A recent study published in Small explores a new method to improve the stability of graphene membranes in transmembrane nanofluidic devices. Researchers applied a pyrene-based coating to strengthen adhesion between graphene and its substrate, enhancing device performance and longevity.
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Background
Graphene’s exceptional properties—high electrical conductivity, mechanical strength, and permeability—make it a promising material for membrane technology, with applications in single-molecule sensing, ion filtration, and energy harvesting. However, its practical use in liquid environments is hindered by a tendency to delaminate. As a single layer of carbon atoms in a two-dimensional lattice, graphene is particularly well-suited for selective ion transport in biosensing and energy conversion, yet it often detaches from its substrate when exposed to electrolytic solutions, leading to device failure.
To address this challenge, researchers explored using a pyrene-based adhesion layer. Pyrene compounds are known for their strong π-π interactions, which can reinforce adhesion between graphene and its supporting silicon nitride (SiN) substrate. This study evaluates whether a pyrene coating can effectively prevent delamination and extend the operational lifespan of graphene-based nanofluidic devices.
The Current Study
Researchers developed pyrene-functionalized SiN substrates for graphene membranes. The process began with a silicon chip featuring a 500 μm thick silicon base and a 500 nm SiO2 layer. A 15 μm by 15 μm window was etched into this layer, exposing a 30 nm thick SiN membrane with a 1 μm aperture.
Chemical functionalization was performed to covalently bond a pyrene derivative to the SiN substrate. Using silane and peptide chemistry, they created a robust adhesion layer to promote π-π interactions with graphene during and after transfer. Monocrystalline graphene, produced through chemical vapor deposition (CVD), was then transferred onto the pyrene-functionalized SiN substrate.
To test device performance, researchers immersed the samples in a 0.1 M hydrochloric acid (HCl) solution and measured ion transport. They analyzed transmembrane current and conductance, comparing devices with and without the pyrene layer. Additional evaluations included optical and scanning electron microscopy (SEM) imaging to inspect graphene coverage and stability.
Results and Discussion
The pyrene layer significantly improved graphene transmembrane device performance. The success rate of functional devices increased from just 4 % to 76.2 % after applying the pyrene coating. These devices maintained stable conductance values below 100 mS cm-2 in acidic solutions, demonstrating reduced delamination and ion leakage.
The area-normalized proton conductance of pyrene-functionalized devices averaged 61 ± 46 mS cm-2, aligning with values reported in previous graphene studies. In contrast, devices without the pyrene layer exhibited rapid delamination, with conductance dropping to the bare SiN substrate within hours of exposure to the electrolyte.
Researchers noted that conductance variations could stem from wrinkles and nanoripples in suspended graphene, which may influence ion transport dynamics. The reduced leakage current, combined with improved adhesion from the pyrene layer, allowed for more consistent data collection from a larger sample of graphene devices, reinforcing the approach’s viability for real-world applications.
Conclusion
This study presents a practical solution for stabilizing graphene-based nanofluidic devices, addressing the longstanding issue of delamination in aqueous environments. The use of a covalently bonded pyrene-based adhesion layer not only strengthens the interface between graphene and its substrate but also enhances device stability and reliability.
These findings suggest that pyrene functionalization could lead to more robust graphene-based membranes for applications in ion transport, sensing, and energy conversion. Future research could explore this technique in other two-dimensional materials, expanding the possibilities for nanoscale fluidic technologies.
Journal Reference
Kang X., et al. (2025). Substrate-tight graphene transmembrane-nanofluidic devices. Small 2407140. DOI: 10.1002/smll.202407140, https://onlinelibrary.wiley.com/doi/full/10.1002/smll.202407140