Femptoampere Nanofluidic Hydroxide Ionics: Programming Two-Dimensional Electric Fields Inside Angstrom-Scale Graphene Nanocapillaries to Gate Sub-Nanometer Protonic Logic for On-Chip Water-Recycling Neural Prosthetics

Digital painting of nanofluidic ionics with electric fields in graphene nanocapillaries and moving hydroxide and proton ions. — **Figure 1:** This ultra-realistic digital painting visualizes the concept of femptoampere-scale nanofluidic ionics, where 2D electric fields are actively programmed within angstrom-scale graphene nanocapillaries. The painting intricately depicts hydroxide and proton ions being influenced by these fields to form sub-nanometer protonic logic, integral for emerging neural prosthetic technology. An on-chip water-recycling mechanism is seamlessly integrated, showcasing a futuristic approach to neural interfacing. The semi-transparent cutaway view reveals detailed interactions between ions, electric fields, and technological nanostructures, illuminated by soft neon tones against a subdued lab aesthetic background, emphasizing the blend of biological and technological innovation.

The convergence of nanofluidics, two-dimensional (2D) materials, and bioelectronics is paving the way for revolutionary advancements in neural prosthetics. Angstrom-scale graphene nanocapillaries, with their atomically precise channels, enable unprecedented control over ion transport, particularly for protons and hydroxide ions, at currents as low as femtoamperes. This regime not only promises ultra-low-power operation but also integrates water recycling mechanisms directly on-chip, addressing critical challenges in implantable devices such as biofluid management and energy efficiency. Drawing from recent literature on graphene-based nanofluidics, we synthesize findings on ion sieving, voltage-gated transport, and memristive behaviors to propose a framework for programming 2D electric fields that gate sub-nanometer protonic logic. This speculative integration could enable neural prosthetics that mimic synaptic plasticity while recycling water from interstitial fluids, bridging gaps between conflicting reports on ion mobility in confined spaces and highlighting neglected intersections with neuromorphic computing.

Current nanofluidic devices often struggle with balancing selectivity, throughput, and energy consumption, especially for hydroxide-dominated ionics where pH-dependent transport introduces variability. Emerging subfields like photo-enhanced proton transport and elastocapillary switches suggest pathways to dynamic control, yet their application to bioelectronics remains underexplored. By cross-pollinating ideas from superionic conductors in 2D materials and ion rectification diodes, we hypothesize that programmable electric fields in graphene capillaries could achieve femtoampere-scale logic gates, enabling on-chip computation with minimal power draw. This not only resolves contradictions in transport models—such as ultrafast water flow versus hindered ion diffusion—but also poses provocative questions: Could such systems recycle water via electro-osmotic pumping to sustain long-term neural interfaces without external reservoirs?

Nanofluidic Transport in Angstrom-Scale Graphene Channels

Angstrom-scale graphene nanocapillaries represent a cutting-edge platform for nanofluidics, where confinement effects dramatically alter fluid and ion behaviors. Recent studies reveal that water transport through these channels exhibits anomalous ultrafast rates, governed by synergistic effects of confinement size and interfacial interactions. For instance, machine learning-enhanced molecular dynamics simulations show that at interlayer distances ≤12.5 Å, transport is dominated by parallel flows of interfacial "fast water" layers, while larger spacings introduce perpendicular fluctuations that subtly modulate permeability. This conflicts with earlier models assuming continuum hydrodynamics, highlighting an emerging subfield of 2D non-linear hydrodynamics where dilatational viscosity plays a pivotal role in flow compression and velocity saturation under high pressure.

Voltage-gated mechanisms further enrich this landscape, with transmembrane electric fields enabling reversible precipitation and dissolution of metal phosphates in nanopores, achieving rectification ratios exceeding 40,000. Such systems suppress photo-enhanced proton transport under tunable infrared spectra via Pauli blocking, offering a speculative pathway to program 2D electric fields for selective ion gating. Neglected directions include integrating elastocapillary switches, which encapsulate zeptoliter volumes, potentially for on-chip water recycling. We propose that combining these with heteroatom-doped graphene could unify conflicting results on vapor versus liquid transport, where pores ~2.8–6.6 Å favor molecular flow regimes for vapors, yielding orders-of-magnitude differences in permeance. This synthesis suggests a novel hypothesis: programmable confinement could enable femtoampere hydroxide currents by exploiting quantum friction and edge-state transport, underexplored in biofluidic contexts.

Comparisons across domains reveal patterns: while graphene excels in proton sieving, materials like CdPS3 nanosheets offer versatile superionic conduction for multivalent ions, even at sub-zero temperatures. Bridging these, we speculate that angstrom-scale channels could gate sub-nm protonic logic by modulating slip lengths via cation intercalation, resolving debates on whether interfacial friction or pore connectivity limits transport. Future experiments might probe this through Raman-monitored field dragging, analogous to DNA translocation control, to quantify femtoampere thresholds for hydroxide-dominated flows.

Hydroxide and Proton Ionics: Mechanisms and Control

Hydroxide and proton transport in 2D materials underscore a dynamic interplay of hydration, charge, and confinement, with graphene nanocapillaries enabling precise control at the molecular level. Cutting-edge findings indicate that proton transport can be accelerated by low-intensity illumination but suppressed via gate-controlled Pauli blocking, revealing tunable photo-effects. This contrasts with conflicting reports on ion mobility: while some studies show ultrafast proton hopping in angstrom pores, others highlight steric hindrances for hydroxides, suggesting pH-dependent rectification. Emerging subfields like nanofluidic memristors, programmable through electrolyte composition and voltage frequency, mimic synaptic plasticity with volatile and non-volatile memory, pointing to underexplored bioinspired computing.

3D render illustrating hydroxide and proton ionics within graphene nanocapillaries. — **Figure 3:** This high-resolution 3D render visualizes the dynamic mechanisms of hydroxide and proton ionics within 2D graphene nanocapillaries. Programmable 2D electric fields control the flow of hydroxide (OH-) and proton (H+) ions, with visible hydration shells signifying their charged nature and confinement. The image artistically highlights photo-enhanced transport and memristive behaviors, suggesting synaptic plasticity through synaptic-like structures and controllable electric fields that resemble dynamic barriers. Neon and glowing accents emphasize active electric interactions, set against a futuristic scientific backdrop, enhancing the understanding of ion transport within nanoscale confinements.

Ion sieving membranes, such as alginate-pillared Ti3C2Tx, demonstrate exceptional valent cation selectivity, with fixed nanochannels ~7.4 Å achieving >99% rejection. This bridges to hydroxide ionics, where superionic conductors like CdPS3 nanosheets facilitate high-density cation movement, including protons, across wide temperature ranges. We hypothesize that programming 2D electric fields could gate hydroxide flows by inducing concerted ion movements, resolving contradictions in delocalization thresholds observed in non-Hermitian systems. Neglected intersections include combining these with deep eutectic solvents for lignin dissolution, potentially enabling bio-derived electrolytes for sustainable prosthetics.

Speculatively, femtoampere currents arise from residue imaginary velocities in confined hydroxides, unifying frameworks for error-resilient transport. Provocative questions emerge: Could adaptive exceptional points, tuned via chaos-guided dynamics, enable sub-nm protonic logic? Cross-pollinating with aerogel-based nanofibers, which enhance structural stability, suggests that B/N/F-doped hollow-core designs could amplify hydroxide selectivity, fostering water-recycling mechanisms in neural interfaces.

Gating and Logic in Sub-Nanometer Protonic Devices

Sub-nanometer protonic logic in graphene nanocapillaries leverages gated transport to emulate biological ion channels, with femtoampere currents enabling ultra-low-power computation. Recent advancements in ion rectification diodes, using gel polymer electrolytes like PMMA/PVDF-HFP heterojunctions, achieve ratios of 23.11 through differential ion diffusion/migration, operating from -20°C to 125°C. This integrates with programmable memristors in 2D channels, where four memristor types emerge from varying pH and frequency, simulating synaptic depression. Conflicts arise in scaling: while small pores favor free molecular flow for protons, larger ones introduce fluctuations that hinder logic fidelity, underscoring the need for Pauli-blocked gating to suppress unwanted photo-effects.

Ultra-realistic rendering of a sub-nanometer protonic logic device using graphene nanocapillaries, showcasing a logic gate with gated ion transport, ion rectification, and memristive properties. — **Figure 4:** This ultra-realistic rendering depicts a sub-nanometer protonic logic device leveraging graphene nanocapillaries. The image illustrates a pioneering logic gate that operates through gated ion transport, where the differential migration of protons and hydroxides is visually expressed to showcase ion rectification. The device's memristive properties are highlighted, demonstrating non-volatile states crucial for advanced computational applications. Elements in the visualization suggest integration into on-chip water-recycling circuits, indicative of its potential application in neural prosthetics for enhanced biomedical interfacing. This futuristic schematic uses subtle neon tones to highlight electromagnetic interactions within a high-tech environment, offering a glimpse into the promising future of nanoelectronics in biotechnology.

Emerging subfields like transverse field dragging slow DNA translocation 400-fold, a principle extendable to protons for timed logic gates. We propose that 2D electric fields, programmed via bias-tuned Fermi levels, could gate hydroxide-proton pairs, creating non-volatile states for water-recycling circuits. This speculates on unifying iontronic circuits with memristive behaviors, a concept that could revolutionize how we approach biohybrid integrations. Here, materials such as CdPS3 conductors, known for enabling multivalent logic, including Al3+ gates, could offer new levels of robustness and functionality.

A key hypothesis in this domain revolves around the idea of chaos-induced delocalization for infinite-range correlations, which challenges the traditional understanding of locality in protonic devices. To validate this, future experiments might integrate hydrovoltaic technologies, where MXene-based blue energy harvesting could power the on-chip logic. Such an approach would not only be a step forward in creating self-sustaining systems but would also build a critical bridge to the practical implementation of neural prosthetics.

Integration into On-Chip Water-Recycling Neural Prosthetics

On-chip water-recycling neural prosthetics represent a visionary application of nanofluidic hydroxide ionics, where graphene nanocapillaries gate protonic logic while recycling biofluids. Wireless biosensors for real-time monitoring, enhanced by MXenes' hydrophilicity, enable seamless human-machine interfaces, but integration with protonic devices remains underexplored. Cutting-edge MXene hydrovoltaics harvest blue energy from sweat, suggesting self-powered prosthetics that recycle water via osmotic gradients in angstrom channels.

Conflicting results on biocompatibility—e.g., high ion conductivities versus thermal tolerances—highlight patterns: alginate-stabilized membranes offer acid recovery with 100% Na2SO4 rejection, adaptable for interstitial fluid management. We speculate that programming 2D fields could create sub-nm logic gates that double as water pumps, using electro-osmosis to recycle hydroxide-rich fluids, resolving energy constraints in implants.

Neglected directions include ferroptosis-based nanomaterials for BC therapy, analogously inspiring robust bioelectronics. Provocative hypothesis: Femtoampere protonic logic could enable adaptive neural interfaces that self-regulate pH via gated hydroxides, fostering water-neutral operation. This synthesis poses open problems like quantifying biofluid compatibility and scaling for clinical deployment.

Conclusion

Femptoampere nanofluidic hydroxide ionics in graphene nanocapillaries offer transformative potential for neural prosthetics, enabling programmable 2D electric fields to gate protonic logic and recycle water on-chip. By synthesizing cutting-edge transport mechanisms with bioelectronic integrations, this framework resolves transport conflicts and highlights emerging subfields like iontronic memristors. Implications include ultra-low-power implants for chronic neural disorders, with future directions focusing on hybrid MXene-graphene systems for enhanced biocompatibility. Open problems encompass scaling rectification for multi-ion logic and validating in vivo water recycling, urging interdisciplinary experiments to realize this generative vision.

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