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.

Improved understanding of molecular principles of neuronal communication allows new insights into neurodegenerative diseases and possibly to new therapeutic targets. However, there is a lack of tools able to monitor simultaneously electrical and chemicals signals of single cells. Therefore, we propose the development of a novel graphene-enhanced sensor allowing simultaneous monitoring of these two signals with single cell resolution both in cell cultures and organotypic tissue slices. The sensor will be based on surface plasmon resonance imaging (SPRi) and its ability to provide excellent spatial resolution also to electrochemical measurements. More importantly, by integrating graphene both the sensitivity of SPR detection and the current densities of the electrochemical measurement will be enhanced with concomitantly improved biocompatibility. In addition to generating new knowledge about the interplay of electrical and chemical signals of living cells, the development of the anticipated sensors will be an important step towards novel prostheses based on the bidirectional communication with living cells. The core of the sensor will be a ?cell chip? carrying disk microelectrodes, to which cells adhere, surrounded by cell-free ring microelectrodes. Once cells have adhered to the disk microelectrodes, the ring microelectrodes (modified with enzymes or unmodified) are polarized to a potential that allows oxidation or reduction of signaling molecules secreted by the cells. Subsequently, high-resolution SPR images of the ?cell chip? are recorded at high frame rates (~10000 fps) while a physical or chemical stimulus is applied to the cells. SPR images of cell-covered disk microelectrodes are modulated by changes in the extracellular field potential of the cells (which enables us to monitor e.g. the propagation of action potentials). SPR images of the ring microelectrodes will be altered by changes in local current densities invoked by variations in the local concentrations of signaling molecules and will be used to observe chemical signals from the cells. Neuronal cells change their extracellular field potential within the low millivolts range and release only tiny amounts of signaling molecules. Therefore, the sensitivity of SPRi has to be improved in order to be able to record electrical and chemical signals from cells simultaneously. Graphene has already been proved to enhance the sensitivity of both SPR and electrochemical detection. Hence, graphene and its derivatives will be applied for signal amplification. Our optoelectrochemical approach to measure extracellular field potentials with sub-micrometer resolution will excel voltage sensitive dyes and electrically interrogated microelectrode arrays. In addition, it will provide unprecedented spatial resolution and interference elimination to the electrochemical monitoring of chemical signals from cells.

Potential applications of electromagnetic absorbers strongly increased over the past few years. Radar absorbing materials were mainly used for stealth applications in the past but are now also integrated in industrial processes (electromagnetic compatibility in RF systems, antennas…). Moreover, the strong development of wireless technologies has led to an increase in the human exposure to electromagnetic waves. This fact gives rise to new public health issues and house protection against electromagnetic radiations is thus a pretty hot topic. Potential applications of radar absorbers are nowadays numerous and new technologies have thus to be developed to answer to these growing needs. This project has two main objectives: i) ultra-thin absorbers for low frequency applications (<4 GHz) and ii) 3D absorbers or Frequency Selective Surfaces (FSS). The need in ultra-thin low-frequency absorbers concerns both military and civil engineering. Indeed, at these frequencies, the most efficient solutions consist in using ferrite ceramics (heavy and expensive) or loaded polymer foams (thick). Flexible magnetic composites can also be used but their absorption capacities are lower. This project proposes to design and fabricate ultra-thin absorbers thanks to the coupling of metasurfaces and composite materials. Considering the frequency band of interest (1-4 GHz), potential applications will concern not only stealthiness of military systems but also the house protection against radiations (GSM, Wifi, 3G, 4G) and a decrease of the electromagnetic interactions between civil radars and wind plants. The second objective of the project is to develop technological means for the realization of 3D absorbers and FSS. These 3D objects will be applied to electronic war (protection against electromagnetic attacks) or to electromagnetic compatibility issues (absorbent packaging for microwave devices). 3D printing of composite materials and 3D selective metallization processes will be used to realize the demonstrators.