Multifunctional Nanomaterials for Advancing Neural Interfaces: Recording, Stimulation, and Beyond.

ConspectusNeurotechnology has seen dramatic improvements in the last three decades. The major focus in the field has been to design electrical communication platforms with high spatial resolution, stability, and translatability for understanding and affecting neural pathways. The deployment of nanomaterials in bioelectronics has enhanced the capabilities of conventional approaches employing microelectrode arrays (MEAs) for electrical interfaces, allowing the construction of miniaturized, high-performance neuroelectronics (Garg, R.; et al. ACS Appl. Nano Mater. 2023, 6, 8495). While these advancements in the electrical neuronal interface have revolutionized neurotechnology both in scale and breadth, an in-depth understanding of neurons' interactions is challenging due to the complexity of the environments where the cells and tissues are laid. The activity of large, three-dimensional neuronal systems has proven difficult to accurately monitor and modulate, and chemical cell-cell communication is often completely neglected. Recent breakthroughs in nanotechnology have provided opportunities to use new nonelectric modes of communication with neurons and to significantly enhance electrical signal interface capabilities. The enhanced electrochemical activity and optical activity of nanomaterials owing to their nonbulk electronic properties and surface nanostructuring have seen extensive utilization. Nanomaterials' enhanced optical activity enables remote neural state modulation, whereas the defect-rich surfaces provide an enormous number of available electrocatalytic sites for neurochemical detection and electrochemical modulation of cell microenvironments through Faradaic processes. Such unique properties can allow multimodal neural interrogation toward generating closed-loop interfaces with access to more complete neural state descriptors. In this Account, we will review recent advances and our efforts spearheaded toward utilizing nanostructured electrodes for enhanced bidirectional interfaces with neurons, the application of unique hybrid nanomaterials for remote nongenetic optical stimulation of neurons, tunable nanomaterials for highly sensitive and selective neurotransmitter detection, and the utilization of nanomaterials as electrocatalysts toward electrochemically modulating cellular activity. We highlight applications of these technologies across cell types through nanomaterial engineering with a focus on multifunctional graphene nanostructures applied though several modes of neural modulation but also an exploration of broad material classes for maximizing the potency of closed-loop bioelectronics.

Electrocatalytic on-site oxygenation for transplanted cell-based-therapies.

Implantable cell therapies and tissue transplants require sufficient oxygen supply to function and are limited by a delay or lack of vascularization from the transplant host. Previous exogenous oxygenation strategies have been bulky and had limited oxygen production or regulation. Here, we show an electrocatalytic approach that enables bioelectronic control of oxygen generation in complex cellular environments to sustain engineered cell viability and therapy under hypoxic stress and at high cell densities. We find that nanostructured sputtered iridium oxide serves as an ideal catalyst for oxygen evolution reaction at neutral pH. We demonstrate that this approach exhibits a lower oxygenation onset and selective oxygen production without evolution of toxic byproducts. We show that this electrocatalytic on site oxygenator can sustain high cell loadings (>60k cells/mm3) in hypoxic conditions in vitro and in vivo. Our results showcase that exogenous oxygen production devices can be readily integrated into bioelectronic platforms, enabling high cell loadings in smaller devices with broad applicability.

Tailored Electronic Structure of Ir in High Entropy Alloy for Highly Active and Durable Bifunctional Electrocatalyst for Water Splitting under an Acidic Environment.

Proton-exchange-membrane water electrolysis (PEMWE) requires an efficient and durable bifunctional electrocatalyst for the hydrogen evolution reaction (HER) and oxygen evolution reaction (OER). Herein, Ir-based electrocatalyst is designed using the high entropy alloy (HEA) platform of ZnNiCoIrX with two elements (X: Fe and Mn). A facile dealloying in the vacuum system enables the construction of a nanoporous structure with high crystallinity using Zn as a sacrificial element. Especially, Mn incorporation into HEAs tailors the electronic structure of the Ir site, resulting in the d-band center being far away from the Fermi level. Downshifting of the d-band center weakens the adsorption energy with reaction intermediates, which is beneficial for catalytic reactions. Despite low Ir content, ZnNiCoIrMn delivers only 50 mV overpotential for HER at -50 mA cm-2 and 237 mV overpotential for the OER at 10 mA cm-2 . Furthermore, ZnNiCoIrMn shows almost constant voltage for the HER and OER for 100 h and a high stability number of 3.4 × 105 nhydrogen nIr -1 and 2.4 × 105 noxygen nIr -1 , demonstrating the exceptional durability of the HEA platform. The compositional engineering of ZnNiCoIrMn limits the diffusion of elements by high entropy effects and simultaneously tailors the electronic structure of active Ir sites, resulting in the modified cohesive and adsorption energies, all of which can suppress the dissolution of elements.

Epitaxial Growth of Nanostructured Li2 Se on Lithium Metal for All Solid-State Batteries.

Lithium is considered to be the ultimate anode material for high energy-density rechargeable batteries. Recent emerging technologies of all solid-state batteries based on sulfide-based electrolytes raise hope for the practical use of lithium, as it is likely to suppress lithium dendrite growth. However, such devices suffer from undesirable side reactions and a degradation of electrochemical performance. In this work, nanostructured Li2 Se epitaxially grown on Li metal by chemical vapor deposition are investigated as a protective layer. By adjusting reaction time and cooling rate, a morphology of as-prepared Li2 Se is controlled, resulting in nanoparticles, nanorods, or nanowalls with a dominant (220) plane parallel to the (110) plane of the Li metal substrate. Uniaxial pressing the layers under a pressure of 50 MPa for a cell preparation transforms more compact and denser. Dual compatibility of the Li2 Se layers with strong chemical bonds to Li metal and uniform physical contact to a Li6 PS5 Csulfide electrolyte prevents undesirable side reactions and enables a homogeneous charge transfer at the interface upon cycling. As a result, a full cell coupled with a LiCoO2 -based cathode shows significantly enhanced electrochemical performance and demonstrates the practical use of Li anodes with Li2 Se layers for all solid-state battery applications.