanwhile, soft bioelectronics with nanoscale structures are explained with their superior resolution and unique administration methods. We also exemplified the neural sensing and stimulation applications of soft nanobioelectronics across various modalities, showcasing their clinical applications in the treatment of neurological diseases, such as brain tumors, epilepsy, and Parkinson's disease. Finally, we discussed the challenges and direction of next-generation technologies.

Nanoparticle-based optical interfaces for retinal neuromodulation: a review

Degeneration of photoreceptors in the retina is a leading cause of blindness, but commonly leaves the retinal ganglion cells (RGCs) and/or bipolar cells extant. Consequently, these cells are an attractive target for the invasive electrical implants colloquially known as "bionic eyes." However, after more than two decades of concerted effort, interfaces based on conventional electrical stimulation approaches have delivered limited efficacy, primarily due to the current spread in retinal tissue, which precludes high-acuity vision. The ideal prosthetic solution would be less invasive, provide single-cell resolution and an ability to differentiate between different cell types. Nanoparticle-mediated approaches can address some of these requirements, with particular attention being directed at light-sensitive nanoparticles that can be accessed via the intrinsic optics of the eye. Here we survey the available known nanoparticle-based optical transduction mechanisms that can be exploited for neuromodulation. We review the rapid progress in the field, together with outstanding challenges that must be addressed to translate these techniques to clinical practice. In particular, successful translation will likely require efficient delivery of nanoparticles to stable and precisely defined locations in the retinal tissues. Therefore, we also emphasize the current literature relating to the pharmacokinetics of nanoparticles in the eye. While considerable challenges remain to be overcome, progress to date shows great potential for nanoparticle-based interfaces to revolutionize the field of visual prostheses.

Application of Nanoscopic Quantum Systems in Retinal Restoration

This is an Editorial and does not have an abstract. Please download the PDF or view the article in HTML.

Colloidal self-assembly of soft neural interfaces from injectable photovoltaic microdevices

Biomimetic retinas with a wide field of view and high resolution are in demand for neuroprosthetics and robot vision. Conventional neural prostheses are manufactured outside the application area and implanted as a complete device using invasive surgery. Here, a minimally invasive strategy based on in situ self-assembly of photovoltaic microdevices (PVMs) is presented. The photoelectricity transduced by PVMs upon visible light illumination reaches the intensity levels that could effectively activate the retinal ganglion cell layers. The geometry and multilayered architecture of the PVMs along with the tunability of their physical properties such as size and stiffness allow several routes for initiating a self-assembly process. The spatial distribution and packing density of the PVMs within the assembled device are modulated through concentration, liquid discharge speed, and coordinated self-assembly steps. Subsequent injection of a photocurable and transparent polymer facilitates tissue integration and reinforces the cohesion of the device. Taken together, the presented methodology introduces three unique features: minimally invasive implantation, personalized visual field and acuity, and a device geometry adaptable to retina topography.

Physical mechanisms of emerging neuromodulation modalities

One of the ultimate goals of neurostimulation field is to design materials, devices and systems that can simultaneously achieve safe, effective and tether-free operation. For that, understanding the working mechanisms and potential applicability of neurostimulation techniques is important to develop noninvasive, enhanced, and multi-modal control of neural activity. Here, we review direct and transduction-based neurostimulation techniques by discussing their interaction mechanisms with neurons via electrical, mechanical, and thermal means. We show how each technique targets modulation of specific ion channels (e.g. voltage-gated, mechanosensitive, heat-sensitive) by exploiting fundamental wave properties (e.g. interference) or engineering nanomaterial-based systems for efficient energy transduction. Overall, our review provides a detailed mechanistic understanding of neurostimulation techniques together with their applications toin vitro, in vivo, and translational studies to guide the researchers toward developing more advanced systems in terms of noninvasiveness, spatiotemporal resolution, and clinical applicability.

Light-triggered cardiac microphysiological model

Light is recognized as an accurate and noninvasive tool for stimulating excitable cells. Here, we report on a non-genetic approach based on organic molecular phototransducers that allows wiring- and electrode-free tissue modulation. As a proof of concept, we show photostimulation of an in vitro cardiac microphysiological model mediated by an amphiphilic azobenzene compound that preferentially dwells in the cell membrane. Exploiting this optical based stimulation technology could be a disruptive approach for highly resolved cardiac tissue stimulation.

Engineering optical tools for remotely controlled brain stimulation and regeneration

Neurological disorders are one of the world's leading medical and societal challenges due to the lack of efficacy of the first line treatment. Although pharmacological and non-pharmacological interventions have been employed with the aim of regulating neuronal activity and survival, they have failed to avoid symptom relapse and disease progression in the vast majority of patients. In the last 5 years, advanced drug delivery systems delivering bioactive molecules and neuromodulation strategies have been developed to promote tissue regeneration and remodel neuronal circuitry. However, both approaches still have limited spatial and temporal precision over the desired target regions. While external stimuli such as electromagnetic fields and ultrasound have been employed in the clinic for non-invasive neuromodulation, they do not have the capability of offering single-cell spatial resolution as light stimulation. Herein, we review the latest progress in this area of study and discuss the prospects of using light-responsive nanomaterials to achieve on-demand delivery of drugs and neuromodulation, with the aim of achieving brain stimulation and regeneration.

Design Optimization and Characterization with Fabrication of Nanomaterials-Based Photo Diode Cell for Subretinal Implant Application

An ultrathin nano photodiode array fabricated in a flexible substrate can be an ideal therapeutic replacement for degenerated photoreceptor cells damaged by Age-related Macula Degeneration (AMD) and Retinitis Pigmentosa (RP), such as retinal infections. Silicon-based photodiode arrays have been attempted as artificial retinas. Considering the difficulties caused by hard silicon subretinal implants, researchers have diverted their attention towards organic photovoltaic cells-based subretinal implants. Indium-Tin Oxide (ITO) has been a favorite choice as an anode electrode. A mix of poly(3-hexylthiophene) and [6,6]-phenyl C61-butyric acid methyleste (P3HT: PCBM) has been utilized as an active layer in such nanomaterial-based subretinal implants. Though encouraging results have been obtained during the trial of such retinal implants, the need to replace ITO with a suitable transparent conductive electrode will be a suitable substitute. Further, conjugated polymers have been used as active layers in such photodiodes and have shown delamination in the retinal space over time despite their biocompatibility. This research attempted to fabricate and characterize Bulk Hetero Junction (BHJ) based Nano Photo Diode (NPD) utilizing Graphene-polyethylene terephthalate (G-PET)/semiconducting Single-Wall Carbon Nano Tubes (s-SWCNT): fullerene (C₆₀) blend/aluminium (Al) structure to determine the issues in the development of subretinal prosthesis. An effective design approach adopted in this analysis has resulted in developing an NPD with an Efficiency of 10.1% in a non-ITO-driven NPD structure. Additionally, the results show that the efficiency can be further improved by increasing active layer thickness.

Semiconducting electrodes for neural interfacing: a review

In the past 50 years, the advent of electronic technology to directly interface with neural tissue has transformed the fields of medicine and biology. Devices that restore or even replace impaired bodily functions, such as deep brain stimulators and cochlear implants, have ushered in a new treatment era for previously intractable conditions. Meanwhile, electrodes for recording and stimulating neural activity have allowed researchers to unravel the vast complexities of the human nervous system. Recent advances in semiconducting materials have allowed effective interfaces between electrodes and neuronal tissue through novel devices and structures. Often these are unattainable using conventional metallic electrodes. These have translated into advances in research and treatment. The development of semiconducting materials opens new avenues in neural interfacing. This review considers this emerging class of electrodes and how it can facilitate electrical, optical, and chemical sensing and modulation with high spatial and temporal precision. Semiconducting electrodes have advanced electrically based neural interfacing technologies owing to their unique electrochemical and photo-electrochemical attributes. Key operation modalities, namely sensing and stimulation in electrical, biochemical, and optical domains, are discussed, highlighting their contrast to metallic electrodes from the application and characterization perspective.

Nanocomposite Hydrogels as Functional Extracellular Matrices

Over recent years, nano-engineered materials have become an important component of artificial extracellular matrices. On one hand, these materials enable static enhancement of the bulk properties of cell scaffolds, for instance, they can alter mechanical properties or electrical conductivity, in order to better mimic the in vivo cell environment. Yet, many nanomaterials also exhibit dynamic, remotely tunable optical, electrical, magnetic, or acoustic properties, and therefore, can be used to non-invasively deliver localized, dynamic stimuli to cells cultured in artificial ECMs in three dimensions. Vice versa, the same, functional nanomaterials, can also report changing environmental conditions-whether or not, as a result of a dynamically applied stimulus-and as such provide means for wireless, long-term monitoring of the cell status inside the culture. In this review article, we present an overview of the technological advances regarding the incorporation of functional nanomaterials in artificial extracellular matrices, highlighting both passive and dynamically tunable nano-engineered components.

Photoactive Nanomaterials for Wireless Neural Biomimetics, Stimulation, and Regeneration

Nanomaterials at the neural interface can provide the bridge between bioelectronic devices and native neural tissues and achieve bidirectional transmission of signals with our brain. Photoactive nanomaterials, such as inorganic and polymeric nanoparticles, nanotubes, nanowires, nanorods, nanosheets or related, are being explored to mimic, modulate, control, or even substitute the functions of neural cells or tissues. They show great promise in next generation technologies for the neural interface with excellent spatial and temporal accuracy. In this review, we highlight the discovery and understanding of these nanomaterials in precise control of an individual neuron, biomimetic retinal prosthetics for vision restoration, repair or regeneration of central or peripheral neural tissues, and wireless deep brain stimulation for treatment of movement or mental disorders. The most intriguing feature is that the photoactive materials fit within a minimally invasive and wireless strategy to trigger the flux of neurologically active molecules and thus influences the cell membrane potential or key signaling molecule related to gene expression. In particular, we focus on worthy pathways of photosignal transduction at the nanomaterial-neural interface and the behavior of the biological system. Finally, we describe the challenges on how to design photoactive nanomaterials specific to neurological disorders. There are also some open issues such as long-term interface stability and signal transduction efficiency to further explore for clinical practice.

Comparison of fractal and grid electrodes for studying the effects of spatial confinement on dissociated retinal neuronal and glial behavior

Understanding the impact of the geometry and material composition of electrodes on the survival and behavior of retinal cells is of importance for both fundamental cell studies and neuromodulation applications. We investigate how dissociated retinal cells from C57BL/6J mice interact with electrodes made of vertically-aligned carbon nanotubes grown on silicon dioxide substrates. We compare electrodes with different degrees of spatial confinement, specifically fractal and grid electrodes featuring connected and disconnected gaps between the electrodes, respectively. For both electrodes, we find that neuron processes predominantly accumulate on the electrode rather than the gap surfaces and that this behavior is strongest for the grid electrodes. However, the 'closed' character of the grid electrode gaps inhibits glia from covering the gap surfaces. This lack of glial coverage for the grids is expected to have long-term detrimental effects on neuronal survival and electrical activity. In contrast, the interconnected gaps within the fractal electrodes promote glial coverage. We describe the differing cell responses to the two electrodes and hypothesize that there is an optimal geometry that maximizes the positive response of both neurons and glia when interacting with electrodes.

Electrical Stimulation of Neurons with Quantum Dots via Near-Infrared Light

Photovoltaic biointerfaces offer wireless and battery-free bioelectronic medicine via photomodulation of neurons. Near-infrared (NIR) light enables communication with neurons inside the deep tissue and application of high photon flux within the ocular safety limit of light exposure. For that, nonsilicon biointerfaces are highly demanded for thin and flexible operation. Here, we devised a flexible quantum dot (QD)-based photovoltaic biointerface that stimulates cells within the spectral tissue transparency window by using NIR light (λ = 780 nm). Integration of an ultrathin QD layer of 25 nm into a multilayered photovoltaic architecture enables transduction of NIR light to safe capacitive ionic currents that leads to reproducible action potentials on primary hippocampal neurons with high success rates. The biointerfaces exhibit low in vitro toxicity and robust photoelectrical performance under different stability tests. Our findings show that colloidal quantum dots can be used in wireless bioelectronic medicine for brain, heart, and retina.

Optoelectronic Neural Interfaces Based on Quantum Dots

Optoelectronic modulation of neural activity is an emerging field for the investigation of neural circuits and the development of neural therapeutics. Among a wide variety of nanomaterials, colloidal quantum dots provide unique optoelectronic features for neural interfaces such as sensitive tuning of electron and hole energy levels via the quantum confinement effect, controlling the carrier localization via band alignment, and engineering the surface by shell growth and ligand engineering. Even though colloidal quantum dots have been frontier nanomaterials for solar energy harvesting and lighting, their application to optoelectronic neural interfaces has remained below their significant potential. However, this potential has recently gained attention with the rise of bioelectronic medicine. In this review, we unravel the fundamentals of quantum-dot-based optoelectronic biointerfaces and discuss their neuromodulation mechanisms starting from the quantum dot level up to electrode-electrolyte interactions and stimulation of neurons with their physiological pathways. We conclude the review by proposing new strategies and possible perspectives toward nanodevices for the optoelectronic stimulation of neural tissue by utilizing the exceptional nanoscale properties of colloidal quantum dots.

Controlled assembly of retinal cells on fractal and Euclidean electrodes

Controlled assembly of retinal cells on artificial surfaces is important for fundamental cell research and medical applications. We investigate fractal electrodes with branches of vertically-aligned carbon nanotubes and silicon dioxide gaps between the branches that form repeating patterns spanning from micro- to milli-meters, along with single-scaled Euclidean electrodes. Fluorescence and electron microscopy show neurons adhere in large numbers to branches while glial cells cover the gaps. This ensures neurons will be close to the electrodes’ stimulating electric fields in applications. Furthermore, glia won’t hinder neuron-branch interactions but will be sufficiently close for neurons to benefit from the glia’s life-supporting functions. This cell ‘herding’ is adjusted using the fractal electrode’s dimension and number of repeating levels. We explain how this tuning facilitates substantial glial coverage in the gaps which fuels neural networks with small-world structural characteristics. The large branch-gap interface then allows these networks to connect to the neuron-rich branches.

Tissue-Like Optoelectronic Neural Interface Enabled by PEDOT:PSS Hydrogel for Cardiac and Neural Stimulation

Optoelectronic biointerfaces have made a significant impact on modern science and technology from understanding the mechanisms of the neurotransmission to the recovery of the vision for blinds. They are based on the cell interfaces made of organic or inorganic materials such as silicon, graphene, oxides, quantum dots, and π-conjugated polymers, which are dry and stiff unlike a cell/tissue environment. On the other side, wet and soft hydrogels have recently been started to attract significant attention for bioelectronics because of its high-level tissue-matching biomechanics and biocompatibility. However, it is challenging to obtain optimal opto-bioelectronic devices by using hydrogels requiring device, heterojunction, and hydrogel engineering. Here, an optoelectronic biointerface integrated with a poly(3,4-ethylenedioxythiophene):poly(styrene sulfonate), PEDOT:PSS, hydrogel that simultaneously achieves efficient, flexible, stable, biocompatible, and safe photostimulation of cells is demonstrated. Besides their interfacial tissue-like biomechanics, ≈34 kPa, and high-level biocompatibility, hydrogel-integration facilitates increase in charge injection amounts sevenfolds with an improved responsivity of 156 mA W^-1 , stability under mechanical bending , and functional lifetime over three years. Finally, these devices enable stimulation of individual hippocampal neurons and photocontrol of beating frequency of cardiac myocytes via safe charge-balanced capacitive currents. Therefore, hydrogel-enabled optoelectronic biointerfaces hold great promise for next-generation wireless neural and cardiac implants.

Soft Devices for High-Resolution Neuro-Stimulation: The Interplay Between Low-Rigidity and Resolution

The field of neurostimulation has evolved over the last few decades from a crude, low-resolution approach to a highly sophisticated methodology entailing the use of state-of-the-art technologies. Neurostimulation has been tested for a growing number of neurological applications, demonstrating great promise and attracting growing attention in both academia and industry. Despite tremendous progress, long-term stability of the implants, their large dimensions, their rigidity and the methods of their introduction and anchoring to sensitive neural tissue remain challenging. The purpose of this review is to provide a concise introduction to the field of high-resolution neurostimulation from a technological perspective and to focus on opportunities stemming from developments in materials sciences and engineering to reduce device rigidity while optimizing electrode small dimensions. We discuss how these factors may contribute to smaller, lighter, softer and higher electrode density devices.

Morphological Factors that Underlie Neural Sensitivity to Stimulation in the Retina

Retinal prostheses are a promising therapeutic intervention for patients afflicted by outer retinal degenerative diseases like retinitis pigmentosa and age-related macular degeneration. While significant advances in the development of retinal implants have been made, the quality of vision elicited by these devices remains largely sub-optimal. The variability in the responses produced by retinal devices is most likely due to the differences between the natural cell type-specific signaling that occur in the healthy retina vs. the non-specific activation of multiple cell types arising from artificial stimulation. In order to replicate these natural signaling patterns, stimulation strategies must be capable of preferentially activating specific RGC types. To design more selective stimulation strategies, a better understanding of the morphological factors that underlie the sensitivity to prosthetic stimulation must be developed. This review will focus on the role that different anatomical components play in driving the direct activation of RGCs by extracellular stimulation. Briefly, it will (1) characterize the variability in morphological properties of α-RGCs, (2) detail the influence of morphology on the direct activation of RGCs by electric stimulation, and (3) describe some of the potential biophysical mechanisms that could explain differences in activation thresholds and electrically evoked responses between RGC types.

Applications of Carbon Nanotubes in the Internet of Things Era

The post-Moore's era has boosted the progress in carbon nanotube-based transistors. Indeed, the 5G communication and cloud computing stimulate the research in applications of carbon nanotubes in electronic devices. In this perspective, we deliver the readers with the latest trends in carbon nanotube research, including high-frequency transistors, biomedical sensors and actuators, brain-machine interfaces, and flexible logic devices and energy storages. Future opportunities are given for calling on scientists and engineers into the emerging topics.

Carbon Nanotube Polymer Scaffolds as a Conductive Alternative for the Construction of Retinal Sheet Tissue

With the great success of graphene in the biomedical field, carbon nanotubes have attracted increasing attention for different applications in ophthalmology. Here, we report a novel retinal sheet composed of carbon nanotubes (CNTs) and poly(lactic-co-glycolic acid) (PLGA) that can enhance retinal cell therapy. By tuning our CNTs to regulate the mechanical characteristics of retina sheets, we were able to improve the in vitro viability of retinal ganglion cells derived from human-induced pluripotent stem cells incorporated into CNTs. Engrafted retinal ganglion cells displayed signs of regenerating processes along the optic nerve. Compared with PLGA scaffolds, CNT-PLGA retinal sheet tissue has excellent electrical conductivity, biocompatibility, and biodegradation. This new biomaterial offers new insight into retinal injury, repair, and regeneration.

Electrochemically Synthesized Poly(3-hexylthiophene) Nanowires as Photosensitive Neuronal Interfaces

Poly(3-hexylthiophene) (P3HT) is a hole-conducting polymer that has been intensively used to develop organic optoelectronic devices (e.g., organic solar cells). Recently, P3HT films and nanoparticles have also been used to restore the photosensitivity of retinal neurons. The template-assisted electrochemical synthesis of polymer nanowires advantageously combines polymerization and polymer nanostructuring into one, relatively simple, procedure. However, obtaining P3HT nanowires through this procedure was rarely investigated. Therefore, this study aimed to investigate the template-assisted electrochemical synthesis of P3HT nanowires doped with tetrabutylammonium hexafluorophosphate (TBAHFP) and their biocompatibility with primary neurons. We show that template-assisted electrochemical synthesis can relatively easily turn 3-hexylthiophene (3HT) into longer (e.g., 17 ± 3 µm) or shorter (e.g., 1.5 ± 0.4 µm) P3HT nanowires with an average diameter of 196 ± 55 nm (determined by the used template). The nanowires produce measurable photocurrents following illumination. Finally, we show that primary cortical neurons can be grown onto P3HT nanowires drop-casted on a glass substrate without relevant changes in their viability and electrophysiological properties, indicating that P3HT nanowires obtained by template-assisted electrochemical synthesis represent a promising neuronal interface for photostimulation.

Nanoengineering InP Quantum Dot-Based Photoactive Biointerfaces for Optical Control of Neurons

Light-activated biointerfaces provide a non-genetic route for effective control of neural activity. InP quantum dots (QDs) have a high potential for such biomedical applications due to their uniquely tunable electronic properties, photostability, toxic-heavy-metal-free content, heterostructuring, and solution-processing ability. However, the effect of QD nanostructure and biointerface architecture on the photoelectrical cellular interfacing remained unexplored. Here, we unravel the control of the photoelectrical response of InP QD-based biointerfaces via nanoengineering from QD to device-level. At QD level, thin ZnS shell growth (∼0.65 nm) enhances the current level of biointerfaces over an order of magnitude with respect to only InP core QDs. At device-level, band alignment engineering allows for the bidirectional photoelectrochemical current generation, which enables light-induced temporally precise and rapidly reversible action potential generation and hyperpolarization on primary hippocampal neurons. Our findings show that nanoengineering QD-based biointerfaces hold great promise for next-generation neurostimulation devices.

Quantum dot and electron acceptor nano-heterojunction for photo-induced capacitive charge-transfer

Capacitive charge transfer at the electrode/electrolyte interface is a biocompatible mechanism for the stimulation of neurons. Although quantum dots showed their potential for photostimulation device architectures, dominant photoelectrochemical charge transfer combined with heavy-metal content in such architectures hinders their safe use. In this study, we demonstrate heavy-metal-free quantum dot-based nano-heterojunction devices that generate capacitive photoresponse. For that, we formed a novel form of nano-heterojunctions using type-II InP/ZnO/ZnS core/shell/shell quantum dot as the donor and a fullerene derivative of PCBM as the electron acceptor. The reduced electron–hole wavefunction overlap of 0.52 due to type-II band alignment of the quantum dot and the passivation of the trap states indicated by the high photoluminescence quantum yield of 70% led to the domination of photoinduced capacitive charge transfer at an optimum donor–acceptor ratio. This study paves the way toward safe and efficient nanoengineered quantum dot-based next-generation photostimulation devices.

Smart nano-micro platforms for ophthalmological applications: The state-of-the-art and future perspectives

Smart nano-micro platforms have been extensively applied for diverse biomedical applications, mostly focusing on cancer therapy. In comparison with conventional nanotechnology, the smart nano-micro matrix can exhibit specific response to exogenous or endogenous triggers, and thus can achieve multiple functions e.g. site-specific drug delivery, bio-imaging and detection of bio-molecules. These intriguing techniques have expanded into ophthalmology in recent years, yet few works have been summarized in this field. In this work, we provide the state-of-the-art of diverse nano-micro platforms based on both the conventional materials (e.g. natural or synthetic polymers, lipid nanomaterials, metal and metal oxide nanoparticles) and emerging nanomaterials (e.g. up-conversion nanoparticles, quantum dots and carbon materials) in ophthalmology, with some smart nano/micro platformers highlighted. The common ocular diseases studied in the field of nano-micro systems are firstly introduced, and their therapeutic method and the related drawback in clinic treatment are presented. The recent progress of different materials for diverse ocular applications is then demonstrated, with the representative nano- and micro-systems highlighted in detail. At last, an in-depth discussion on the clinical translation challenges faced in this field and the future direction are provided. This review would allow the researchers to design more smart nanomedicines in a more rational manner for specific ophthalmology applications.

A Tale of Tails: Thermodynamics of CdSe Nanocrystal Surface Ligand Exchange

The surface ligands of semiconductor nanocrystals (NCs) are central for determining their properties and for their flexible implementation in diverse applications. Thus far, the thermodynamic characteristics of ligand exchange reactions were attained by indirect methods. Isothermal titration calorimetry is utilized to directly and independently measure both the equilibrium constant and the reaction enthalpy of a model ligand exchange reaction from oleate-capped CdSe NCs to a series of alkylthiols. Increased reaction exothermicity for longer chains, accompanied by a decrease in reaction entropy with an overall enthalpy-entropy compensation behavior is observed, explained by the length-dependent interchain interactions and the organization of the bound ligands on the NCs' surface. An increase in the spontaneity of the reaction with decreasing NC size is also revealed, due to their enhanced surface reactivity. This work provides a fundamental understanding of the physicochemical properties of the NC surface with implications for NC surface ligand design.

Retinal Prosthetic Approaches to Enhance Visual Perception for Blind Patients

Retinal prostheses are implantable devices that aim to restore the vision of blind patients suffering from retinal degeneration, mainly by artificially stimulating the remaining retinal neurons. Some retinal prostheses have successfully reached the stage of clinical trials; however, these devices can only restore vision partially and remain insufficient to enable patients to conduct everyday life independently. The visual acuity of the artificial vision is limited by various factors from both engineering and physiological perspectives. To overcome those issues and further enhance the visual resolution of retinal prostheses, a variety of retinal prosthetic approaches have been proposed, based on optimization of the geometries of electrode arrays and stimulation pulse parameters. Other retinal stimulation modalities such as optics, ultrasound, and magnetics have also been utilized to address the limitations in conventional electrical stimulation. Although none of these approaches have been clinically proven to fully restore the function of a degenerated retina, the extensive efforts made in this field have demonstrated a series of encouraging findings for the next generation of retinal prostheses, and these could potentially enhance the visual acuity of retinal prostheses. In this article, a comprehensive and up-to-date overview of retinal prosthetic strategies is provided, with a specific focus on a quantitative assessment of visual acuity results from various retinal stimulation technologies. The aim is to highlight future directions toward high-resolution retinal prostheses.

High-Capacity, Fast-Response, and Photocapacitor-Based Terpolymer Phosphor Composite

This paper describes a new class of light transducer-based poly (vinylidene fluoride-trifluoroethylene-chlorotrifluoroethylene) (P(VDF-TrFE-CTFE)) terpolymer doped with 50% wt. phosphor particles that enables to efficiently transform light energy into an electrical signal. Broadband dielectric characterization together with experimental results on photo-electric conversion demonstrated high capacitance variation of the proposed composite under light exposure, confirming promising potential of our sensor device for application in retinal prostheses where the converted electrical signal can affect the biological activity of the neuron system. In addition to the benefit of being light-weight, having ultra-flexibility, and used in a simple process, the proposed photodetector composite leads to fast response and high sensibility in terms of photoelectrical coupling where significant increases in capacitance change of 78% and 25% have been recorded under blue and green light sources, respectively. These results demonstrated high-performance material design where phosphor filler contributes to promote charge-discharge efficiency as well as reduced dielectric loss in P(VDF-TrFE-CTFE), which facilitate the composite for flexible light transducer applications, especially in the medical environment.

Biomimetic carbon nanotubes for neurological disease therapeutics as inherent medication

Nowadays, nanotechnology is revolutionizing the approaches to different fields from manufacture to health. Carbon nanotubes (CNTs) as promising candidates in nanomedicine have great potentials in developing novel entities for central nervous system pathologies, due to their excellent physicochemical properties and ability to interface with neurons and neuronal circuits. However, most of the studies mainly focused on the drug delivery and bioimaging applications of CNTs, while neglect their application prospects as therapeutic drugs themselves. At present, the relevant reviews are not available yet. Herein we summarized the latest advances on the biomedical and therapeutic applications of CNTs in vitro and in vivo for neurological diseases treatments as inherent therapeutic drugs. The biological mechanisms of CNTs-mediated bio-medical effects and potential toxicity of CNTs were also intensely discussed. It is expected that CNTs will exploit further neurological applications on disease therapy in the near future.

Biocompatible Quantum Funnels for Neural Photostimulation

Neural photostimulation has high potential to understand the working principles of complex neural networks and develop novel therapeutic methods for neurological disorders. A key issue in the light-induced cell stimulation is the efficient conversion of light to bioelectrical stimuli. In photosynthetic systems developed in millions of years by nature, the absorbed energy by the photoabsorbers is transported via nonradiative energy transfer to the reaction centers. Inspired by these systems, neural interfaces based on biocompatible quantum funnels are developed that direct the photogenerated charge carriers toward the bionanojunction for effective photostimulation. Funnels are constructed with indium-based rainbow quantum dots that are assembled in a graded energy profile. Implementation of a quantum funnel enhances the generated photoelectrochemical current 215% per unit absorbance in comparison with ungraded energy profile in a wireless and free-standing mode and facilitates optical neuromodulation of a single cell. This study indicates that the control of charge transport at nanoscale can lead to unconventional and effective neural interfaces.

Nanostructure Endows Neurotherapeutic Potential in Optogenetics: Current Development and Future Prospects

Optogenetics have evolved as a promising tool to control the processes at a cellular level via photons. Specially, it confers a specific control over cellular function through real-time cytomodulation even in freely moving animals. Neuronal stimulation is prerequisite for deep tissue light penetration or insertion of optrode for light illumination to the neurons that have been proven to be compromised due to poor light penetration and invasiveness of the procedure, respectively. In this review, the application of nanotechnology is being elaborated by the use of metal nanoparticles (AuNPs), upconversion nanocrystals (UCNPs), and quantum dots (CdSe) for targeting particular organs or tissues, and their potential to emit a specific light on excitation to overcome the limitations associated with earlier methods has been elucidated. The optothermal and magnetothermal properties, photoluminescence, and higher photostability of nanomaterials are explored in context of therapeutic applicability of optogenetics. The nanostructure characteristics and specific ion channel targeting have shown promising therapeutic potential against neurodegenerative disorders (Alzheimer's, Parkinson's, Huntington's), epilepsy, and blindness. This review compiles mechanical and optical characteristics of nanomaterials that endow superior optogenetic therapeutic potentials to cure immedicable infirmities.

High-Aspect-Ratio Semiconducting Polymer Pillars for 3D Cell Cultures

Hybrid interfaces between living cells and nano/microstructured scaffolds have huge application potential in biotechnology, spanning from regenerative medicine and stem cell therapies to localized drug delivery and from biosensing and tissue engineering to neural computing. However, 3D architectures based on semiconducting polymers, endowed with responsivity to visible light, have never been considered. Here, we apply for the first time a push-coating technique to realize high aspect ratio polymeric pillars, based on polythiophene, showing optimal biocompatibility and allowing for the realization of soft, 3D cell cultures of both primary neurons and cell line models. HEK-293 cells cultured on top of polymer pillars display a remarkable change in the cell morphology and a sizable enhancement of the membrane capacitance due to the cell membrane thinning in correspondence to the pillars' top surface, without negatively affecting cell proliferation. Electrophysiology properties and synapse number of primary neurons are also very well preserved. In perspective, high aspect ratio semiconducting polymer pillars may find interesting applications as soft, photoactive elements for cell activity sensing and modulation.

Nongenetic optical neuromodulation with silicon-based materials

Optically controlled nongenetic neuromodulation represents a promising approach for the fundamental study of neural circuits and the clinical treatment of neurological disorders. Among the existing material candidates that can transduce light energy into biologically relevant cues, silicon (Si) is particularly advantageous due to its highly tunable electrical and optical properties, ease of fabrication into multiple forms, ability to absorb a broad spectrum of light, and biocompatibility. This protocol describes a rational design principle for Si-based structures, general procedures for material synthesis and device fabrication, a universal method for evaluating material photoresponses, detailed illustrations of all instrumentation used, and demonstrations of optically controlled nongenetic modulation of cellular calcium dynamics, neuronal excitability, neurotransmitter release from mouse brain slices, and brain activity in the mouse brain in vivo using the aforementioned Si materials. The entire procedure takes ~4-8 d in the hands of an experienced graduate student, depending on the specific biological targets. We anticipate that our approach can also be adapted in the future to study other systems, such as cardiovascular tissues and microbial communities.

Tuning the Coupling in Single-Molecule Heterostructures: DNA-Programmed and Reconfigurable Carbon Nanotube-Based Nanohybrids

Herein a strategy is presented for the assembly of both static and stimuli-responsive single-molecule heterostructures, where the distance and electronic coupling between an individual functional nanomoiety and a carbon nanostructure are tuned via the use of DNA linkers. As proof of concept, the formation of 1:1 nanohybrids is controlled, where single quantum dots (QDs) are tethered to the ends of individual carbon nanotubes (CNTs) in solution with DNA interconnects of different lengths. Photoluminescence investigations-both in solution and at the single-hybrid level-demonstrate the electronic coupling between the two nanostructures; notably this is observed to progressively scale, with charge transfer becoming the dominant process as the linkers length is reduced. Additionally, stimuli-responsive CNT-QD nanohybrids are assembled, where the distance and hence the electronic coupling between an individual CNT and a single QD are dynamically modulated via the addition and removal of potassium (K+) cations; the system is further found to be sensitive to K+ concentrations from 1 pM to 25 × 10-3 m. The level of control demonstrated here in modulating the electronic coupling of reconfigurable single-molecule heterostructures, comprising an individual functional nanomoiety and a carbon nanoelectrode, is of importance for the development of tunable molecular optoelectronic systems and devices.

Effective Neural Photostimulation Using Indium-Based Type-II Quantum Dots

Light-induced stimulation of neurons via photoactive surfaces offers rich opportunities for the development of therapeutic methods and high-resolution retinal prosthetic devices. Quantum dots serve as an attractive building block for such surfaces, as they can be easily functionalized to match the biocompatibility and charge transport requirements of cell stimulation. Although indium-based colloidal quantum dots with type-I band alignment have attracted significant attention as a nontoxic alternative to cadmium-based ones, little attention has been paid to their photovoltaic potential as type-II heterostructures. Herein, we demonstrate type-II indium phosphide/zinc oxide core/shell quantum dots that are incorporated into a photoelectrode structure for neural photostimulation. This induces a hyperpolarizing bioelectrical current that triggers the firing of a single neural cell at 4 μW mm^-2, 26-fold lower than the ocular safety limit for continuous exposure to visible light. These findings show that nanomaterials can induce a biocompatible and effective biological junction and can introduce a route in the use of quantum dots in photoelectrode architectures for artificial retinal prostheses.

The evolution of artificial light actuators in living systems: from planar to nanostructured interfaces

Artificially enhancing light sensitivity in living cells allows control of neuronal paths or vital functions avoiding the wiring associated with the use of stimulation electrodes. Many possible strategies can be adopted for reaching this goal, including the direct photoexcitation of biological matter, the genetic modification of cells or the use of opto-bio interfaces. In this review we describe different light actuators based on both inorganic and organic semiconductors, from planar abiotic/biotic interfaces to nanoparticles, that allow transduction of a light signal into a signal which in turn affects the biological activity of the hosting system. In particular, we will focus on the application of thiophene-based materials which, thanks to their unique chemical-physical properties, geometrical adaptability, great biocompatibility and stability, have allowed the development of a new generation of fully organic light actuators for in vivo applications.

Direct Electrical Neurostimulation with Organic Pigment Photocapacitors

An efficient nanoscale semiconducting optoelectronic system is reported, which is optimized for neuronal stimulation: the organic electrolytic photocapacitor. The devices comprise a thin (80 nm) trilayer of metal and p-n semiconducting organic nanocrystals. When illuminated in physiological solution, these metal-semiconductor devices charge up, transducing light pulses into localized displacement currents that are strong enough to electrically stimulate neurons with safe light intensities. The devices are freestanding, requiring no wiring or external bias, and are stable in physiological conditions. The semiconductor layers are made using ubiquitous and nontoxic commercial pigments via simple and scalable deposition techniques. It is described how, in physiological media, photovoltage and charging behavior depend on device geometry. To test cell viability and capability of neural stimulation, photostimulation of primary neurons cultured for three weeks on photocapacitor films is shown. Finally, the efficacy of the device is demonstrated by achieving direct optoelectronic stimulation of light-insensitive retinas, proving the potential of this device platform for retinal implant technologies and for stimulation of electrogenic tissues in general. These results substantiate the conclusion that these devices are the first non-Si optoelectronic platform capable of sufficiently large photovoltages and displacement currents to enable true capacitive stimulation of excitable cells.

Nongenetic Optical Methods for Measuring and Modulating Neuronal Response

The ability to probe and modulate electrical signals sensitively at cellular length scales is a key challenge in the field of electrophysiology. Electrical signals play integral roles in regulating cellular behavior and in controlling biological function. From cardiac arrhythmias to neurodegenerative disorders, maladaptive phenotypes in electrophysiology can result in serious and potentially deadly medical conditions. Understanding how to monitor and to control these behaviors precisely and noninvasively represents an important step in developing next-generation therapeutic devices. As we develop a deeper understanding of neural network formation, electrophysiology has the potential to offer fundamental insights into the inner working of the brain. In this Perspective, we explore traditional methods for examining neural function, discuss recent genetic advances in electrophysiology, and then focus on the latest innovations in optical sensing and stimulation of action potentials in neurons. We emphasize nongenetic optical methods, as these provide high spatiotemporal resolution and can be achieved with minimal invasiveness.

Thermo-plasmonic gold nanofilms for simple and mass-producible photothermal neural interfaces

In recent years, photothermal stimulation methods using plasmonic metal nanoparticles have emerged as non-genetic optical techniques in neuromodulation. Although nanoparticle-based photothermal stimulation shows great potential in the excitation and the inhibition of neural activity, the complex synthesis processes of the nanoparticles and the lack of large-area deposition methods can be limiting factors for the development of photothermal neural devices. In this paper, we propose a plasmonic gold nanofilm, fabricated by a standard thermal evaporation process, as a simple and mass-producible photothermal neural interface layer for microelectrode array (MEA) chips. The absorption of the gold nanofilm at near infrared wavelengths is optimized to maximize the photothermal effect by varying the thickness and microstructure of the gold nanofilm. With the optimized conditions, a significantly strong photothermal effect is applied on MEAs without affecting the neural signal recording capability. Finally, primary rat hippocampal neuronal cultures are used to show that the photothermal neural inhibition using the gold nanofilm is as effective as that using the plasmonic nanoparticles. Due to the greater simplicity and versatility of the fabrication process, the plasmonic gold nanofilm can provide a promising solution for the mass production of photothermal platforms.

Design and validation of a foldable and photovoltaic wide-field epiretinal prosthesis

Retinal prostheses have been developed to fight blindness in people affected by outer retinal layer dystrophies. To date, few hundred patients have received a retinal implant. Inspired by intraocular lenses, we have designed a foldable and photovoltaic wide-field epiretinal prosthesis (named POLYRETINA) capable of stimulating wireless retinal ganglion cells. Here we show that within a visual angle of 46.3 degrees, POLYRETINA embeds 2215 stimulating pixels, of which 967 are in the central area of 5 mm, it is foldable to allow implantation through a small scleral incision, and it has a hemispherical shape to match the curvature of the eye. We demonstrate that it is not cytotoxic and respects optical and thermal safety standards; accelerated ageing shows a lifetime of at least 2 years. POLYRETINA represents significant progress towards the improvement of both visual acuity and visual field with the same device, a current challenging issue in the field.

Nanowire arrays restore vision in blind mice

The restoration of light response with complex spatiotemporal features in retinal degenerative diseases towards retinal prosthesis has proven to be a considerable challenge over the past decades. Herein, inspired by the structure and function of photoreceptors in retinas, we develop artificial photoreceptors based on gold nanoparticle-decorated titania nanowire arrays, for restoration of visual responses in the blind mice with degenerated photoreceptors. Green, blue and near UV light responses in the retinal ganglion cells (RGCs) are restored with a spatial resolution better than 100 µm. ON responses in RGCs are blocked by glutamatergic antagonists, suggesting functional preservation of the remaining retinal circuits. Moreover, neurons in the primary visual cortex respond to light after subretinal implant of nanowire arrays. Improvement in pupillary light reflex suggests the behavioral recovery of light sensitivity. Our study will shed light on the development of a new generation of optoelectronic toolkits for subretinal prosthetic devices.

The restoration of light response using retinal prosthesis could be a way to restore vision following retinal degenerative disease. Here the authors develop gold-titania nanowire arrays that restore visual response in blind mice.

Carbon Nanomaterials in Biological Studies and Biomedicine

The "carbon nano-world" has made over the past few decades huge contributions in diverse scientific disciplines and technological advances. While dramatic advances have been widely publicized in using carbon nanomaterials such as fullerenes, carbon nanotubes, and graphene in materials sciences, nano-electronics, and photonics, their contributions to biology and biomedicine have been noteworthy as well. This Review focuses on the use of carbon nanotubes (CNTs), graphene, and carbon quantum dots [encompassing graphene quantum dots (GQDs) and carbon dots (C-dots)] in biologically oriented materials and applications. Examples of these remarkable nanomaterials in bio-sensing, cell- and tissue-imaging, regenerative medicine, and other applications are presented and discussed, emphasizing the significance of their unique properties and their future potential.

Cellular interfaces with hydrogen-bonded organic semiconductor hierarchical nanocrystals

Successful formation of electronic interfaces between living cells and semiconductors hinges on being able to obtain an extremely close and high surface-area contact, which preserves both cell viability and semiconductor performance. To accomplish this, we introduce organic semiconductor assemblies consisting of a hierarchical arrangement of nanocrystals. These are synthesised via a colloidal chemical route that transforms the nontoxic commercial pigment quinacridone into various biomimetic three-dimensional arrangements of nanocrystals. Through a tuning of parameters such as precursor concentration, ligands and additives, we obtain complex size and shape control at room temperature. We elaborate hedgehog-shaped crystals comprising nanoscale needles or daggers that form intimate interfaces with the cell membrane, minimising the cleft with single cells without apparent detriment to viability. Excitation of such interfaces with light leads to effective cellular photostimulation. We find reversible light-induced conductance changes in ion-selective or temperature-gated channels.Nanomaterials that form a bioelectronic interface with cells are fascinating tools for controlling cellular behavior. Here, the authors photostimulate single cells with spiky assemblies of semiconducting quinacridone nanocrystals, whose nanoscale needles maximize electronic contact with the cells.

Meclofenamic acid improves the signal to noise ratio for visual responses produced by ectopic expression of human rod opsin

PURPOSE

Retinal dystrophy through outer photoreceptor cell death affects 1 in 2,500 people worldwide with severe impairment of vision in advanced stages of the disease. Optogenetic strategies to restore visual function to animal models of retinal degeneration by introducing photopigments to neurons spared degeneration in the inner retina have been explored, with variable degrees of success. It has recently been shown that the non-steroidal anti-inflammatory and non-selective gap-junction blocker meclofenamic acid (MFA) can enhance the visual responses produced by an optogenetic actuator (channelrhodopsin) expressed in retinal ganglion cells (RGCs) in the degenerate retina. Here, we set out to determine whether MFA could also enhance photoreception by another optogenetic strategy in which ectopic human rod opsin is expressed in ON bipolar cells.

METHODS

We used in vitro multielectrode array (MEA) recordings to characterize the light responses of RGCs in the rd¹ mouse model of advanced retinal degeneration following intravitreal injection of an adenoassociated virus (AAV2) driving the expression of human rod opsin under a minimal grm6 promoter active in ON bipolar cells.

RESULTS

We found treated retinas were light responsive over five decades of irradiance (from 10¹¹ to 10¹⁵ photons/cm²/s) with individual RGCs covering up to four decades. Application of MFA reduced the spontaneous firing rate of the visually responsive neurons under light- and dark-adapted conditions. The change in the firing rate produced by the 2 s light pulses was increased across all intensities following MFA treatment, and there was a concomitant increase in the signal to noise ratio for the visual response. Restored light responses were abolished by agents inhibiting glutamatergic or gamma-aminobutyric acid (GABA)ergic signaling in the MFA-treated preparation.

CONCLUSIONS

These results confirm the potential of MFA to inhibit spontaneous activity and enhance the signal to noise ratio of visual responses in optogenetic therapies to restore sight.

Carbon Nanotube and Semiconductor Nanorods Hybrids: Preparation, Characterization, and Evaluation of Photocurrent Generation

Carbon nanotubes (CNTs) and semiconductor nanocrystals (SCNCs) are known to be interesting donor-acceptor partners due to their unique optical and electronic properties. These exciting features have led to the development of novel composites based on these two nanomaterials and to their characterization for use in various applications, such as components in sensors, transistors, solar cells and biomedical devices. Two approaches based on covalent and noncovalent methods have been suggested for coupling the SCNCs to CNTs. Most covalent conjugation methods used so far were found to disrupt the electronic structure of the CNTs or interfere with charge transfer in the CNT-SCNC interface. Moreover, it offers random and poorly organized nanoparticle coatings. Therefore, noncovalent methods are considered to be ideal for better electronic coupling. However, a key common drawback of noncovalent methods is the lack of stability which hampers their applicability. In this article, a method has been developed to couple semiconductor seeded nanorods onto CNTs through π-π interactions. The CNTs and pyrene conjugated SCNC hybrid materials were characterized by both microscopic and spectroscopic techniques. Fluorescence and photocurrent measurements suggest the proposed pi-stacking approach results in a strong electronic coupling between the CNTs and the SCNCs leading to better photocurrent efficiency than that of a covalent conjugation method reported using similar SCNC material. Overall, the CNT-SCNC films reported in the present study open the scope for the fabrication of optoelectronic devices for various applications.

Next-generation probes, particles, and proteins for neural interfacing

Bidirectional interfacing with the nervous system enables neuroscience research, diagnosis, and therapy. This two-way communication allows us to monitor the state of the brain and its composite networks and cells as well as to influence them to treat disease or repair/restore sensory or motor function. To provide the most stable and effective interface, the tools of the trade must bridge the soft, ion-rich, and evolving nature of neural tissue with the largely rigid, static realm of microelectronics and medical instruments that allow for readout, analysis, and/or control. In this Review, we describe how the understanding of neural signaling and material-tissue interactions has fueled the expansion of the available tool set. New probe architectures and materials, nanoparticles, dyes, and designer genetically encoded proteins push the limits of recording and stimulation lifetime, localization, and specificity, blurring the boundary between living tissue and engineered tools. Understanding these approaches, their modality, and the role of cross-disciplinary development will support new neurotherapies and prostheses and provide neuroscientists and neurologists with unprecedented access to the brain.