Inverted Ion Current Rectification-Based Chemical Delivery Probes for Stimulation of Neurons

On-Site Formation of Functional Dopaminergic Presynaptic Terminals on Neuroligin-2-Modified Gold-Coated Microspheres

Advancements in neural interface technologies have enabled the direct connection of neurons and electronics, facilitating chemical communication between neural systems and external devices. One promising approach is a synaptogenesis-involving method, which offers an opportunity for synaptic signaling between these systems. Janus synapses, one type of synaptic interface utilizing synaptic cell adhesion molecules for interface construction, possess unique features that enable the determination of location, direction of signal flow, and types of neurotransmitters involved, promoting directional and multifaceted communication. This study presents the first successful establishment of a Janus synapse between dopaminergic (DA) neurons and abiotic substrates by using a neuroligin-2 (NLG2)-mediated synapse-inducing method. NLG2 immobilized on gold-coated microspheres can induce synaptogenesis upon contact with spatially isolated DA axons. The induced DA Janus synapses exhibit stable synaptic activities comparable to that of native synapses over time, suggesting their suitability for application in neural interfaces. By calling for DA presynaptic organizations, the NLG2-immobilized abiotic substrate is a promising tool for the on-site detection of synaptic dopamine release.

Streamlining the interface between electronics and neural systems for bidirectional electrochemical communication

Seamless neural interfaces conjoining neurons and electrochemical devices hold great potential for highly efficient signal transmission across neural systems and the external world. Signal transmission through chemical sensing and stimulation via electrochemistry is remarkable because communication occurs through the same chemical language of neurons. Emerging strategies based on synaptic interfaces, iontronics-based neuromodulation, and improvements in selective neurosensing techniques have been explored to achieve seamless integration and efficient neuro-electronics communication. Synaptic interfaces can directly exchange signals to and from neurons, in a similar manner to that of chemical synapses. Hydrogel-based iontronic chemical delivery devices are operationally compatible with neural systems for improved neuromodulation. In this perspective, we explore developments to improve the interface between neurons and electrodes by targeting neurons or sub-neuronal regions including synapses. Furthermore, recent progress in electrochemical neurosensing and iontronics-based chemical delivery is examined.

Poly(ethylene glycol) diacrylate based hydrogel filled micropore with enhanced sensing capability

Ionic current rectification (ICR) phenomena conventionally occurs in nanopores which dimensions are comparable to the thickness of their electrical double layers. However, the microscale ICR in a micropore can also exist under some conditions. Here, the charged hydrogel filled conical micropore was constructed to realize microscale ICR. To better understand the micropore ICR, the influences of space charge density of the hydrogel, micropore geometry, the hydrogel filling length as well as the electrolyte concentration and pH were investigated. Furthermore, we developed a PEGDA-based hydrogel filled micropore sensing platform which sensing performance was enhanced due to the weakly charged PEGDA. The promyelocytic leukemia (PML)/retinoic acid receptor alpha (RARA) fusion genes and adenosine triphosphate (ATP) were respectively used as model analytes and the measured detection limits of 0.1 pM were achieved. The successful realization of microscale ICR in a homogenous and functional hydrogel filled micropore suggests that the fabrication, characterization and operation of ICR based devices can be more robust and facilitated for the wider applications.

Learning from the Brain: Bioinspired Nanofluidics

The human brain completes intelligent behaviors such as the generation, transmission, and storage of neural signals by regulating the ionic conductivity of ion channels in neuron cells, which provides new inspiration for the development of ion-based brain-like intelligence. Against the backdrop of the gradual maturity of neuroscience, computer science, and micronano materials science, bioinspired nanofluidic iontronics, as an emerging interdisciplinary subject that focuses on the regulation of ionic conductivity of nanofluidic systems to realize brain-like functionalities, has attracted the attention of many researchers. This Perspective provides brief background information and the state-of-the-art progress of nanofluidic intelligent systems. Two main categories are included: nanofluidic transistors and nanofluidic memristors. The prospects of nanofluidic iontronics' interdisciplinary progress in future artificial intelligence fields such as neuromorphic computing or brain-computer interfaces are discussed. This Perspective aims to give readers a clear understanding of the concepts and prospects of this emerging interdisciplinary field.

Nanoionics from Biological to Artificial Systems: An Alternative Beyond Nanoelectronics

Ion transport under nanoconfined spaces is a ubiquitous phenomenon in nature and plays an important role in the energy conversion and signal transduction processes of both biological and artificial systems. Unlike the free diffusion in continuum media, anomalous behaviors of ions are often observed in nanostructured systems, which is governed by the complex interplay between various interfacial interactions. Conventionally, nanoionics mainly refers to the study of ion transport in solid-state nanosystems. In this review, to extent this concept is proposed and a new framework to understand the phenomena, mechanism, methodology, and application associated with ion transport at the nanoscale is put forward. Specifically, here nanoionics is summarized into three categories, i.e., biological, artificial, and hybrid, and discussed the characteristics of each system. Compared with nanoelectronics, nanoionics is an emerging research field with many theoretical and practical challenges. With this forward-looking perspective, it is hoped that nanoionics can attract increasing attention and find wide range of applications as nanoelectronics.

Accurate delivery of chemicals to a small target using a pressure-driven valved micropipette

We describe a new method for accurately and reproducibly delivering a minute amount of a chemical to a small target in an aqueous environment. Our method is based on a micropipette with a check valve at its tip that can be opened and closed on demand. We demonstrate that this device can produce a flux of 10^-12 l in a short pulse lasting less than 100 ms. The finite width of the pulse is due to molecular dispersion of the chemical, in this case, fluorescein. The chemical distribution near the micropipette tip is measured and compared with the results of a numerical integration assuming stokeslet flow. Our technique is of general utility and has applications in microbiology and neuroscience when a precise control of the spatiotemporal chemical distribution around a specimen is desired.