Single-Cell Photothermal Neuromodulation for Functional Mapping of Neural Networks

Cellular level cryo-neuromodulation using rapid and localized cooling device combined with microelectrode array

Cryotherapy, a rapid and effective medical treatment utilizing low temperatures, has not been widely adopted in clinical practice due to a limited understanding of its mechanisms and efficacy. This challenge stems from the absence of methods for fast, precise, and localized spatiotemporal temperature control, as well as the lack of reliable real-time quantitative techniques for measuring and analyzing the effects of cooling. To address these limitations, this study introduces a cryo-neuromodulation platform that integrates a high-speed precision cooling device with a microelectrode array (MEA) system. This platform enables the investigation of cellular-level cryo-modulation of neuronal activity and its effects on surrounding cells, providing a novel framework for advancing research in cryotherapy and neuromodulation. Experiments show that neurons recovered fully within 1 min of cooling with a fast-cooling rate (-20 °C/s at cooling) and that silenced neurons can influence distant cells via a well-organized network. Extended cooling durations (e.g., 10 min) resulted in altered neuronal dynamics, including delayed recovery and reduced burst activity, highlighting the importance of precise control over cooling parameters. This device offers reversible neural control, with potential applications in both research and clinical settings, such as anesthesia, pain management and treatment of neurological disorders like neocortical seizures.

Nitrogen-Doped Ultrananocrystalline Diamond - Optoelectronic Biointerface for Wireless Neuronal Stimulation

This study presents a semiconducting optoelectronic system for light-controlled non-genetic neuronal stimulation using visible light. The system architecture is entirely wireless, comprising a thin film of nitrogen-doped ultrananocrystalline diamond directly grown on a semiconducting silicon substrate. When immersed in a physiological medium and subjected to pulsed illumination in the visible (595 nm) or near-infrared wavelength (808 nm) range, charge accumulation at the device-medium interface induces a transient ionic displacement current capable of electrically stimulating neurons with high temporal resolution. With a measured photoresponsivity of 7.5 mA W-1, the efficacy of this biointerface is demonstrated through optoelectronic stimulation of degenerate rat retinas using 595 nm irradiation, pulse durations of 50-500 ms, and irradiance levels of 1.1-4.3 mW mm-2, all below the safe ocular threshold. This work presents the pioneering utilization of a diamond-based optoelectronic platform, capable of generating sufficiently large photocurrents for neuronal stimulation in the retina.

Advanced Thermoactive Nanomaterials for Thermomedical Tissue Regeneration: Opportunities and Challenges

Nanomaterials usually possess remarkable properties, including excellent biocompatibility, unique physical and chemical characteristics, and bionic attributes, which make them highly promising for applications in tissue regeneration. Thermal therapy has emerged as a versatile approach for wound healing, nerve repair, bone regeneration, tumor therapy, and antibacterial tissue regeneration. By combining nanomaterials with thermal therapy, multifunctional nanomaterials with thermogenic effects and tissue regeneration capabilities can be engineered to achieve enhanced therapeutic outcomes. This study provides a comprehensive review of the effects of thermal stimulation on cellular and tissue regeneration. Furthermore, it highlights the applications of photothermal, magnetothermal, and electrothermal nanomaterials, and thermally responsive drug delivery systems in tissue engineering. In Addition, the bioactivities and biocompatibilities of several representative thermal nanomaterials are discussed. Finally, the challenges facing thermal nanomaterials are outlined, and future prospects in the field are presented with the aim of offering new opportunities and avenues for the utilization of thermal nanomaterials in tissue regeneration.

Highly Branched Au Superparticles as Efficient Photothermal Transducers for Optical Neuromodulation

Precise neuromodulation is critical for interrogating cellular communication and treating neurological diseases. Nanoscale transducers have emerged as effective interfaces to exert photothermal effects and modulate neural activities with a high spatiotemporal resolution. Ideal materials for this application should possess strong light absorption, high photothermal conversion efficiency, and great biocompatibility for clinical translation. Here, we show that the structurally designed 3D Au superparticles with a highly branched morphology can be promising candidates for nongenetic and remote neuromodulation. The structure-induced blackbody-like absorption endows Au superparticles with photothermal conversion efficiency over 90%, much higher than that of conventional Au nanorods. With the biocompatible polydopamine ligands, Au superparticles can be readily interfaced with primary mouse hippocampal neurons and other cells and can photostimulate or inhibit their activities in both cell networks or with a single-cell resolution. These findings highlight the importance of structural designs as powerful tools to promote the performance of plasmonic materials in neuromodulation and related research of neuroscience and neuroengineering.

A silicon diode-based optoelectronic interface for bidirectional neural modulation

The development of advanced neural modulation techniques is crucial to neuroscience research and neuroengineering applications. Recently, optical-based, nongenetic modulation approaches have been actively investigated to remotely interrogate the nervous system with high precision. Here, we show that a thin-film, silicon (Si)-based diode device is capable to bidirectionally regulate in vitro and in vivo neural activities upon adjusted illumination. When exposed to high-power and short-pulsed light, the Si diode generates photothermal effects, evoking neuron depolarization and enhancing intracellular calcium dynamics. Conversely, low-power and long-pulsed light on the Si diode hyperpolarizes neurons and reduces calcium activities. Furthermore, the Si diode film mounted on the brain of living mice can activate or suppress cortical activities under varied irradiation conditions. The presented material and device strategies reveal an innovated optoelectronic interface for precise neural modulations.

A biodegradable and flexible neural interface for transdermal optoelectronic modulation and regeneration of peripheral nerves

Optoelectronic neural interfaces can leverage the photovoltaic effect to convert light into electrical current, inducing charge redistribution and enabling nerve stimulation. This method offers a non-genetic and remote approach for neuromodulation. Developing biodegradable and efficient optoelectronic neural interfaces is important for achieving transdermal stimulation while minimizing infection risks associated with device retrieval, thereby maximizing therapeutic outcomes. We propose a biodegradable, flexible, and miniaturized silicon-based neural interface capable of transdermal optoelectronic stimulation for neural modulation and nerve regeneration. Enhancing the device interface with thin-film molybdenum significantly improves the efficacy of neural stimulation. Our study demonstrates successful activation of the sciatic nerve in rodents and the facial nerve in rabbits. Moreover, transdermal optoelectronic stimulation accelerates the functional recovery of injured facial nerves.

Augmenting insect olfaction performance through nano-neuromodulation

Biological olfactory systems are highly sensitive and selective, often outperforming engineered chemical sensors in highly complex and dynamic environments. As a result, there is much interest in using biological systems to build sensors. However, approaches to read-out information from biological systems, especially neural signals, tend to be suboptimal due to the number of electrodes that can be used and where these can be placed. Here we aim to overcome this suboptimality in neural information read-out by using a nano-enabled neuromodulation strategy to augment insect olfaction-based chemical sensors. By harnessing the photothermal properties of nanostructures and releasing a select neuromodulator on demand, we show that the odour-evoked response from the interrogated regions of the insect olfactory system can not only be enhanced but can also improve odour identification.

Janus microparticles-based targeted and spatially-controlled piezoelectric neural stimulation via low-intensity focused ultrasound

Electrical stimulation is a fundamental tool in studying neural circuits, treating neurological diseases, and advancing regenerative medicine. Injectable, free-standing piezoelectric particle systems have emerged as non-genetic and wireless alternatives for electrode-based tethered stimulation systems. However, achieving cell-specific and high-frequency piezoelectric neural stimulation remains challenging due to high-intensity thresholds, non-specific diffusion, and internalization of particles. Here, we develop cell-sized 20 μm-diameter silica-based piezoelectric magnetic Janus microparticles (PEMPs), enabling clinically-relevant high-frequency neural stimulation of primary neurons under low-intensity focused ultrasound. Owing to its functionally anisotropic design, half of the PEMP acts as a piezoelectric electrode via conjugated barium titanate nanoparticles to induce electrical stimulation, while the nickel-gold nanofilm-coated magnetic half provides spatial and orientational control on neural stimulation via external uniform rotating magnetic fields. Furthermore, surface functionalization with targeting antibodies enables cell-specific binding/targeting and stimulation of dopaminergic neurons. Taking advantage of such functionalities, the PEMP design offers unique features towards wireless neural stimulation for minimally invasive treatment of neurological diseases.

Intravital photoacoustic brain stimulation with high-precision

Significance

Neural regulation at high precision vitally contributes to propelling fundamental understanding in the field of neuroscience and providing innovative clinical treatment options. Recently, photoacoustic brain stimulation has emerged as a cutting-edge method for precise neuromodulation and shows great potential for clinical application.

Aim

The goal of this perspective is to outline the advancements in photoacoustic brain stimulation in recent years. And, we also provide an outlook delineating several prospective paths through which this burgeoning approach may be substantively refined for augmented capability and wider implementations.

Approach

First, the mechanisms of photoacoustic generation as well as the potential mechanisms of photoacoustic brain stimulation are provided and discussed. Then, the state-of-the-art achievements corresponding to this technology are reviewed. Finally, future directions for photoacoustic technology in neuromodulation are provided.

Results

Intensive research endeavors have prompted substantial advancements in photoacoustic brain stimulation, illuminating the unique advantages of this modality for noninvasive and high-precision neuromodulation via a nongenetic way. It is envisaged that further technology optimization and randomized prospective clinical trials will enable a wide acceptance of photoacoustic brain stimulation in clinical practice.

Conclusions

The innovative practice of photoacoustic technology serves as a multifaceted neuromodulation approach, possessing noninvasive, high-accuracy, and nongenetic characteristics. It has a great potential that could considerably enhance not only the fundamental underpinnings of neuroscience research but also its practical implementations in a clinical setting.

Selective Infrared Neural Inhibition Can Be Reproduced by Resistive Heating

OBJECTIVES

Small-diameter afferent axons carry various sensory signals that are critical for vital physiological conditions but sometimes contribute to pathologies. Infrared (IR) neural inhibition (INI) can induce selective heat block of small-diameter axons, which holds potential for translational applications such as pain management. Previous research suggested that IR-heating-induced acceleration of voltage-gated potassium channel kinetics is the mechanism for INI. Therefore, we hypothesized that other heating methods, such as resistive heating (RH) in a cuff, could reproduce the selective inhibition observed in INI.

MATERIALS AND METHODS

We conducted ex vivo nerve-heating experiments on pleural-abdominal connective nerves of Aplysia californica using both IR and RH. We fabricated a transparent silicone nerve cuff for simultaneous IR heating, RH, and temperature measurements. Temperature elevations (ΔT) on the nerve surface were recorded for both heating modalities, which were tested over a range of power levels that cover a similar ΔT range. We recorded electrically evoked compound action potentials (CAPs) and segmented them into fast and slow subcomponents on the basis of conduction velocity differences between the large and small-diameter axonal subpopulations. We calculated the normalized inhibition strength and inhibition selectivity index on the basis of the rectified area under the curve of each subpopulation.

RESULTS

INI and RH showed a similar selective inhibition effect on CAP subcomponents for slow-conducting axons, confirmed by the inhibition probability vs ΔT dose-response curve based on approximately 2000 CAP measurements. The inhibition selectivity indexes of the two heating modalities were similar across six nerves. RH only required half the total electrical power required by INI to achieve a similar ΔT.

SIGNIFICANCE

We show that selective INI can be reproduced by other heating modalities such as RH. RH, because of its high energy efficiency and simple design, can be a good candidate for future implantable neural interface designs.

Time-Resolved Mid-Infrared Photothermal Microscopy for Imaging Water-Embedded Axon Bundles

Few experimental tools exist for performing label-free imaging of biological samples in a water-rich environment due to the high infrared absorption of water, overlapping with major protein and lipid bands. A novel imaging modality based on time-resolved mid-infrared photothermal microscopy is introduced and applied to imaging axon bundles in a saline bath environment. Photothermally induced spatial gradients at the axon bundle membrane interfaces with saline and surrounding biological tissue are observed and temporally characterized by a high-speed boxcar detection system. Localized time profiles with an enhanced signal-to-noise, hyper-temporal image stacks, and two-dimensional mapping of the time decay profiles are acquired without the need for complex post image processing. Axon bundles are found to have a larger distribution of time decay profiles compared to the water background, allowing background differentiation based on these transient dynamics. The quantitative analysis of the signal evolution over time allows characterizing the level of thermal confinement at different regions. When axon bundles are surrounded by complex heterogeneous tissue, which contains smaller features, a stronger thermal confinement is observed compared to a water environment, thus shedding light on the heat transfer dynamics across aqueous biological interfaces.

Neuronal maturation-dependent nano-neuro interaction and modulation

Nanotechnology-enabled neuromodulation is a promising minimally-invasive tool in neuroscience and engineering for both fundamental studies and clinical applications. However, the nano-neuro interaction at different stages of maturation of a neural network and its implications for the nano-neuromodulation remain unclear. Here, we report heterogeneous to homogeneous transformation of neuromodulation in a progressively maturing neural network. Utilizing plasmonic-fluors as ultrabright fluorescent nanolabels, we reveal that negative surface charge of nanoparticles renders selective nano-neuro interaction with a strong correlation between the maturation stage of the individual neurons in the neural network and the density of the nanoparticles bound on the neurons. In stark contrast to homogeneous neuromodulation in a mature neural network reported so far, the maturation-dependent density of the nanoparticles bound to neurons in a developing neural network resulted in a heterogeneous optical neuromodulation (i.e., simultaneous excitation and inhibition of neural network activity). This study advances our understanding of nano-neuro interactions and nano-neuromodulation with potential applications in minimally-invasive technologies for treating neuronal disorders in parts of the mammalian brain where neurogenesis persists throughout aging.

Emerging trends in the development of flexible optrode arrays for electrophysiology

Optical-electrode (optrode) arrays use light to modulate excitable biological tissues and/or transduce bioelectrical signals into the optical domain. Light offers several advantages over electrical wiring, including the ability to encode multiple data channels within a single beam. This approach is at the forefront of innovation aimed at increasing spatial resolution and channel count in multichannel electrophysiology systems. This review presents an overview of devices and material systems that utilize light for electrophysiology recording and stimulation. The work focuses on the current and emerging methods and their applications, and provides a detailed discussion of the design and fabrication of flexible arrayed devices. Optrode arrays feature components non-existent in conventional multi-electrode arrays, such as waveguides, optical circuitry, light-emitting diodes, and optoelectronic and light-sensitive functional materials, packaged in planar, penetrating, or endoscopic forms. Often these are combined with dielectric and conductive structures and, less frequently, with multi-functional sensors. While creating flexible optrode arrays is feasible and necessary to minimize tissue-device mechanical mismatch, key factors must be considered for regulatory approval and clinical use. These include the biocompatibility of optical and photonic components. Additionally, material selection should match the operating wavelength of the specific electrophysiology application, minimizing light scattering and optical losses under physiologically induced stresses and strains. Flexible and soft variants of traditionally rigid photonic circuitry for passive optical multiplexing should be developed to advance the field. We evaluate fabrication techniques against these requirements. We foresee a future whereby established telecommunications techniques are engineered into flexible optrode arrays to enable unprecedented large-scale high-resolution electrophysiology systems.

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.

Second Near-Infrared (NIR-II) Window for Imaging-Navigated Modulation of Brain Structure and Function

For a long time, optical imaging of the deep brain with high resolution has been a challenge. Recently, with the advance in second near-infrared (NIR-II) bioimaging techniques and imaging contrast agents, NIR-II window bioimaging has attracted great attention to monitoring deeper biological or pathophysiological processes with high signal-to-noise ratio (SNR) and spatiotemporal resolution. Assisted with NIR-II bioimaging, the modulation of structure and function of brain is promising to be noninvasive and more precise. Herein, in this review, first the advantage of NIR-II light in brain imaging from the interaction between NIR-II and tissue is elaborated. Then, several specific NIR-II bioimaging technologies are introduced, including NIR-II fluorescence imaging, multiphoton fluorescence imaging, and photoacoustic imaging. Furthermore, the corresponding contrast agents are summarized. Next, the application of various NIR-II bioimaging technologies in visualizing the characteristics of cerebrovascular network and monitoring the changes of the pathology signals will be presented. After that, the modulation of brain structure and function based on NIR-II bioimaging will be discussed, including treatment of glioblastoma, guidance of cell transplantation, and neuromodulation. In the end, future perspectives that would help improve the clinical translation of NIR-II light are proposed.

High temporal resolution transparent thermoelectric temperature sensors for photothermal effect sensing

We propose inkjet-printed high-speed and transparent temperature sensors based on the thermoelectric effect for direct monitoring of the photothermal effect. They consist of highly transparent organic thermoelectric materials that allow excellent biocompatibility and sub-ms temporal resolution, simultaneously. Our transparent thermoelectric temperature sensors can be used to advance various photothermal biomedical applications.

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.

Bioresorbable thin-film silicon diodes for the optoelectronic excitation and inhibition of neural activities

Neural activities can be modulated by leveraging light-responsive nanomaterials as interfaces for exerting photothermal, photoelectrochemical or photocapacitive effects on neurons or neural tissues. Here we show that bioresorbable thin-film monocrystalline silicon pn diodes can be used to optoelectronically excite or inhibit neural activities by establishing polarity-dependent positive or negative photovoltages at the semiconductor/solution interface. Under laser illumination, the silicon-diode optoelectronic interfaces allowed for the deterministic depolarization or hyperpolarization of cultured neurons as well as the upregulated or downregulated intracellular calcium dynamics. The optoelectronic interfaces can also be mounted on nerve tissue to activate or silence neural activities in peripheral and central nervous tissues, as we show in mice with exposed sciatic nerves and somatosensory cortices. Bioresorbable silicon-based optoelectronic thin films that selectively excite or inhibit neural tissue may find advantageous biomedical applicability.

Enhancement of Thermoplasmonic Neural Modulation Using a Gold Nanorod-Immobilized Polydopamine Film

Photothermal neural activity inhibition has emerged as a minimally invasive neuromodulation technology with submillimeter precision. One of the techniques involves the utilization of plasmonic gold nanoparticles (AuNPs) to modulate neural activity by photothermal effects ("thermoplasmonics"). A surface modification technique is often required to integrate AuNPs onto the neural interface. Here, polydopamine (pDA), a multifunctional adhesive polymer with a wide light absorption spectrum, is introduced both as a primer layer for the immobilization of gold nanorods (GNRs) on the neural interface and as an additional photothermal agent by absorbing near-infrared red (NIR) lights for more efficient photothermal effects. First, the optical and photothermal properties of pDA as well as the characteristics of GNRs attached onto the pDA film are investigated for the optimized photothermal neural interface. Due to the covalent bonding between GNR surfaces and pDA, GNRs immobilized on pDA showed strong attachment onto the surface, yielding a more stable photothermal platform. Lastly, when photothermal neural stimulation was applied to the primary rat hippocampal neurons, the substrate with GNRs immobilized on the pDA film allowed more laser power-efficient photothermal neuromodulation as well as photothermal cell death. This study suggests the feasibility of using pDA as a surface modification material for developing a photothermal platform for the inhibition of neural activities.

Injectable Black Phosphorus Nanosheets for Wireless Nongenetic Neural Stimulation

Neurons can be modified to express light-sensitive proteins for enabling stimulation with a high spatial and temporal resolution, but such techniques require gene transfection and systematical implantation. Here, a black phosphorus nanosheet-based injectable strategy is described for wireless neural stimulation both in vitro and in vivo without cell modifications. These nanosheets, with minimal invasiveness, high biocompatibility, and biodegradability, are anchored on cell membranes as miniature near-infrared (NIR) light transducers to create local heating for neural activity excitation. Based on cultured multielectrode-array recording, in vivo electrophysiology analysis, and open field behavioral tests, it is demonstrated that remotely applied NIR illumination can reliably trigger spiking activity in cultured neurons and rat brains. Excitingly, reliable regulation of brain function to control animal behaviors is also described. Moreover, this approach has shown its potential for future clinical use by successful high-frequency stimulation in cells and animals in this proof-of-concept study. It is believed that this new method will offer a powerful alternative to other neural stimulation solutions and potentially be of independent value to the healthcare system.

Single infrared light pulses induce excitatory and inhibitory neuromodulation

The excitatory and inhibitory effects of single and brief infrared (IR) light pulses (2 µm) with millisecond durations and various power levels are investigated with a custom-built fiber amplification system. Intracellular recordings from motor axons of the crayfish opener neuromuscular junction are performed ex vivo. Single IR light pulses induce a membrane depolarization during the light pulses, which is followed by a hyperpolarization that can last up to 100 ms. The depolarization amplitude is dependent on the optical pulse duration, total energy deposition and membrane potential, but is insensitive to tetrodotoxin. The hyperpolarization reverses its polarity near the potassium equilibrium potential and is barium-sensitive. The membrane depolarization activates an action potential (AP) when the axon is near firing threshold, while the hyperpolarization reversibly inhibits rhythmically firing APs. In summary, we demonstrate for the first time that single and brief IR light pulses can evoke initial depolarization followed by hyperpolarization on individual motor axons. The corresponding mechanisms and functional outcomes of the dual effects are investigated.

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.

Closed-loop control of neural spike rate of cultured neurons using a thermoplasmonics-based photothermal neural stimulation

Objective.Photothermal neural stimulation has been developed in a variety of interfaces as an alternative technology that can perturb neural activity. The demonstrations of these techniques have heavily relied on open-loop stimulation or complete suppression of neural activity. To extend the controllability of photothermal neural stimulation, combining it with a closed-loop system is required. In this work, we investigated whether photothermal suppression mechanism can be used in a closed-loop system to reliably modulate neural spike rate to non-zero setpoints.Approach. To incorporate the photothermal inhibition mechanism into the neural feedback system, we combined a thermoplasmonic stimulation platform based on gold nanorods (GNRs) and near-infrared illuminations (808 nm, spot size: 2 mm or 200μm in diameter) with a proportional-integral (PI) controller. The closed-loop feedback control system was implemented to track predetermined target spike rates of hippocampal neuronal networks cultured on GNR-coated microelectrode arrays.Main results. The closed-loop system for neural spike rate control was successfully implemented using a PI controller and the thermoplasmonic neural suppression platform. Compared to the open-loop control, the target-channel spike rates were precisely modulated to remain constant or change in a sinusoidal form in the range below baseline spike rates. The spike rate response behaviors were affected by the choice of the controller gain. We also demonstrated that the functional connectivity of a synchronized bursting network could be altered by controlling the spike rate of one of the participating channels.Significance.The thermoplasmonic feedback controller proved that it can precisely modulate neural spike rate of neural activityin vitro. This technology can be used for studying neuronal network dynamics and might provide insights in developing new neuromodulation techniques in clinical applications.

Laser Power Determination Using Light-to-Heat Conversion Rate of Nanoplasmonic Substrates for Neural Stimulation

Since neurons have temperature sensitive properties, gold nanorod (GNR)-mediated photothermal stimulation has been developed as a neuromodulation application. As an in vitro photothermal platform, GNR-layer was integrated with substrates to effectively apply heat stimulation to the cultured neurons. However, identifying optimal laser power for a targeted temperature on the substrate requires the consideration of thermal properties of the GNR-coated substrates. In this report, we suggest a simple numerical method to determine incident laser power on the substrates for a targeted temperature.

All-Optical and Label-Free Stimulation of Action Potentials in Neurons and Cardiomyocytes by Plasmonic Porous Metamaterials

Optical stimulation technologies are gaining great consideration in cardiology, neuroscience studies, and drug discovery pathways by providing control over cell activity with high spatio-temporal resolution. However, this high precision requires manipulation of biological processes at genetic level concealing its development from broad scale application. Therefore, translating these technologies into tools for medical or pharmacological applications remains a challenge. Here, an all-optical nongenetic method for the modulation of electrogenic cells is introduced. It is demonstrated that plasmonic metamaterials can be used to elicit action potentials by converting near infrared laser pulses into stimulatory currents. The suggested approach allows for the stimulation of cardiomyocytes and neurons directly on commercial complementary metal-oxide semiconductor microelectrode arrays coupled with ultrafast pulsed laser, providing both stimulation and network-level recordings on the same device.

Molecular Nature of Structured Water in the Light-Induced Interfacial Capacitance Changes at the Bioelectric Interface

Uncovering the function of structured water in the interfacial capacitance at the molecular level is the basis for the development of the concept and model of the electric double layer; however, the limitation of the available technology makes this task difficult. Herein, using surface-enhanced infrared absorption spectroscopy combined with electrochemistry, we revealed the contribution of the cleavage of loosely bonded tetrahedral water to the enhancement of model membrane capacitance. Upon further combination with ionic perturbation, we found that the interface hydrogen bonding environment in the stern layer was greatly significant for the light-induced cleavage of tetrahedral water and thus the conversion of optical signals into electrical signals. Our work has taken an important step toward gaining experimental insight into the relationship between water structure and capacitance at the bioelectric interface.

Current Review of Optical Neural Interfaces for Clinical Applications

Neural interfaces, which enable the recording and stimulation of living neurons, have emerged as valuable tools in understanding the brain in health and disease, as well as serving as neural prostheses. While neural interfaces are typically based on electrical transduction, alternative energy modalities have been explored to create safe and effective approaches. Among these approaches, optical methods of linking neurons to the outside world have gained attention because light offers high spatial selectivity and decreased invasiveness. Here, we review the current state-of-art of optical neural interfaces and their clinical applications. Optical neural interfaces can be categorized into optical control and optical readout, each of which can be divided into intrinsic and extrinsic approaches. We discuss the advantages and disadvantages of each of these methods and offer a comparison of relative performance. Future directions, including their clinical opportunities, are discussed with regard to the optical properties of biological tissue.

Reversible Photothermal Modulation of Electrical Activity of Excitable Cells using Polydopamine Nanoparticles

Advances in the design and synthesis of nanomaterials with desired biophysicochemical properties can be harnessed to develop non-invasive neuromodulation technologies. Here, the reversible modulation of the electrical activity of neurons and cardiomyocytes is demonstrated using polydopamine (PDA) nanoparticles as photothermal nanotransducers. In addition to their broad light absorption and excellent photothermal activity, PDA nanoparticles are highly biocompatible and biodegradable, making them excellent candidates for both in vitro and in vivo applications. The modulation of the activity (i.e., spike rate of the neurons and beating rate of cardiomyocytes) of excitable cells can be finely controlled by varying the excitation power density and irradiation duration. Under optimal conditions, reversible suppression (≈100%) of neural activity and reversible enhancement (two-fold) in the beating rate of cardiomyocytes is demonstrated. To improve the ease of interfacing of photothermal transducers with these excitable cells and enable spatial localization of the photothermal stimulus, a collagen/PDA nanoparticle foam is realized, which can be used as an "add-on patch" for photothermal stimulation. The non-genetic optical neuromodulation approach using biocompatible and biodegradable nanoparticles represents a minimally invasive method for controlling the activity of excitable cells with potential applications in nano-neuroscience and engineering.

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.

Bond-selective imaging by optically sensing the mid-infrared photothermal effect

Mid-infrared (IR) spectroscopic imaging using inherent vibrational contrast has been broadly used as a powerful analytical tool for sample identification and characterization. However, the low spatial resolution and large water absorption associated with the long IR wavelengths hinder its applications to study subcellular features in living systems. Recently developed mid-infrared photothermal (MIP) microscopy overcomes these limitations by probing the IR absorption-induced photothermal effect using a visible light. MIP microscopy yields submicrometer spatial resolution with high spectral fidelity and reduced water background. In this review, we categorize different photothermal contrast mechanisms and discuss instrumentations for scanning and widefield MIP microscope configurations. We highlight a broad range of applications from life science to materials. We further provide future perspective and potential venues in MIP microscopy field.

Mirroring Action Potentials: Label-Free, Accurate, and Noninvasive Electrophysiological Recordings of Human-Derived Cardiomyocytes

The electrophysiological recording of action potentials in human cells is a long-sought objective due to its pivotal importance in many disciplines. Among the developed techniques, invasiveness remains a common issue, causing cytotoxicity or altering unpredictably cell physiological response. In this work, a new approach for recording intracellular signals of outstanding quality and with noninvasiveness is introduced. By taking profit of the concept of mirror charge in classical electrodynamics, the new proposed device transduces cell ionic currents into mirror charges in a microfluidic chamber, thus realizing a virtual mirror cell. By monitoring mirror charge dynamics, it is possible to effectively record the action potentials fired by the cells. Since there is no need for accessing or interacting with the cells, the method is intrinsically noninvasive. In addition, being based on optical recording, it shows high spatial resolution and high parallelization. As shown through a set of experiments, the presented methodology is an ideal candidate for the next generation devices for the reliable assessment of cardiotoxicity on human-derived cardiomyocytes. More generally, it paves the way toward a new family of in vitro biodevices that will lay a new milestone in the field of electrophysiology.

Emerging Frontier of Peripheral Nerve and Organ Interfaces

The development of new tools to interface with the nervous system, empowered by advances in electronics and materials science, has transformed neuroscience and is informing therapies for neurological and mental conditions. Although the vast majority of neural engineering research has focused on advancing tools to study the brain, understanding the peripheral nervous system and other organs can similarly benefit from these technologies. To realize this vision, the neural interface technologies need to address the biophysical, mechanical, and chemical challenges posed by the peripheral nerves and organs. In this Perspective, we discuss design considerations and recent technological advances to modulate electrical signaling outside the central nervous system. The innovations in bioelectronics borne out of interdisciplinary collaborations between biologists and physical scientists may not only advance fundamental study of peripheral (neuro)physiology but also empower clinical interventions for conditions including neurological, gastrointestinal, and immune dysfunction.

Thermoplasmonic neural chip platform for in situ manipulation of neuronal connections in vitro

Cultured neuronal networks with a controlled structure have been widely studied as an in vitro model system to investigate the relationship between network structure and function. However, most cell culture techniques lack the ability to control network structures during cell cultivation, making it difficult to assess functional changes induced by specific structural changes. In this study, we present an in situ manipulation platform based on gold-nanorod-mediated thermoplasmonics to interrogate an in vitro network model. We find that it is possible to induce new neurite outgrowths, eliminate interconnecting neurites, and estimate functional relationships in matured neuronal networks. This method is expected to be useful for studying functional dynamics of neural networks under controlled structural changes.

Cultured neuron networks provide insight into network structure and function, but the ability to control network topology is a challenge. Here the authors develop a nanorod-mediated thermoplasmonics platform that enables the formation of new connections, the abolishment of existing connections, and the modulation of network activity during cultivation.

Recent advances in bioelectronics chemistry

Research in bioelectronics is highly interdisciplinary, with many new developments being based on techniques from across the physical and life sciences. Advances in our understanding of the fundamental chemistry underlying the materials used in bioelectronic applications have been a crucial component of many recent discoveries. In this review, we highlight ways in which a chemistry-oriented perspective may facilitate novel and deep insights into both the fundamental scientific understanding and the design of materials, which can in turn tune the functionality and biocompatibility of bioelectronic devices. We provide an in-depth examination of several developments in the field, organized by the chemical properties of the materials. We conclude by surveying how some of the latest major topics of chemical research may be further integrated with bioelectronics.

Thermoplasmonic Optical Fiber for Localized Neural Stimulation

Thermoplasmonic effect-based neural stimulation has been suggested as an alternative optical neural stimulation technology without genetic modification. Integration of near-infrared light with plasmonic gold nanoparticles has been demonstrated as a neuromodulation tool on in vitro neuronal network models. In order to further test the validity of the thermoplasmonic neural stimulation across multiple biological models (in vitro, ex vivo, and in vivo) avoiding genetic modification in optical neuromodulation, versatile engineering approaches to apply the thermoplasmonic effect would be required. In this work, we developed a gold nanorod attached optical fiber technology for the localized neural stimulation based on a thermoplasmonic effect. A simple fabrication process was developed for efficient nanoparticle coating on commercial optical fibers. The thermoplasmonic optical fiber proved that it can locally modulate the neural activity in vitro. Lastly, we simulated the spatiotemporal temperature change by the thermoplasmonic optical fiber and analyzed its applicability to in vivo animal models.

Progress in Brain-Compatible Interfaces with Soft Nanomaterials

Neural interfaces facilitating communication between the brain and machines must be compatible with the soft, curvilinear, and elastic tissues of the brain and yet yield enough power to read and write information across a wide range of brain areas through high-throughput recordings or optogenetics. Biocompatible-material engineering has facilitated the development of brain-compatible neural interfaces to support built-in modulation of neural circuits and neurological disorders. Recent developments in brain-compatible neural interfaces that use soft nanomaterials more suitable for complex neural circuit analysis and modulation are reviewed. Preclinical tests of the compatibility and specificity of these interfaces in animal models are also discussed.

Label-free optical detection of bioelectric potentials using electrochromic thin films

Understanding how a network of interconnected neurons receives, stores, and processes information in the human brain is one of the outstanding scientific challenges of our time. The ability to reliably detect neuroelectric activities is essential to addressing this challenge. Optical recording using voltage-sensitive fluorescent probes has provided unprecedented flexibility for choosing regions of interest in recording neuronal activities. However, when recording at a high frame rate such as 500 to 1,000 Hz, fluorescence-based voltage sensors often suffer from photobleaching and phototoxicity, which limit the recording duration. Here, we report an approach called electrochromic optical recording (ECORE) that achieves label-free optical recording of spontaneous neuroelectrical activities. ECORE utilizes the electrochromism of poly(3,4-ethylenedioxythiophene) polystyrene sulfonate (PEDOT:PSS) thin films, whose optical absorption can be modulated by an applied voltage. Being based on optical reflection instead of fluorescence, ECORE offers the flexibility of an optical probe without suffering from photobleaching or phototoxicity. Using ECORE, we optically recorded spontaneous action potentials in cardiomyocytes, cultured hippocampal and dorsal root ganglion neurons, and brain slices. With minimal perturbation to cells, ECORE allows long-term optical recording over multiple days.

Folate-Modified Photoelectric Responsive Polymer Microarray as Bionic Artificial Retina to Restore Visual Function

A high-optical-resolution artificial retina system that accurately communicates with the optic nerve is the main challenge in the modern biological science and bionic field. Here, we developed a bionic artificial retina possessing phototransduction "cells" with measurements even smaller than that of the neural cells. Using the technique of micrometer processing, we constructed a pyramid-shape periodic microarray of a photoreceptor. Each "sensing cell" took advantage of polythiophene derivative/fullerene derivative (PCBM) as a photoelectric converter. Because folic acid played an essential role in eye growth, we particularly modified the polythiophene derivatives with folic acid tags. Therefore, the artificial retina could enlarge the contact area and even recognize the nerve cells to improve the consequence of nerve stimulation. We implanted the artificial retina into blinded rats' eyes. Electrophysiological analysis revealed its recovery of photosensitive function 3 months after surgery. Our work provides an innovative idea for fabricating a high-resolution bionic artificial retina system. It shows great potential in artificial intelligence and biomedicine.

Near-Infrared Light Triggered-Release in Deep Brain Regions Using Ultra-photosensitive Nanovesicles

Remote and minimally-invasive modulation of biological systems with light has transformed modern biology and neuroscience. However, light absorption and scattering significantly prevents penetration to deep brain regions. Herein, we describe the use of gold-coated mechanoresponsive nanovesicles, which consist of liposomes made from the artificial phospholipid Rad-PC-Rad as a tool for the delivery of bioactive molecules into brain tissue. Near-infrared picosecond laser pulses activated the gold-coating on the surface of nanovesicles, creating nanomechanical stress and leading to near-complete vesicle cargo release in sub-seconds. Compared to natural phospholipid liposomes, the photo-release was possible at 40 times lower laser energy. This high photosensitivity enables photorelease of molecules down to a depth of 4 mm in mouse brain. This promising tool provides a versatile platform to optically release functional molecules to modulate brain circuits.

Intracellular Recording of Human Cardiac Action Potentials on Market-Available Multielectrode Array Platforms

High quality attenuated intracellular action potentials from large cell networks can be recorded on multi-electrode arrays by means of 3D vertical nanopillars using electrical pulses. However, most of the techniques require complex 3D nanostructures that prevent the straightforward translation into marketable products and the wide adoption in the scientific community. Moreover, 3D nanostructures are often delicate objects that cannot sustain several harsh use/cleaning cycles. On the contrary, laser optoacoustic poration allows the recording of action potentials on planar nanoporous electrodes made of noble metals. However, these constraints of the electrode material and morphology may also hinder the full exploitation of this methodology. Here, we show that optoacoustic poration is also very effective for porating cells on a large family of MEA electrode configurations, including robust electrodes made of nanoporous titanium nitride or disordered fractal-like gold nanostructures. This enables the recording of high quality cardiac action potentials in combination with optoacoustic poration, providing thus attenuated intracellular recordings on various already commercial devices used by a significant part of the research and industrial communities.

A synergistic optical strategy for enhanced deep-tumor penetration and therapy in the second near-infrared window

A mesoporous core–shell nanohybrid allows delivery of thermophilic enzymes for stromal depletion and high photothermal conversion efficiency for tumor therapy.

Plasmonic Nanofactors as Switchable Devices to Promote or Inhibit Neuronal Activity and Function

Gold nanosystems have been investigated extensively for a variety of applications, from specific cancer cell targeting to tissue regeneration. Specifically, a recent and exciting focus has been the gold nanosystems' interface with neuronal biology. Researchers are investigating the ability to use these systems neuronal applications ranging from the enhancement of stem cell differentiation and therapy to stimulation or inhibition of neuronal activity. Most of these new areas of research are based on the integration of the plasmonic properties of such nanosystems into complex synthetic extracellular matrices (ECM) that can interact and affect positively the activity of neuronal cells. Therefore, the ability to integrate the plasmonic properties of these nanoparticles into multidimensional and morphological structures to support cellular proliferation and activity is potentially of great interest, particularly to address medical conditions that are currently not fully treatable. This review discusses some of the promising developments and unique capabilities offered by the integration of plasmonic nanosystems into morphologically complex ECM devices, designed to control and study the activity of neuronal cells.