Plasma treatment unlocks ultra-sensitive, metal-free, reusable sensors based on graphene-MoS₂
image: The vertical stacking of graphene and MoS₂ forms a van der Waals heterostructure, leveraging synergistic interlayer coupling to increase electron density and facilitate efficient charge transfer at the interface. The plasma treatment modifies the graphene surface by introducing structural defects and oxygen-containing groups, significantly improving charge transfer and light absorption efficiency. This combined approach achieves molecular detection limits comparable to traditional metal-based SERS sensors while offering advantages such as lower cost, better reproducibility, and substrate reusability. This advancement opens new possibilities for sensitive environmental monitoring and biomedical diagnostics.
Credit: NANO RESEARCH, Tsinghua University Press
Surface-enhanced Raman scattering (SERS) is a powerful, non-destructive technique for detecting molecules at extremely low concentrations, crucial for applications such as biomedical diagnostics, environmental contamination detection, and food safety monitoring. However, traditional metal-based SERS sensors face challenges like high costs and poor reproducibility. Seeking alternatives, scientists have turned to 2D materials like graphene, valued for their flat surface, electronic properties, and flexibility. However, their limited light absorption and molecular interaction reduce SERS sensitivity compared to metal nanostructures.
Addressing these issues, a team led by Dr. Haiyan Zhao at Tsinghua University has developed a metal-free SERS platform by layering graphene onto molybdenum disulfide (MoS2), creating a van der Waals heterostructure. Crucially, they introduced an oxygen plasma treatment step to modify the heterostructure's surface and electronic properties.
Their research demonstrates that the plasma treatment significantly enhances the interaction between light and the heterostructure material. "We found that introducing oxygen plasma treatment creates defects and oxygen-containing functional groups on the surface," explains Jiayun pei, first author of the study. "This modification not only improves the material's ability to absorb light but also facilitates a more efficient charge transfer process between the substrate and the target molecules being detected. Both factors contribute to a stronger Raman signal, enabling much higher sensitivity."
The research demonstrated that this plasma-treated graphene-MoS2 substrate could detect Rhodamine 6G (a common dye molecule used for testing SERS performance) at concentrations as low as 10-9 Molar which rivals part traditional metal-based SERS substrates. Notably, this metal-free platform offers distinct advantages, including significantly lower production costs, improved signal uniformity, and exceptional reusability.
"A significant advantage of our approach is that it's entirely metal-free," Jiayun Pei notes. "This avoids the cost and uniformity issues associated with noble metals. Furthermore, our graphene-MoS2 substrate proved to be remarkably reusable. We demonstrated that it could be cleaned and reused multiple times without a significant drop in performance, which makes it highly attractive for practical applications, especially where sustainability and cost-effectiveness are essential."
Looking ahead, the team aims to expand this technology for broader sensing applications, including biomedical diagnostics and environmental monitoring. "Our ultimate goal is to translate this platform into practical, portable sensing devices for real-world applications, potentially impacting areas like water quality monitoring and food safety analysis." Jiayun Pei stated.
The team published their findings in Nano Research on April 20, 2025.
Other contributors include Fan Yang from Tsinghua University. This work was supported by the National Natural Science Foundations of China (51975320), the Beijing Natural Science Foundation (M22011), and the State Key Laboratory of Clean and Efficient Turbomachinery Power Equipment.
About the Authors
Jiayun Pei received his Bachelor's degree from the Hefei University of Technology. Now he is a PhD candidate at Tsinghua University. His research interest focuses on the processing and property modification of 2D materials.
About Nano Research
Nano Research is a peer-reviewed, open access, international and interdisciplinary research journal, sponsored by Tsinghua University and the Chinese Chemical Society, published by Tsinghua University Press on the platform SciOpen. It publishes original high-quality research and significant review articles on all aspects of nanoscience and nanotechnology, ranging from basic aspects of the science of nanoscale materials to practical applications of such materials. After 18 years of development, it has become one of the most influential academic journals in the nano field. Nano Research has published more than 1,000 papers every year from 2022, with its cumulative count surpassing 7,000 articles. In 2024 InCites Journal Citation Reports, its 2024 IF is 9.0 (8.7, 5 years), and it continues to be the Q1 area among the four subject classifications. Nano Research Award, established by Nano Research together with TUP and Springer Nature in 2013, and Nano Research Young Innovators (NR45) Awards, established by Nano Research in 2018, have become international academic awards with global influence.