Two-Dimensional Nanomaterial-based Metasurfaces for enhanced Plasmonic Sensing – 2DPS

The project was based on the complementarity of two partners (IEMN in France and CINTRA in Singapore) concerning the technological processes for the realization of SPR sensors as well as the related modeling and characterization techniques.
We first developed new SPR optical configurations based on angular, Goos-Hänchen (GH) shift and magnetoplasmonic interrogation schemes. They have been used to characterize the performance of two kinds of sensors:
- conventionnal plasmonic sensors (using a gold surface) on which have been transferred 2D materials (graphene, MoS2 and WS2) that have been obtained by plasma deposition processes at CINTRA in various combinations.
- magneto-optic SPR sensors including different compositions of magneto-optical layers that have been deposited by PVD at IEMN.
The functionalization of the two families of sensors using “click” chemistry has been carried out at IEMN in order to be able capturing and detecting molecules of interest.

- Dual coating of sensor surface by graphene and WS2 layers can improve the sensitivity by one order of magnitude versus conventional SPR sensors.
- Concerning MO-SPR sensors, nano-structured magnetic materials allow for a reduction in the magnetic field required for operation, a more linear behavior, and the magnetoelastic properties of the layer offer new methods for the modulation of the plasmonic signal.
- It is possible to functionalize the surfaces using “click” chemistry allowing the grafting of aptamers that can be designed for the detection of a large number of molecules.

Taking into account the pandemic situation which limited the experimental developments and did not allow the planned displacements between the two partners, the balance of the project is nevertheless satisfactory. The study of different combinations of 2D materials has shown that the WS2 + graphene combination improves the sensitivity. Similarly, the results on MO-SPR sensors have given rise to new perspectives. In the last part of the project, SPR devices with 2D materials dedicated to the detection of SARS-CoV2 have been studied at CINTRA. The WS2 surface functionalization solution developed at IEMN is a priori compatible with the use of aptamers compatible with the target proteins in the virus detection.

The ANR/NRF project has resulted in 7 publications in international peer-reviewed journals and 3 communications in international conferences.

Graphene is known as the thinnest two-dimensional (2D) material in the world. Its high charge carrier mobility is of high interest for surface plasmon resonance (SPR) sensors that are one of the most commonly used optical sensors for real-time monitoring molecular interactions. By coating graphene layers on the metallic SPR sensing substrate, strong electric field enhancement at the metal/graphene interface is induced due to effective charge transfer, but the absorption rate of a graphene monolayer is only 2.3% which impedes the light transfer to plasmon resonance. In this project, we will study the transition metal dichalcogenide (TMDC) nanomaterials as complementary parts to graphene for their higher absorption rates and lower electron energy losses. In a “beyond the state of the art” part will also be investigated the combination of 2D materials to magneto-optically enhanced SPR sensors (MO-SPR). The goal is to reach the required high sensitivity for detecting trace-amount molecules during diagnostic processes, while being able to miniaturize the devices into compact, low-cost transportable ones. Here, we propose to detect TNF-a antigen, which is an endogenous tumor promoter for the early-stage development of cancer (molecular weight of 17 kDa).
Previously, we have designed a graphene-gold SPR sensing structure providing the detection limit of 1 aM (10-18M) for 7.3kDa 24-mer ssDNA which is much lower than those reported for current state-of-the-art graphene-based SPR biosensor, Au NP-enhanced phase-sensitive SPR techniques, gold nanorod-enhanced localized SPR sensors and even nanomechanical biosensors. In these “metasurfaces”, the drastic concentration of plasmon electric field in the 2D plane provides a novel sensing functionality. However, the absorption rate of monolayer graphene is only 2.3%, which makes it difficult to achieve a higher sensitivity that is required for target samples with low molecular weight less than 400 Da in complex matrices such as saliva, urine, serum and marine water. Based on our experience, the main objectives to be pursued under the proposed project are outlined below: (i) To develop a novel plasmonic sensor based on optimized 2D nanostructures for achieving ultra-high sensitivity for the hard-to-identify small molecules mentioned above; (ii) To explore new physics on the plasmonic and magneto-plasmonic effects generated by the coupling between the 2D nanomaterials and gold metasurfaces such as Au/ferromagnetic material/Au stacks, gold nano-arrays, gold nano-grooves (iii) To miniaturize the sensors into portable devices for in-situ detection and to increase their commercialisation potential.
This research project will be performed in a close collaboration between UMI CINTRA at Singapore - a joint laboratory between CNRS, Nanyang Technological University (NTU) and Thales and Institut d’Electronique, de Microélectronique et de Nanotechnologie (IEMN) in Lille, France. The Project matched well with the nanophotonic thrust topic in both research centres. In this project, the Singaporean group members include Prof. Ken-Tye Yong, Dr. Shuwen Zeng and Prof. Philippe Coquet, from CINTRA and Prof. Ho Sup Yoon from School of Biological Sciences of NTU, while the French groups members include Dr. Nicolas Tiercelin, Dr. Rabah Boukherroub and Dr. Jean-Pierre Vilcot from IEMN. The Singaporean groups will be responsible to develop state-of-art plasmonic setups for measuring the intensity and phase signals from the reflected light passing from the sample solutions and fabricate the 2D nanomaterial metasurface-based sensing film, while the French groups will be responsible for the characterization of the nanomaterials, development of MO-SPR devices and surface functionalization of the nano-sensing film to increase the specificity of the sensing devices. Target biomarker samples in complex matrices such as saliva, urine and serum will be collected from National University Hospital close to NTU.